hard starting TPI, crossfire or LT1 vette

Discussion in 'Engine: Repairs and Modifications & generally corv' started by grumpyvette, Mar 16, 2009.

  1. grumpyvette

    grumpyvette Administrator Staff Member

    one of the more frequent complaints I hear about is c-4 corvettes that have difficulty or intermittent start problems.
    or occasionally I hear about intermittent missing, that needs to be isolated and tracked down to be corrected.
    READ THE THREAD THRU TO THE END
    AND BE AWARE THAT THIS THREAD,
    AND ALL OTHER THREADS ON THIS SITE ARE CONSTANTLY UPDATED WITH NEW LINKS AND INFO, AS IT BECOMES AVAILABLE

    it is always helps to post your location,when posting questions, at least the city & state your located in because theres a good chance an experienced hobbyist or mechanic on this site may be reading this, located local to you, who is willing to help either for free or at low cost! or at least post advices and places to get parts locally
    theres a great many links posted below that contain a vast amount of related info

    Id start by, pulling trouble codes and cleaning the battery terminals and cable connections carefully, a great many problems blamed on battery's and fuses are basically high resistance or intermittent connections, then use a multi meter to see what your dealing with.
    (yes even if the engine spins over easily and has ignition spark, cleaning the battery terminals usually helps reliability)
    yes IM fully aware that theres at least a few guys on the site that would rather roll around naked in broken glass, than read thru links and do in-depth research before, just jumping into a project and start randomly spend money on replacement parts :lol: :roll: :....but for those who gentlemen who would rather track down the cause of a problem with a few tests and a shop manual and logically approach the issues , in a step bye step manor theres plenty of posted info

    The secret of effective diagnosis and troubleshooting is to have a logical plan.
    The secret of effective diagnosis and troubleshooting is to have a logical, well-ordered system. Following a logical step-by-step procedure will get you to the root cause of a problem quickly and efficiently. and you can,t go into the process assuming you know the answer before you test, let the facts you find lead you to the answers,you may waste a great deal of time chasing what you assume is a bad injector or a faulty ignition only to find its a clogged fuel filter, low fuel pressure or a loose electrical connection, Repair manuals will have a diagnostic tree that goes in a logical progression. It will ask a question, usually yes or no, and depending on the answer will branch off in two or more directions. The last box in the tree will have the problem and how to correct it. The example shown is a simple one. A more complicated system will have branches going into specific tests and then have 2 or more branches from there depending on test results.
    If your experiencing intermittent electrical issues you will obviously need to get out the shop manual for your year corvette, a multi meter and do some isolate and testing, but be aware that loose or corroded connections , will be hard to isolate, as they seldom present a consistent, solid open or dead short in the wire,theres several electrical connector plugs that connect thru the firewall near the battery location that are subject to corrosion issues and frame grounds that might be suspect, obviously theres sensors that can be defective.
    [​IMG]
    links with lots of sub-links that should be useful, most guys ,faced with isolating an electrical issue, seem to get over whelmed, but if you get out the schematics, use a multi meter and some logic in tracing the circuits, and start pulling fuses and measuring resistance and voltage, take the time to read the manual ,pull trouble codes,and if required get a scan tool or a data logging program for your lap top computer, and using the shop manual, you can generally isolate the cause, but don,t get fixated on the idea that all misses are ignition, electrical related, theres potential mechanical, and fuel delivery issues that could be involved.
    OK too trouble shoot a no start condition,you need to understand the basics, you need compression,in all cylinders, consistent fuel,pressure and volume,ignition spark, correct ignition timing, no vacuum leaks and the exhaust must not be really restrictive.
    Don,t assume its a major problem, pull trouble codes and get out a multi-meter....check that your battery has 13 volts?, verify the starter spins the engine, verify your getting fuel pressure and ignition spark and when you find a problem trace it to its source. if you don,t have fuel pressure you should reasonably check in the fuel supply system, but don,t over look silly stuff like your fuel tanks empty, if your engine won,t spin over obviously check the battery and starter function,do you have an alarm or "VATS" system? if you have good battery voltage will the engine spin? are you getting spark at the plugs? and pull your spark plugs to be sure the engines not locked up hydraulically from a leaking head gasket.
    LOOK FOR LOOSE OR CORRODED ELECTRICAL WIRING CONNECTORS, in THE WIRING HARNESS, and VERIFY YOUR FIRING ORDER, YEAH I KNOW YOUR SURE ITS CORRECT, CHECK IT CAREFULLY AGAIN, YOUR NOID TEST LIGHT AND MULTI- METER CAN SAVE YOU A GREAT DEAL OF PROBLEMS AND SCRATCHING YOUR HEAD IF YOU TEST BASIC ELECTRICAL CONNECTIONS< RESISTANCE AND VOLTAGE, CHECK YOUR SENSORS AND GROUNDS, A SHOP MANUALS MANDATORY, HEAT SENSORS, MAF SENSORS, AND IGNITION MODULES AND OIL PRESSURE SENSORS HAVE A LONG TRACK RECORD OF FAILING OR PARTIALLY AND INTERMITTENTLY NOT FUNCTIONING
    if you have voltage at the ignition coil, and no spark don,t assume its a defective ignition coil , but if you have a spare coil swap it out as a quick test, won,t hurt, and it will help isolate the problem source.
    also be aware that a leaking injector, or fuel pressure regulator can cause the catalytic converter, to melt internally, blocking the exhaust flow or oxygen sensors to fail
    remember what goes in needs to go out UNRESTRICTED, and a clogged catalytic converter can cause the engine to run very poorly or not start at all.
    ANYTIME YOUR DEALING WITH THE ENGINE AND HOW IT RUNS ,
    YOULL BE DEALING WITH DIFFERENT ISSUES,
    COOLANT AND OIL TEMPS,& PRESSURE
    FUEL PRESSURE , INJECTOR FUNCTION
    FUEL DELIVERY, PRESSURE & VOLUME
    RELATED FUEL / AIR RATIO
    EFFECTIVE COMPRESSION & RING SEAL
    VALVE TIMING LIFT & DURATION & VALVE SEAL
    IGNITION SPARK TIMING & STRENGTH, & IGNITION ADVANCE CURVE
    EXHAUST BACK PRESSURE
    SENSOR OUTPUT TO THE CPU
    VOLTAGE & GROUNDS
    ITS YOUR JOB TO TEST AND ISOLATE EACH UNTIL THE CAUSE IS LOCATED
    READ

    THE LINKS AND SUB LINKS,
    THEY CONTAIN A HUGE AMOUNT OF RELATED INFO
    PULL THE TROUBLE CODES
    http://garage.grumpysperformance.com/index.php?threads/c4-c5-corvette-trouble-codes.2697/

    http://members.shaw.ca/corvette86/FuelS ... gnosis.pdf

    http://garage.grumpysperformance.com/index.php?threads/testing-leaky-fuel-injectors.7310/

    http://garage.grumpysperformance.co...ystem-trouble-shooting-flow-chart-info.11536/

    http://garage.grumpysperformance.com/index.php?threads/replacing-a-c-4-fuel-pump.33/

    http://garage.grumpysperformance.com/index.php?threads/chasing-a-crazy-electrical-glitch.986/

    http://garage.grumpysperformance.co...lay-switch-locations-and-info.728/#post-43477
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    CHECK ALL YOUR FUSES and electrical connections WITH A MULTI METER, but don,t assume you know what the problem is, let the facts lead you to the answers
    be aware that not all engine "MISSES" or "ticking sounds " that you might be dealing with or tying to correct, are an electrical or a fuel delivery or pressure issue, your problem might be a mechanical issue like a vacuum leak, from a busted hose,or loose gasket,a burnt valve, loose or worn timing chain,badly adjusted valves, broken or loose harmonic damper, loose flex plate, or torque converter bolt, busted valve spring, burnt or defective rocker, loose or worn valve guide, or a dozen other issues so try to logically isolate it to a cylinder or system, electrical,valve train, fuel delivery, exhaust , ignition ,etc.


    [​IMG]
    WATCH THE VIDEO, READ THE LINKS
    http://www.youtube.com/watch?v=9CPqbaSg ... re=related



    http://www.chevythunder.com/fuel%20inje ... pg%20B.htm

    IF you start with checking for loose electrical connections and vacuum leaks you might find the problem, a propane torch is both safer and easier to use as a method to locate vacuum leaks
    check for vacuum leaks

    [​IMG]
    (DONT LIGHT IT) just SLIGHTLY open the valve so its allowing gas to flow at a low volume,start the engine and let it idle at the lowest speed you can then place the tip of the UNLIT torch at any suspected vacuum leak and listen for the rpms to increase and watch the tachometer, gas flowing into a vacuum leak will increase engine speed.
    Another possible quick test you can do relates to "clear flooded engine mode" if the car cranks but doesn't start and has fuel pressure, you can test by trying disconnecting the TPS sensor connection on the pass side of the throttle body,. This will kick the computer into limp home mode (setting a predetermined voltage) and the car will start after a time if you flooded the plenum in the intake
    look for loose or missing vacuum hoses, cracked or broken power brake connections, emissions system hoses that are loose, vacuum connections to the trans or ignition, loose connectors missing or loose bolts cracked hoses missing accessory connections etc.
    naturally this only locates leaks to the outside, and its possible for the intake to suck air from the lifter gallery, so that also needs to be checked if everything else seems to be ok.

    read this


    buy a CHEVY SHOP MANUAL FOR YOUR YEAR CORVETTE!
    set and verify your ignition timing, pull trouble codes,set your tps and iac,, then check for vacuum leaks on the lines and intake,then get out your multi meter and verify all the sensors, chances are good its a defective heat sensor or defective o2 sensor, a logical step by step approach will lead you to the problem, youll be amazed at what youll learn reading links. use of a shop manual and multi meter can be very helpful
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    http://www.harborfreight.com/5-in-1-dig ... 98674.html

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    FLUKE is the brand of choice but they are expensive, shop around, Ive still got the original fluke multi meter I bought in HIGH SCHOOL and it STILL WORKSIve purchase several from harbor freight , in the last 10 years alone and only one still works
    http://www.fluke-direct.com/shop/itemDe ... urer=FLUKE

    http://www.fluke-direct.com/shop/catego ... TERS&path=

    http://chevythunder.com/

    [​IMG]
    a good quality if temp gun helps more than you might realize at diagnosing problems
    http://www.grainger.com/product/EXTECH- ... _-AllPages
    learn to use the factory shop manual, and a multi meter and LISTEN to the engine closely, tapping and high pitch whines can indicate defective injectors or fuel pressure regulators, fuel pumps,mis- adjusted valve train components, worn distributor parts, check all the fuses and electrical grounds and corrosion on connections thats something thats frequently over looked etc.

    http://www.chevythunder.com/Flow chart index.htm

    http://www.professionalequipment.com/ex ... ermometer/


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    having a good cross check tool like a quality IR temp gun, and a decent multi meter, sure helps find the truth as far as a defective gauge or sensor
    viewtopic.php?f=44&t=464

    http://www.corvettebuyers.com/ecm2.html

    http://www.hotrodlane.cc/NewTPI%20links ... ml#tpitech

    http://www.mainstreamtopics.com/forums/ ... iagnostic/

    viewtopic.php?f=55&t=606

    viewtopic.php?f=70&t=5372&p=18557#p18557

    http://chevythunder.com/

    http://www.centuryperformance.com/tunin ... g-148.html
    IF the dash lights but it won,t turn over,or just clicks,take off the battery cables and clean the connections then reassemble the trouble your describing is extremely common on theres cars if the battery connections are not cleaned occasionally, the bad connection passed enough low amp current to light up the dash but once the load increases its not able to supply the required current flow rates, if the engine spins but won,t start, obviously you'll want to check all your FUSES with the multi meter and verify the engine and ECU ground straps (usually on the back of the drivers side cylinder head)are tight connections
    AND AGAIN! LOOK FOR LOOSE OR CORRODED ELECTRICAL WIRING CONNECTORS, in THE WIRING HARNESS, and VERIFY YOUR FIRING ORDER, YEAH I KNOW YOUR SURE ITS CORRECT, CHECK IT CAREFULLY AGAIN, YOUR NOID TEST LIGHT AND MULTI- METER CAN SAVE YOU A GREAT DEAL OF PROBLEMS AND SCRATCHING YOUR HEAD IF YOU TEST BASIC ELECTRICAL CONNECTIONS< RESISTANCE AND VOLTAGE, CHECK YOUR SENSORS AND GROUNDS, A SHOP MANUALS MANDATORY, HEAT SENSORS AND IGNITION MODULES AND OIL PRESSURE SENSORS HAVE A LONG TRACK RECORD OF FAILING OR PARTIALLY AND INTERMITTENTLY NOT FUNCTIONING
    learn to use the factory shop manual, and a multi meter and LISTEN to the engine closely, tapping and high pitch whines can indicate defective injectors or fuel pressure regulators, fuel pumps,mis- adjusted valve train components, worn distributor parts, check all the fuses and electrical grounds and corrosion on connections thats something thats frequently over looked etc.
    it helps a great deal to know what your working with ,ID suggest starting, by verifying TDC and having the correct timing tape on your damper then,start with 8 degrees btdc and verifying the full advance of 36 degrees total is all in at 3200rpm as a base line, once youve got that, as a standard you can tune and run the car and eventually try tweaks to the basic ignition curve if needed, once you have an ignition base line, move on to the carbs tuning, you also need to keep in mind that what goes in as a fuel /air mix needs to go out as a much expended volume of hot gases and a restrictive exhaust will effectively block most attempts to get more power from an engine, so measure exhaust back pressure. you might be amazed at what a couple hours research into the subject will do to help you build a much more durable engine, and actually reading thru links and sub-links and asking questions helps a great deal

    you might be amazed at the number of times "CARBURETOR PROBLEMS" are cured with getting the IGNITION, TIMING AND ADVANCE CURVE WORKING CORRECTLY, and check out the simply things your 100% sure you did correctly, because I can,t begin to tell you how many times I see guys who have the firing order on the ignition wrong, or guys that install a 4/7 swap cam and still use the standard ignition firing order or guys that never verify TDC and ignition advance curves.
    get an IR temp gun and check for wild variations in exhaust temps, get a compression test done, do a logical check to verify each cylinder fires etc.
    The ignition control module in the distributor is another item that normally fails when hot, that needs to be replaced is you suspect its defective


    get out your shop manual and multi meter

    if you suspect the injectors , you first use a multi meter to verify every injector reads the same ohms (usually near 11-16 ohms, and yes they should all read very closely) then you need a noid kit for a G.M. fuel injection system, these are basically little lights that light as the injector pulse hits them that you plug into the injector harness,after you remove the harness from the injectors, they plug into the harness just like an injector, if you try to start the engine and they blink on and off the pulse is reaching the injectors thus proving that the injectors get the pulse

    ANY TIME YOU SUSPECT FUEL INJECTOR OR FUEL SYSTEM RELATED ISSUES ,A REASONABLE START POINT IS TO USE A GOOD QUALITY FUEL INJECTION CLEANER ADDITIVE IN THE FUEL TANK AND SWAP TO A NEW FUEL FILTER
    http://www.bgprod.com/catalog/gasoline- ... m-cleaner/
    http://www.bgprod.com/catalog/gasoline- ... m-cleaner/

    http://www.harborfreight.com/11-piece-n ... 97959.html

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    http://www.chevythunder.com/Flow chart index.htm

    viewtopic.php?f=32&t=6011&p=18597&hilit=isolate+test+basic#p18597

    viewtopic.php?f=32&t=168

    viewtopic.php?f=50&t=9478&p=34812&hilit=camaro+sensors#p34812

    viewtopic.php?f=32&t=596

    viewtopic.php?f=32&t=9746

    viewtopic.php?f=36&t=63&p=31920&hilit=isolate+test+basic#p31920

    viewtopic.php?f=27&t=3096&p=18612&hilit=scan+software#p18612

    http://www.digitalcorvettes.com/forums/ ... p?t=197337

    viewtopic.php?f=44&t=987&p=2395&hilit=intermitant#p2395

    viewtopic.php?f=32&t=596

    http://www.mainstreamtopics.com/forums/ ... iagnostic/

    http://members.shaw.ca/corvette86/FuelS ... gnosis.pdf
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    keep in mind oil temp sensors and oil pressure sensors are notorious for going defective and reading wrong

    then as always ,always drop back to the basics of compression,
    air flow in and exhaust out of the engine,
    ignition spark, strength and timing,
    and fuel delivery,volume and pressure

    oil pressure and temp
    cooling,temps and fluid levels (fuel,oil,coolant)
    computer controls and sensors
    always drop back to the basics
    have you verified theres no vacuum leaks
    have you verified theres at least 37 psi of fuel pressure?
    have you verified theres constantly ignition spark at the plugs?
    have you verified theres spark at OR NEAR TDC on the power stroke with a timing light, timing tape on the damper and verified the timing marks are correct?
    have you verified theres 12 volts at the coil?
    have you verified the coil fires?
    have you verified there spark at the plugs?
    have you verified the injectors get voltage with a noid light?
    have you verified the fuel injection fuses are good?
    have you verified all the sensors are good?
    all electrical connections are correct?
    have you pulled trouble codes?
    have you verified the firing order?
    have you readjusted the valves so you know 100% that they are not too tight?
    are you getting about 10psi of oil pressure or more as the engine turns over?
    have you set tha TPS and IAC?
    if you have not done a compression check and verified the valves are lashed correctly thats a good place to look , but only after the basics of ignition timing, spark, strength and fuel delivery are checked. your fuel pressure regulator , dirty injectors,clogged fuel filters loose connectors on injectors and sensors and ignition wire are frequently the cause as are corrosion on electrical connections, defective sensors., loose or broken vacuum lines.

    Id check for fuel pressure is steady and spark is consistent first and verify the spark plug condition as clear pictures of the plugs numbered by cylinder can give a great deal of info
    Id check for vacuum leaks , and loose battery connections and loose grounds

    http://forum.grumpysperformance.com/viewtopic.php?f=80&t=728

    viewtopic.php?f=70&t=202

    http://www.corvettephotographs.com/c4vettes/codes.htm

    viewtopic.php?f=50&t=9478&p=34812&hilit=sensors+camaro#p34812

    http://www.international-auto.com/fiat- ... gauges.cfm

    http://members.shaw.ca/corvette86/FuelS ... gnosis.pdf

    http://www.thirdgen.org/injectorswap injector swap

    http://www.thirdgen.org/tpimod2 IAC/ TPS

    viewtopic.php?f=56&t=495

    viewtopic.php?f=80&t=728&p=9217#p9217

    http://forum.grumpysperformance.com/viewtopic.php?f=32&t=168

    http://forum.grumpysperformance.com/viewtopic.php?f=32&t=596

    http://www.corvettebuyers.com/ecm.html

    viewtopic.php?f=36&t=8493&p=29779#p29779

    http://forum.grumpysperformance.com/viewtopic.php?f=32&t=3954

    viewtopic.php?f=50&t=609

    viewtopic.php?f=50&t=9478&p=34812&hilit=+ignition+coil+plug#p34812

    viewtopic.php?f=36&t=628&p=15040&hilit=opti#p15040

    http://corvetteactioncenter.com/tech/c4 ... Z1XqJwcC10

    viewtopic.php?f=55&t=606&p=1865&hilit=injector+ohms#p1865

    http://tech.corvettecentral.com/2007/08 ... diagnosis/

    viewtopic.php?f=55&t=635
    get out your shop manual and multi meter

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    read thru these links


    http://members.shaw.ca/agent86/Fuel Control And Delivery-8A.pdf
    http://members.shaw.ca/corvette86/EngineCranksButWontRun.pdf
    http://members.shaw.ca/corvette86/FuelSystemDiagnosis.pdf
    http://members.shaw.ca/corvette86/No-Service Engine Soon - Light.pdf
    http://members.shaw.ca/corvette86/SES Light On Steady.pdf
    http://members.shaw.ca/corvette86/Non Scan Diagnostic Circuit Check.pdf
    http://members.shaw.ca/corvette86/Engine to ECM Wiring Diagram 86.pdf
    http://members.shaw.ca/corvette86/Component Location View 86.pdf

    http://members.shaw.ca/corvette86/FuelSystemDiagnosis.pdf

    http://garage.grumpysperformance.co...questions-can-be-found-here.12892/#post-66934
    good info
    http://www.go-fast.org/z28/diagnostics.html

    http://www.corvetterecycling.com/category_s/63.htm
    this process of finding the cause of a problem, is basically a detailed check list and once you understand what your looking at and what its supposed to do after each components tested, is basically a simple procedure if you test, and eliminating potential sources until you narrow it down to the cause, where you prove it then re-place, repair or adjust as required.
    yes youll need to have some test equipment like, a shop manual, multi- meters and pressure gauges, timing lights etc. but its not that difficult
    [b]STEP ONE IS ALWAYS GET A FACTORY SHOP MANUAL, AND READ THE LINKS BELOW
    Verify fuel pressure,. by using a fuel pressure gauge on the shrader valve on the fuel rail, with a pressure gauge,
    Verify injector pulse by using a noid light, & spark at the plugs by using a spark tester.
    verify timing with a timing light
    pull the trouble codes and check all fuses
    [/B]
    http://www.mamotorworks.com/corvette.ht ... %20manuals

    http://www.helminc.com/helm/Result.asp? ... ted_media=

    http://www.factoryautomanuals.com/p-912 ... -only.aspx

    viewtopic.php?f=36&t=628&p=839#p839

    viewtopic.php?f=80&t=728&p=8392&hilit=codes_fuses#p8392

    http://members.shaw.ca/corvette86/FuelS ... gnosis.pdf

    viewtopic.php?f=32&t=304

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    viewtopic.php?f=2&t=3074&p=8144#p8144

    I frequently get questions about why cars, most of us own that are used mostly as weekend toys and not as daily transportation,cars that sit for a few days between use seem to be plagued with battery's that won,t stay charged, well ive gone over this a few times so heres a few links of related info
    viewtopic.php?f=36&t=3222&p=8575&hilit=test+alternator#p8575

    viewtopic.php?f=36&t=8493&p=37179&hilit=battery+drain#p37179

    viewtopic.php?f=48&t=10003&p=38749&hilit=battery+drain#p38749

    viewtopic.php?f=70&t=6857&p=22377&hilit=battery+drain#p22377

    viewtopic.php?f=70&t=2133&p=19303&hilit=battery+drain#p19303

    viewtopic.php?f=48&t=5144&p=14905&hilit=battery+drain#p14905

    http://forum.grumpysperformance.com/viewtopic.php?f=36&t=3453&p=26193&hilit=vats#p26193

    http://forum.grumpysperformance.com/viewtopic.php?f=36&t=520&p=645&hilit=vats+resistor#p645

    http://forum.grumpysperformance.com/viewtopic.php?f=36&t=63&p=31920&hilit=starter+rebuild#p31920

    http://forum.grumpysperformance.com/viewtopic.php?f=32&t=5926&p=18562&hilit=starter+rebuild#p18562

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    MAF SENSORS AND RELAYS ARE EASILY DAMAGED SO ALWAYS CHECK AND SUSPECT THOSE


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    BEFORE you start going nuts look at the obvious stuff first!
    CHECK THAT YOUR IAC and TPS sensors are set and adjusted correctly, set your ignition timing, make sure theres fuel in the gas tank,and theres no blown fuses and see if youve got a STEADY 37-40 psi on the fuel rail

    WHEN TESTING<be sure the fuel pressure gauge reads correctly by comparing it to a second test gauge, these fuel pressure gauges are frequently defective

    CHECK ALL YOUR FUSES WITH A MULTI METER
    check your fuse block with a meter , if the car won,t start, a common issue is blown injector fuses
    theres two fuses one controls the drivers side one controls the pass side injectors
    [​IMG]
    The secret of effective diagnosis and troubleshooting is to have a logical plan, and to follow it without skipping any steps.when ever you get into unexplained symptoms the answer remains the same....in every case,.... you drop back to the basics and do a few tests, (and until you gain experience you need the FACTORY SHOP MANUAL TO INDICATE THE TESTS, NEEDED AND THE EXPECTED RESULTS LISTED) get out a multi meter and verify every fuse is good, and you have 13 volts at the battery and youve got at least a 1/2 tank of fresh fuel, before you start chasing your tail, thinking about more complicated problems
    find the cause, you isolate, each function or system or malfunction to its related components then test, each individually, use of the shop manual is almost mandatory

    the next step is to get out your multi meter and carefully verify that ALL YOUR FUSES AND RELAYS WORK
    if they check out and its very likely that they WILL NOT DO SO, ID suggest checking the connections on oil pressure sensor at the rear of the block next to the distributor, if they look ok,ID replace the oil pressure sensor at the rear of the block next to the distributor, the fuel pump will only continue to run after the first few seconds and you only get voltage to the ignition if this sensor tells the CPU youve got 5 PSI of oil pressure during the start-up procedure
    [​IMG]

    Ive seen several corvettes with similar start, then stall issues that cleared up after replacing those sensors, Im reasonably sure the sensor INCORRECTLY and INTERMITTENTLY, indicate the oil pressure momentarily drops to ZERO causing the problem, but what IM sure of is that replacing the sensors cure the issue occasionally

    http://forum.grumpysperformance.com/viewtopic.php?f=32&t=1401&p=8895&hilit=start+sequence#p8895

    http://forum.grumpysperformance.com/viewtopic.php?f=32&t=2697

    http://forum.grumpysperformance.com/viewtopic.php?f=32&t=596

    viewtopic.php?f=56&t=495

    viewtopic.php?f=36&t=520&p=645&hilit=vats+resistor#p645

    viewtopic.php?f=70&t=270&p=1289#p1289

    http://www.73-87.com/7387garage/drivetrain/pkupcoil.htm

    viewtopic.php?f=80&t=728&p=8392&hilit=sensor+location#p8392

    http://www.aa1car.com/library/dis.htm

    viewtopic.php?f=36&t=628&p=6447&hilit=opti#p6447

    http://members.shaw.ca/corvette86/Component Location View 86.pdf

    verify your fuel pressure stays up in the 37-40 psi range without falling much after the cars shut off for at least 5 full minutes, and it should stay at 37-42 psi if the fuel rail pressure does drop off in the first few minutes its almost always a leaky injector or bad fuel pressure regulator, and check for vacuum leaks either could cause your symptoms, remember the fuel pressure should stay fairly consistent while the cars running regardless of how fast or long the throttles quickly blipped or held wide open,and be sure the throttle linkage and blades move smoothly and don,t bind or stick at any point in the movement arc.
    If you've got an early year TPI , that's designed to use a 9th cold start injector,check the cold start injector as its a potential problem source if its not working correctly.if your TPI won,t start, easily on the first try but starts easily on the second or third attempt, that's a very common indication of EITHER a leaking fuel pressure regulator (about 70% of the time), or less commonly a defective fuel pump(about 10%, of the time the pressures low or they leak internally) or leaking injector(s) (about 20% of the time)
    but it can also indicate a partly clogged fuel filter, or rarely air filter , and in rare cases a defective oil pressure sensor switch which won,t let the ignition work until theres more than 5 psi of oil pressure
    [​IMG]
    The secret of effective diagnosis and trouble shooting is to have a logical, well-ordered system. Following a logical step-by-step procedure will get you to the root cause of a problem quickly and efficiently. Repair manuals will have a diagnostic tree that goes in a logical progression. It will ask a question, usually yes or no, and depending on the answer will branch off in two or more directions. The last box in the tree will have the problem and how to correct it. The example shown is a simple one. A more complicated system will have branches going into specific tests and then have 2 or more branches from there depending on test results.
    first check your shop manual for the fuse and fuse able link locations
    fuses are located in several locations and fuse-able links near the battery


    start with testing the fuel pressure in the fuel rails, that symptom is frequently the result of a DEFECTIVE fuel pressure regulator,or leaky injectors ,or a blown fuse or the blown fuse-able link near the battery, get a fuel gauge, installed on the fuel rail , it should reach 40psi almost instantly when you try to start the car and maintain 40psi or more at the fuel rail for at least 15 minutes, on the early TPI theres a 9th injector thats used to richen the f/a mix that might be defective, latter TPI versions just added pulse width to the injectors during the first few minutes of run time. keep in mind,wet, loose, or broken electrical connectors or corrosion on connectors, is also possibly a cause of intermittent problems
    BTW To remove the connector from the injector, push carefully in the middle of the locking clip, with your thumb, This will make the sides, and tips move OUT WARD in their connector slots allowing the tips that hold the injector into the connector to slide out of the way from the injector body, and you can then pull the sides away. WATCH the locking clip - IT can and WILL come off and get lost, if your not careful




    IVE generally found no problem with any corvette LT1 or TPI efi if it will quickly build a minimum of 38-40PSI on start up and MAINTAIN at LEAST 38-40 psi for a MINIMUM of 10 minutes after the engines turned off, 40-42 lbs is what the factory tests want and expect so if your getting 38-40psi your pressure readings indicate a normal, perhaps even better than average pressure reading, and more than expected pressure retention,
    IF you suspect a TPI has a defective injector that's leaking or not flowing fuel,or partly clogged...You can also test this, to a degree, with a fuel pressure gauge
    you can install a fuel pressure gauge on the fuel rail, and turn on the ignition key then watch the gauge, it should jump to 37-42 psi then remain fairly steady for at least 5 minutes before gradually loosing pressure.
    If you can - and this is a pain in the butt to do, temporarily- remove the injectors. Leave them on the rail, but remove the rail. from the intake itself, This requires removing the majority of the TPI (P.I.T.A. but required).
    HERES HOW
    http://www.thirdgen.org/injectorswap

    Remove the rail, but leave it connected to the fuel lines.

    Next up, put a strip of cardboard under each bank. Then, have a buddy turn the ignition key on but not try to start the engine , you should hear the fuel pump run for 3 seconds while you look to see what happens. You should get an immediate spray of fuel.(all should be about equal and no injector remains dripping fuel) now have your buddy Turn off the key, while you watch closely to see which injectors are leaking.


    youll be amazed at what you can learn, by reading thru links and sub links provided below

    viewtopic.php?f=55&t=1241

    http://forum.grumpysperformance.com/viewtopic.php?f=32&t=596

    viewtopic.php?f=3&t=330&p=5167&hilit=start+sequence#p5167

    viewtopic.php?f=55&t=606&p=7969&hilit=noid+injector#p7969

    viewtopic.php?f=36&t=2412&p=7183&hilit=+oil+pressure+sensor#p7183

    viewtopic.php?f=55&t=606&p=7969&hilit=noid+injector#p7969

    viewtopic.php?f=55&t=3172&p=8673&hilit=fuel+filter#p8673

    viewtopic.php?f=32&t=2697

    http://members.shaw.ca/corvette86/FuelS ... gnosis.pdf

    viewtopic.php?f=62&t=3401&p=8972#p8972

    viewtopic.php?f=32&t=33

    viewtopic.php?f=50&t=609

    viewtopic.php?f=80&t=1470&p=3304&hilit=+fuel+corvette+pump#p3304

    viewtopic.php?f=32&t=33&p=41#p41

    viewtopic.php?f=55&t=635&p=12710#p12710

    viewtopic.php?f=80&t=728&p=9217&hilit=camaro+sensors#p9217

    viewtopic.php?f=32&t=10291&p=41713&hilit=start+sequence#p41713


    The first thing ID do is VERIFY the CAUSE, OF THE PROBLEM FOR THAT, THRU ISOLATING AND TESTING, COMPONENTS AND SYSTEMS , ignition spark should be bright blue and impressive, if its, weak,narrow, yellow or red theres a problem so research the cause, verify the coil and voltage
    always drop back to basics and verify all the sensors first,verify that the TDC on the damper and the timing tab, are correct,and you've set the ignition timing correctly, set the IAC and TPS sensor and check for vacuum leaks, verify the voltage, at the battery both running and before you start the car, it should be over 13 volts running and over 12.5 volts on just the battery.
    verify the plug gap is at about .045 inches (1.15mm) and the plugs are burning correctly, and set your ignition timing at 6
    btdc at about a 700-750rpm idle.
    use the timing light to verify the ignition advances as the rpms are increased, if its not advancing smoothly the distributor, might need work or the cpu might be defective

    owning a shop manual, a vacuum gauge and a V.O.M. meter and a timing light will be mandatory

    http://forum.grumpysperformance.com/viewtopic.php?f=32&t=1836

    A SHOP MANUAL IS ALMOST MANDATORY,

    THESE LINKS should help, EACH LINK PROVIDES DOZENS OF ANSWERS AND SUB LINKED TESTS ETC, since you can,t cure a problem until you understand whats wrong, read through the linked info

    viewtopic.php?f=80&t=728

    viewtopic.php?f=55&t=2055&p=5481#p5481

    viewtopic.php?f=55&t=1475&p=3325&hilit=testing+sensor#p3325

    viewtopic.php?f=55&t=1475&p=3325#p3325

    viewtopic.php?f=32&t=2701&p=6996#p6996

    viewtopic.php?f=55&t=1241&p=3037&hilit=+sensor#p3037

    http://tpiparts.net/85_89_maf_sensors/

    viewtopic.php?f=50&t=609&p=5672#p5672

    viewtopic.php?f=80&t=2019&p=5367#p5367

    viewtopic.php?f=32&t=304

    http://chevythunder.com/

    viewtopic.php?f=55&t=5307&p=15751&hilit=runners+gaskets+leak#p15751

    You will need some basic test equipment to perform your diagnosis.

    take notes your memory may not hold the exact numbers & results you need to refer back too.


    always drop back to the basics,
    get the starter to spin the engine
    verify theres compression
    verify your getting oil pressure
    verify the exhaust is not clogged, catalytic converters are not melted
    verify the cars fuel is clean and water free
    verify your getting fuel pressure
    verify your injectors are working
    verify your getting ignition spark at the plugs
    verify the valves are correctly adjusted
    verify the cams correctly indexed
    verify all the rockers are moving
    verify the distributor spins
    always drop back to basics

    have you verified TDC on the damper and timing tab?
    have you done a compression test?
    are all the spark plugs firing correctly?
    did you degree in the cam or just DOT-to-dot install it?
    whats your fuel pressure?
    have you verified the carbs float levels?
    does fuel run out the site holes at idle?
    are the needle& seat valves working correctly?
    whats your ignition timing?
    do you have voltage at the coil?
    whats your plenum vacuum?
    have you verified the engine got no vacuum leaks?
    whats the oil pressure?(did you check the dip stick?)
    have you adjusted the valves at idle?
    does the distributor timing advance with rpm increases?
    have you tried a different carb?
    what are the plugs gaped at?
    does this happen without an air filter?
    have you verified you've have functioning power valves?
    what jets are you using?
    is there visible fuel flow from the boosters?
    whats your battery voltage?
    whats your exhaust back pressure?
    are you totally sure the fuel free of water and fresh?
    have you pulled trouble codes?


    knowing whats going on and WHY can help , and a V.O.M. meter , code scanner, timing light, vacuum/fuel pressure gauge and a shop manually are basic tools

    MORE GOOD INFO

    http://www.corvettefever.com/techarticl ... index.html

    http://members.shaw.ca/corvette86/Compo ... w%2086.pdf

    http://members.shaw.ca/corvette86/FuelS ... gnosis.pdf

    http://chevythunder.com/lt1_electrical_page.htm

    http://chevythunder.com/Flow%20chart%20 ... rt%20Pages

    http://chevythunder.com/fuel%20injectio ... 20DIAGRAMS

    viewtopic.php?f=32&t=816

    viewtopic.php?f=55&t=2055

    viewtopic.php?f=62&t=3401


    Ill assume that youve verified the ignition timing PER THE SHOP MANUAL and that your getting spark plug electric SPARK,and your just having a slow or intermitant start most of the time, and it doesn,t seem to matter if the engines cold, warm or hot, and that at times it starts regularly but most of the time it requires several tries but once started it runs decently?

    Now by that IM referring to cars that when the ignition spins the engine over freely the engine takes its own sweet time catching, in most cases a simple test will indicate a common source of that problem.
    step one
    get in the car and turn the ignition key only far enought that the fuel pump runs, and pressurizes the fuel rails and shuts off, don,t turn the key to the point the engine spins on the starter, remove the key and repeat three times.
    step two
    on the fourth try on the start process attempt to start the car, by spining the engine over, if you find that it almost always starts under that condition its a strong indicator that the fuel rail pressure is dropping off and the prime suspect is the fuel pressure regulator, and a leaking diaphragm.
    you should see a minimum of 37 psi on a tpi, 40psi-42 psi on a LT1 at the fuel rails.
    replacing the OEM fuel pressure regulator with an adjustable aftermarket fuel pressure regulator will generally result in the problem being reduced or eliminated.
    other common potential problems are clogged/defective fuel filters or defective fuel pumps, fuel pump relays or fuses, leaky injectors fuel pump inlet screens or a bad fuel pump.


    drop back to the basics

    your shop manual will be a big help, and having a code reader and a vom meter will prove to be very useful.
    check that youve got 40-47 psi on an LT1 fuel rail and no less than 37 psi on a TPI fuel rail, injectors should read about 12-14 ohms resistance, spark plugs should look like they are burning correctly, the ignition wire should have similar resistance readings, the fuel pump should run once theres 5 psi or oil pressure and the engines spinning, read thru the links below carefully





    related useful linked info, you really should read thru as the sub links contain a ton of useful info

    viewtopic.php?f=32&t=764

    http://www.chevyhiperformance.com/howto ... index.html

    http://www.gmhightechperformance.com/te ... index.html


    viewtopic.php?f=32&t=596

    viewtopic.php?f=32&t=168

    viewtopic.php?f=36&t=676

    viewtopic.php?f=55&t=606

    viewtopic.php?f=32&t=33

    viewtopic.php?f=36&t=628&p=839#p839

    viewtopic.php?f=55&t=2614&p=7114&hilit=tpis+runner#p7114

    viewtopic.php?f=55&t=1115&hilit=+timing

    viewtopic.php?f=70&t=1015&p=1864&hilit=+light#p1864

    viewtopic.php?f=70&t=875

    TPI Torque Specifications

    Below are the torque specifications as designated by GM for Tuned Port Injection intakes. Please note that some specifications are in lb. ft., and some are in lb. in.

    Manifold to Runner Bolts 25 lb. ft.
    Runner to Manifold Bolts 25 lb. ft.
    Fuel Rail Attaching Bolts 15 lb. ft.
    Throttle Body Attaching Bolts 18 lb. ft.
    Throttle Position Sensor 18 lb. in.
    Idle Air Control Valve 13 lb. ft.
    Throttle Body Coolant Plate 27 lb. in.
    Throttle Body Cover Plate 30 lb. in.
    Power Brake Vacuum Fitting 108 lb. in.
    Fuel Line Nuts 20 lb. ft.
    Fuel Tube Bracket Bolt 25 lb. ft.
    Fuel Pressure Connection 115 lb. in.
    Pressure Regulator Base to Rail 44 lb. in.
    Pressure Regulator Bracket 44 lb. in.
    Outlet Tube to R/H Rail Retainer 44 lb. in.


    USE THE DATA BASE SEARCH FEATURE, Search FOR ANSWERS DON,T GUESS


    http://forum.grumpysperformance.com/viewtopic.php?f=57&t=853&p=1320#p1320

    http://forum.grumpysperformance.com/viewtopic.php?f=52&t=196

    http://forum.grumpysperformance.com/viewtopic.php?f=70&t=1411

    http://forum.grumpysperformance.com/viewtopic.php?f=70&t=967

    http://forum.grumpysperformance.com/viewtopic.php?f=50&t=1912

    http://forum.grumpysperformance.com/viewtopic.php?f=32&t=1148

    viewtopic.php?f=32&t=1773

    viewtopic.php?f=32&t=596

    viewtopic.php?f=32&t=303

    this info may help
    http://www.corvettebuyers.com/ecm.html

    http://www.aldlcable.com/
    don,t forget to pull trouble codes in your search for answers
    [​IMG]
    [​IMG]


    BTW SUSPECT A VACUUM LEAK?

    get out your oxy-acetylene torch or a propane torch, don,t light it but turn it on so gas is flowing and place the tip near any suspected leak points, while a buddy watches the tach, anytime the gas gets sucked thru a crack the rpms will jump higher in direct relation to the amount of extra fuel the engines getting, no, oil, fluid,or cruds or stains are left on the intake and its simple too do process


    take it a step at a time,set the fuel pressure at 40psi, check for vacuum leaks, and adjust the IAC and TPS and set the timing at 8 degrees per the manual,then drive it for 30 minutes to let the computer learn the conditions it operates in

    http://forum.grumpysperformance.com/viewtopic.php?f=32&t=168

    http://forum.grumpysperformance.com/viewtopic.php?f=70&t=875

    http://forum.grumpysperformance.com/viewtopic.php?f=50&t=821&p=1212&hilit=propane+leaks#p1212

    http://forum.grumpysperformance.com/viewtopic.php?f=32&t=1401

    viewtopic.php?f=50&t=10623&p=45691#p45691

    http://forum.grumpysperformance.com/viewtopic.php?f=70&t=1809
     
    Last edited by a moderator: Oct 14, 2017
  2. grumpyvette

    grumpyvette Administrator Staff Member

    Re: hard starting TPI, or LT1 vette

    this infos bound to be helpful at times

    the first step, in isolating a problems source on these c4 corvettes is almost always to pull trouble codes, and to grab the factory shop manual, so ID be looking at those first. youll want to have a muli meter and a fuel pressure gauge and it certainly won,t hurt to have a diagnostic code reader/scanner
    have you pulled trouble codes"
    what is the resistance reading on the new injectors?
    START WITH A BASIC TUNE UP, YOU MIGHT BE AMAZED AT HOW OFTEN WHAT YOU THINK IS A MAJOR ISSUE IS CURED WITH NEW SPARK PLUGS< IGNITION WIRES AND A NEW FUEL AND AIR FILTER AND SETTING THE IGNITION TIMING

    a very common problem on older TPI systems is a leaking fuel pressure regulator diaphragm resulting in excessive fuel in the plenum,as it gets sucked past the defective diaphragm , up into the plenum thru the vacuum line, the most likely source of that problem, is a ruptured or leaking fuel pressure regulator diaphragm thats allowing fuel to flow up the vacuum hose into the plenum, as its very unlikely all 8 injectors are leaking, that would account for the fuel pressure drop and all 8 cylinders showing excess fuel contamination
    [​IMG]
    replacement diaphragm
    [​IMG]
    stock FUEL PRESSURE REGULATOR
    [​IMG]
    [​IMG]
    ADJUSTABLE AFTERMARKET FUEL PRESSURE REGULATOR
    [​IMG]

    [​IMG]
    [​IMG]
    [​IMG]
    if you hear the fuel pump pressurize the fuel rails but the engine only starts than stalls, or fails to start, its frequently the fault of a defective oil pressure sensor

    ALWAYS TEST ALL YOUR INJECTORS OHMS RESISTANCE, WITH A MULTI METER, IF YOUR ENGINE RUNS BADLY ,INDIVIDUALLY< THEY SHOULD ALL BE VERY CLOSE TO EQUAL, ANY THAT ARE NOT NEED TO BE REPLACED

    low oil pressure or a defective oil pressure sensor will cut off your ignition
    [​IMG]
    both these sensors, located near the base of the distributor on the block, are known to fail & leak,oil at times, especially the smaller one with two blade connectors


    http://garage.grumpysperformance.com/index.php?threads/tpi-fuel-pressure-issue.10385/#post-42943
    [​IMG]


    [​IMG]
    http://chevythunder.com/
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    http://www.harborfreight.com/fuel-injec ... 92699.html
    HERES A FEW USEFUL, related bit of info and LINKS YOU MIGHT WANT TO LOOK THRU
    and yes they should all read very closely) then you need a noid kit for a G.M. fuel injection system, these are basically little lights that light as the injector pulse hits them that you plug into the injector harness,after you remove the harness from the injectors, they plug into the harness just like an injector, if you try to start the engine and they blink on and off the pulse is reaching the injectors thus proving that the injectors get the pulse, each injector should get a pulse and you should see each noid light flash, if you don,t theres an electrical or wiring issue, that must be addressed.
    injectors normal state is CLOSED they open only with a electric pulse, the duration of the pulse controls the volume of fuel flow
    carefully visually inspect your cars wire harness for corrosion ,loose or broken or shorting connectors or wiring, obviously getting the wrong electrical pulse, a grounded or shorted connector will cause problems.
    a NOID light can be used to test, the pulse is intermittent if plugged into the cars wire harness and its more likely the injector needs cleaning
    [​IMG]

    [​IMG]
    http://www.harborfreight.com/11-piece-n ... 97959.html

    [​IMG]
    reading thru a few links might be helpful
    step #1
    always ISOLATE AND VERIFY, TEST EVERYTHING ASSUME NOTHING!

    this cheap fuel pressure test gauge works ok, you just need to figure out how to tap into the fuel rail or line and that varies between years but certainly not a difficult issue to either remove a shrader valve and insert an adapter barb fitting or splice a TEE into a fuel line as a temp. test point, certainly any mechanic has an assortment of the common barb fittings required in a test kit

    [​IMG]
    [​IMG]
    as always a simple, step bye step approach where you verify the function or failure of each related component in the system before assuming any components working correctly is the smart route to take. never assume you know some component functions or is at fault until its tested carefully, and remember to verify proper voltage, resistance OHMS and ELECTRICAL GROUNDS
    [​IMG]
    THIS LINK WILL HELP
    http://members.shaw.ca/corvette86/FuelS ... gnosis.pdf
    now keep in mind the, fuel pump supplies fuel flow, the fuel pressure regulator restricts fuel from leaving the fuel rails untill pressure exceeds about 42 psi, each injector is basically just an electric solenoid that controls an internal valve in the injector thats NORMALLY in a closed position, until, the electrical pulse OPENS the injector, if you removed the electrical connectors the solenoid should remain firmly shut.
    (Id remove the aftermarket chip during testing as Ive seen a very high percentage of those aftermarket performance chips cause problems after a few weeks of run time as they seem overly prone to defects)

    [​IMG]
    [​IMG]
    the injector is supposed to be effectively a sealed valve controlling flow of fuel until voltage is applied forcing the solenoid to open the injectors internal fuel passage, and no fuel should be able to drain thru the orifice,if it does, even though the injectors may be new ID be strongly suspecting that debris in the tank or lines has entered the injectors ,water carrying micro crud or rust into the fuel line, and into the injector is preventing its full closure, as thats the only logical way fuel can pass thru a disconnected injector receiving no electrical current.
    it only takes a very small amount of rust/dust/crud in the fuel flowing thru an injector to let it leak or jam the pindle seat partly open, so don,t assume NEW injectors can swallow that sludge with impunity.
    the factory fuel filters are BARELY adequate for clean fuel

    the next step is to use a multi meter and verify injector resistance, it should be consistent within an OHM or two between all injectors depending on brand most c4 corvette injectors will read 12-15 OHMS resistance.
    Id then check the fuses and use a NOID test kit to verify the injector gets an electrical pulse at the electrical connector, remember each bank is separately fused on some year c4 corvettes
    Dirty or partially clogged injectors can show up in many ways and may include:

    - "Check Engine" light or cylinder misfire code
    - Poor idle
    - Light throttle surging or bucking
    - Denotation (knocking or pinging), causing possible engine damage
    - Low speed hesitation and surging issues
    - Emission problems
    - Loss of performance
    - Increased fuel consumption

    Leaky injectors can cause:

    - Hard starting, especially when hot
    - Poor idle
    - Emission problems
    - Increased fuel consumption
    - Exhaust odor

    [​IMG]

    Theres a great deal of related info, in these links
    swapping to a 200 amp alternator will frequently improve the operation of both the cars ignition and electric cooling fans

    https://www.summitracing.com/parts/tff-8173nep/applications/year/1996

    viewtopic.php?f=32&t=2697

    viewtopic.php?f=32&t=596

    viewtopic.php?f=55&t=6893&p=22467&hilit=58mm+throttle#p22467

    viewtopic.php?f=32&t=168

    viewtopic.php?f=32&t=302

    viewtopic.php?f=55&t=1378

    viewtopic.php?f=32&t=9493&p=34938#p34938

    viewtopic.php?f=80&t=728&p=9217&hilit=code+reader#p9217

    viewtopic.php?f=27&t=3096&p=8238&hilit=code+reader#p8238

    viewtopic.php?f=55&t=7310

    viewtopic.php?f=44&t=469&p=6061&hilit=code+reader#p6061

    viewtopic.php?f=36&t=63&p=8435&hilit=aldl#p8435

    viewtopic.php?f=32&t=6706&p=21505&hilit=noid#p21505

    viewtopic.php?f=55&t=606&p=7969&hilit=noid#p7969
    you really need to purchase a multi meter and a SHOP MANUAL and look thru the schematics
    without testing theres almost no way to locate the source of your problem,, testing will tell you


    http://www.helminc.com/helm
    http://www.factoryrepairmanuals.com...ice-manual-2-volume-set-original-shop-repair/
    your working at a huge dis-advantage if you don,t have a factory shop manual for your specific year car, and basic tools like a multi-meter, and vacuum /pressure gauge
    [​IMG]
    http://www.harborfreight.com/fuel-injection-pump-tester-92699.html
    [​IMG]
    http://www.harborfreight.com/5-in-1-dig ... 98674.html
    [​IMG]

    viewtopic.php?f=50&t=3110&p=12074&hilit=multi+meter#p12074

    [​IMG]

    [​IMG]

    [​IMG]
    http://www.harborfreight.com/5-in-1-dig ... 98674.html
    viewtopic.php?f=50&t=3110&p=12074&hilit=multi+meter#p12074

    [​IMG]

    [​IMG]
    LT1/LT4
    [​IMG]

    L98
    [​IMG]
    [​IMG]
    L98 TPI,

    [​IMG]
    [​IMG]
    the CORRECT ANSWER to what the cold start injector looks like that I get asked rather frequently, depends on what year, TPI you have, this is the early version like on the 1985 and it takes a unique injector, and its no longer available from chevy. they are also well know sources for vacume leaks

    [​IMG]
    L98 TPI, with turbos added

    Sensor Locations

    Sensor
    Location

    Engine Coolant Temperature Sensor. Front of engine, below Throttle Body.

    Engine Oil Temperature Sensor. Left rear of engine, just above the oil filter.

    Oil Pressure Sender/Switch. Top, left hand rear of engine.

    Fuel Quantity Sender. Top of fuel tank, beneath filler pipe escutcheon panel.

    MAT (Manifold Absolute Temperature Sensor). Underside of manifold air plenum at rear.

    Outside Temperature Sensor. Right side of engine, top right corner of radiator.

    In Car Temp Temperature Sensor. Coupe: above left seat near interior courtesy light, Convertible: center of cargo compartment lid.

    MAF (Mass Air Flow) Sensor. Front of engine ahead of throttle body.

    MAF Problems

    Faulty MAF sensors will normally light the check engine light on the drivers information center if the problem is constant and store a trouble code. If intermittent, a trouble code will still be stored as long as the battery is not disconnected.

    Normally, the problem is a poor connection at the sensor and wiggling the wires, unplugging and reinserting the connector will often cure the problem.

    A faulty MAF will normally cause a no start or difficult start condition and although you can eventually get the car into the "limp-home" mode in most cases, you need to attend to the problem ASAP.

    AC/Delco sensors can become intermittent or give false readings if the wires become contaminated as explained above.

    The MAF is a critical part of the emission control system and as such will cause the computer to react to problems very quickly, setting trouble codes and reducing performance in ways that cannot be ignored for long.

    MAF Mods

    The Bosch MAF is often modified by removing the two screens that are present in the front and rear of the cylinder. Removing these screens significantly increases the air flow through them and this results in more horsepower. Removing the screens is an old trick from the Corvette Challenge days in 1988 and 1989. It does work but is illegal in many states so be advised not to do anything that will get you arrested for a pollution violation.

    The AC/Delco MAF is not readily modified. It is what it is but since it is a larger diameter than the Bosch, it responds well to changing the air filter to a free flowing type such as the K&N filter."

    [​IMG]
    [​IMG]
    http://www.mamotorworks.com/corvette-c4 ... 6-893.html
    http://content.mamotorworks.com/pdf/601096.pdf

    Oxygen (O2) Sensor. Left side of engine, in exhaust pipe.(some years have two ,one on both sides)

    TPS (Throttle Position Sensor). Right side of throttle body at the front.


    Sensor Outputs:

    Sensor
    Measured Value

    Engine Coolant Temperature Sensor. 185 Ohms @ 210F, 3400 Ohms @ 68F, 7,500 Ohms @ 39 F.

    Engine Oil Temperature Sensor. 185 Ohms @ 210 F, 3400 Ohms @ 68 F, 7,500 Ohms @39 F.

    Oil Pressure Sender/Switch. 1 Ohms @ 0 PSI, 43 Ohms @ 30 PSI, 86 Ohms @ 60 PSI.

    Fuel Quantity Sender. 0 Ohms @ Empty, 45 Ohms @ 1/2 Full, 90 Ohms @ Full.

    MAT (Manifold Absolute Temperature Sensor). 185 Ohms @ 210 F, 3400 Ohms @ 70 F, 15,000 Ohms @ 40 F.

    Outside Temperature Sensor. 4400 Ohms @ 60 F, 2200 Ohms @ 85 F.

    In Car Temp Temperature Sensor. 4400 Ohms @ 60 F, 2200 Ohms @ 85 F.

    MAF (Mass Air Flow) Sensor. .4 Volts @ idle, 5 Volts @ Full Throttle.

    Oxygen (O2) Sensor. .1 Volt Lean Mixture, .9 Volt Rich Mixture.

    TPS (Throttle Position Sensor). .54 Volts Idle, ~ 5 Volts Full Throttle.

    IAC and TPS Adjustment
    http://www.thirdgen.org/tpimod2

    TPI Injector Swap
    http://www.thirdgen.org/injectorswap

    Throttle Body Coolant Bypass
    http://www.thirdgen.org/coolantbypass


    viewtopic.php?f=32&t=596
    [​IMG]
    you will want to PRINT the info from the private message... and this two minute test...

    would take a digital volt meter...

    set it to 20 volts DC scale...

    start the engine and turn on the headlights..

    1. test between the positive and the negative battery posts. 14.1 to 14.8 volts is expected.

    2. test between the negative battery post and the engine block. 0.04 volts is expected..

    3. test between the negative battery post and the body... 0.02 volts is expected..

    4. test between the Engine block and the body.. 0.02 volts is expected.

    if you get 0.00 on the last 3 tests.. change the meter setting to 2 volts DC scale.. and retest.. the last 3...

    this test takes about 2 minutes...

    post your results by test number..

    if you get more than the 0.04 or 0.02 volts on the display...

    you have a bad ground between those parts..
    why do this test.... bad grounds will stop any new car in its tracks...

    why... electrons flow from Negative to positive... if you loose a ground.. or it becomes intermittent.. you won't have any power for that circuit... just like a table light when the plug falls part way out of the wall... the light will go out..

    Re

    [​IMG]

    [​IMG]
    1987 TPI
    [​IMG]

    1991 TPI
    [​IMG]

    [​IMG]
    [​IMG]
     
    Last edited by a moderator: Sep 15, 2017
  3. grumpyvette

    grumpyvette Administrator Staff Member

    if you experience intermittent, times when the engine just won,t start or cuts out heres a few ideas,
    well,if it dropped trouble codes it would help,locate the problem of course,and on a car that old corrosion in electrical connectors or a bad ground or loose or corroded battery connections would be the first place I looked,
    it could be several causes and the next place that jumps to mind is a loose electrical connector or defective ignition switch, but a defective oil pressure switch,comes to mind also, because that's designed to cut off the fuel pump if oil pressure drops below 4 psi, if its defective it can cause problems,(yes Ive seen similar problems in the past)

    viewtopic.php?f=54&t=1396

    the VATS might be acting up,

    viewtopic.php?f=36&t=63&p=3403#p3403

    http://garage.grumpysperformance.com/index.php?threads/tpi-fuel-pressure-issue.10385/#post-42943

    we can rule out water in the fuel, because it would tend to run rough before & after it shut off at lease momentarily, you can rule out the CPU over heating because it can,t cool off in seconds, but Ive also seen HEI modules that were defective cause intermittent problems

    the first step is to use your inductive timing light to determine if you have spark at the plugs and your v.o.m. meter to see if the battery's producing over 13 volts when its hot, it may not be even ignition related? did you verify you have spark at the plugs?
    how about good fuel pressure?

    if your running an HEI ignition that's occasionally caused by a bad module.

    http://www.angelfire.com/empire/automot ... andtesting

    http://www.aa1car.com/library/us1296.htm

    viewtopic.php?f=50&t=3110&p=8296#p8296

    REPLACING A C4 CORVETTE BATTERY VIDEO
    http://www.youtube.com/watch?feature=pl ... 03-roWP2A#!

    Easy tests for HEI system:

    1. Test for power at the pink BAT terminal. You should have battery voltage w/ the key in the start and RUN positions.

    2. Connect the ground side of your test lamp to the battery POSITIVE cable. Probe the TACH terminal on the dist. cap while a helper attempts to start the engine. The test lamp should blink repeatedly as the engine cranks. No blink= bad module or pickup coil. Further testing is required to pinpoint the problem. Blink but no spark = bad ignition coil.

    3. Remove the cap & rotor. Remove the green & white leads from the module. Connect your ohmmeter to the green & white leads. You should have approx. 800-1500 ohms depending on the ambient temperature. Open circuit (infinite ohms) = bad pickup coil.

    Wiggle the green & white leads as you test. Ohm reading should remain constant if the leads are good. If the reading varies as the leads are wiggled, the pickup coil is bad. You'll often find broken pickup coil leads this way.

    4. DVOM (meter) still connected to green & white leads. Set your DVOM to AC VOLTS. Have a helper crank the engine as you watch the AC VOLTS reading. A good pickup coil will produce about 3V AC when cranking. Less than approx. 2V AC indicates a bad pickup coil.


    I really need more info, that could also be a carburetor or fuel system problem.

    did you use the dielectric tune up grease under the module... it is heat sink grease that allows the transfer of heat from the module to the aluminum housing... without out this proper grease the module will overheat and burn out...

    http://www.dimequarterly.tierranet.com/ ... h_hei.html

    viewtopic.php?f=50&t=609

    http://www.chevyhiperformance.com/techa ... index.html

    http://www.bronco.com/cms/node/25

    http://www.db-starter-alternator.com/St ... %20Motors/

    viewtopic.php?f=44&t=773&p=1123#p1123

    http://www.442.com/oldsfaq/ofign.htm

    http://www.ehow.com/how-does_4809570_tr ... butor.html

    viewtopic.php?f=32&t=10349&p=42530&hilit=relocating+sensor#p42530

    http://www.aa1car.com/library/2003/us80312.htm

    http://arrc.epnet.com/autoapp/9110/9110 ... System.htm

    [​IMG]

    http://www.chevelles.com/techref/ftecref5.html

    RAY QUAYLE POSTED THIS PICTURE

    [​IMG]

    link to more info on finding TDC and seating a distributor

    http://forum.grumpysperformance.com/viewtopic.php?f=70&t=967

    viewtopic.php?f=70&t=1411

    viewtopic.php?f=52&t=196

    viewtopic.php?f=32&t=1148

    viewtopic.php?f=32&t=1773

    http://www.classictruckshop.com/clubs/e ... ac/uum.htm

    read thru these threads and sub links, it almost always comes down to the basics, of compression, spark, fuel and timing
    verify you've got spark at the plugs, that your TDC marks on the damper are correct, and the cams correctly indexed and your distributors indexed correctly fuel pressure and no vacume leaks and your ignition timing and valve adjustment are correct

    this info may help
    http://www.corvettebuyers.com/ecm.html

    http://www.aldlcable.com/



    HEY GRUMPYVETTE?
    "
    Bad plug wires?
    Is there any way to check each wire other than to swap the whole set?"


    thats what one of things the OHMS setting on your v.o.m. meter, can be used for, good plug wire will read between 45-100 ohms per foot ,the ohms readings vary a great deal between manufacturers and different types of ignition wire so get a new section of similar wire about 2.5 feet long and use that to gauge a reasonable resistance reading on your meter, if your over 500 ohms you've usually got a defective plug wire and don,t forget to visually check for loose connections and burn marks,and to check the coil and its connections and its wire to the distributor.
    one old trick is to open your cars hood on a dark night or in a closed garage with low light conditions, and briefly start the engine while you, look for arcing while moving the ignition wires slightly.


    viewtopic.php?f=70&t=840&p=1986&hilit=+meter#p1986

    viewtopic.php?f=50&t=785&p=1337&hilit=+meter#p1337

    viewtopic.php?f=70&t=270&p=1289&hilit=+meter#p1289

    viewtopic.php?f=32&t=766&p=1179&hilit=+meter#p1179

    viewtopic.php?f=3&t=325&p=397&hilit=+meter#p397

    these links should save you some time diagnosing the problem

    http://members.shaw.ca/corvette86/FuelS ... gnosis.pdf

    http://members.shaw.ca/corvette86/Compo ... w%2086.pdf

    http://www.thirdgen.org/injectorswap

    http://www.thirdgen.org/tpimod2

    http://www.2carpros.com/kpages/first_things.htm

    http://www.ehow.com/how_2143018_test-fu ... e-car.html

    http://www.2carpros.com/dia/test_fuel_pressure.htm

    http://www.2carpros.com/dia/index.htm

    http://www.2carpros.com/dia/test_fuel_pressure.htm

    [​IMG]

    viewtopic.php?f=55&t=606&p=7969&hilit=noid+injector#p7969


    theres an excellent chance that one bank of injectors is not firing, check your fuses carefully (located on the pass side door dash frame)

    http://forum.grumpysperformance.com/viewtopic.php?f=55&t=606&p=7969&hilit=noid+injector#p7969

    http://forum.grumpysperformance.com/viewtopic.php?f=44&t=579&p=743&hilit=+infrared+tuning#p743

    http://forum.grumpysperformance.com/viewtopic.php?f=32&t=2697

    [​IMG]
    [​IMG]
    NATURALLY KNOWING HOW TO READ SPARK PLUGS AND AND use of a AIR FUEL RATIO METER AND USE OF AN IR TEMP GUN COMES IN VERY HANDY, as will a SHOP MANUAL MULTI METER AND PULLING TROUBLE CODES
    [​IMG]

    CHECK YOUR FUSES, YOUR SHOP MANUAL SHOULD HAVE A DIAGRAM FOR YOUR YEAR CORVETTE notice, that on this 1985-1987 fuse panel both #8 and #13 are injector fuses


    its always about the basics

    of spark (which you have)
    COMPRESSION
    CAM TIMING,
    (valve adjustment and having the cam degreed in correctly)
    IGNITION TIMING,
    (verify TDC and ignition curve)
    FUEL PRESSURE
    (38-42 psi at the fuel rails)
    FUEL SUPPLY (FLOW)
    (test the injector flow)
    (pull the trouble codes, and verify the battery voltage and grounds)

    http://www.corvettemagazine.com/2001/oc ... y/bat1.asp

    http://forum.grumpysperformance.com/viewtopic.php?f=50&t=609

    http://forum.grumpysperformance.com/viewtopic.php?f=32&t=2697

    http://forum.grumpysperformance.com/viewtopic.php?f=32&t=168

    viewtopic.php?f=70&t=875

    viewtopic.php?f=62&t=882&p=1390&hilit=+propane+leaks#p1390
     
    Last edited by a moderator: Apr 25, 2016
  4. grumpyvette

    grumpyvette Administrator Staff Member

    L98 TPI Engine Start Sequence
    http://www.corvettephotographs.com/c4vettes/l98.htm
    When you start an L-98 engine Corvette, a series of events take place that causes the engine to run. Knowing the sequence will help you troubleshoot no start conditions.

    Fuel Rail Pressurization:

    When you first turn the key to the “on” position, the fuel pump will run for 2 seconds pressurizing the fuel rails. There is a Shraeder valve on the passenger side fuel rail near the rear of the engine and if you measure the pressure there after the pump runs, you should see between 40-42 pounds of pressure. The reading will go to 38-40 pounds nominal once the engine is running.

    Initial Crank Action:

    If you then rotate the key to the start position (assuming the anti-theft system has not disabled the starter), the engine will rotate.

    Once the oil pressure has reached 4 PSI, the oil pressure switch will close allowing the fuel pump to run. (Note that you should have a black oil pressure switch/sender. It is mounted behind the distributor on the driver’s side and if it is not black, it is suspect due to a run of bad units that stayed in the GM parts pipeline for some time).

    The distributor will send a string of pulses to the ECM (Engine Control Module) in response to the engine being rotated by the starter. These pulses continue as long as the engine turns (both starting and running) and if they are not present, the engine will not run.

    ECM Reaction:

    If the ECM sees oil pressure greater than 4 PSI and the reference pulses from the distributor, it will energize the injector drivers which will begin pulsing the injectors on for 4 ms (milliseconds) periods. (In the L98, all injectors on one side of the engine fire at the same time followed by all injectors on the other side firing at the same time. On the LT-1, the injectors are fired individually at the appropriate time).
    some early c4 corvettes have the gauge and oil pressure switch on an adapter near the distributor base into the block

    theres a good deal of good and useful advise, in this thread but Id point out the
    sensor(s) next to the distributor, base ,could be a cause of a problem, because occasionally one of these starts acting up intermittently causing the fuel pump or ECM to stop working,or the VATS system, or the FUEL SUPPLY SYSTEM.

    [​IMG]

    [​IMG]
    [​IMG]
    if you hear the fuel pump pressurize the fuel rails but the engine only starts than stalls, or fails to start, its frequently the fault of a defective oil pressure sensor



    low oil pressure or a defective oil pressure sensor will cut off your ignition
    [​IMG]
    both these sensors, located near the base of the distributor on the block, are known to fail & leak,oil at times, especially the smaller one with two blade connectors




    heres some other possibility,s READ THRU THESE LINKS

    viewtopic.php?f=32&t=67&p=37351&hilit=start+sequence#p37351

    http://members.shaw.ca/corvette86/FuelS ... gnosis.pdf

    viewtopic.php?f=62&t=3401&p=8972&hilit=vats+resistor#p8972

    viewtopic.php?f=36&t=520&p=645&hilit=vats+resistor#p645

    viewtopic.php?f=32&t=33


    The ECM will also pull in the fuel pump relay in effect paralleling it electrically with the oil pressure switch. (If the fuel pump relay fails, you can still normally get the car to start and run unless you can’t make at least 4 PSI oil pressure. This is a “limp home mode” feature put in place to allow for a fuel pump relay failure).

    The ECM also monitors the TPS (Throttle Position Sensor mounted on the throttle body assembly) and wants to see .54 volts at this time. If it sees appreciably more than 0.54 volts, it will assume the engine is flooded and the driver has pressed the accelerator to the floor to clear the flooded condition and restrict the fuel flow as a result. (.54 volts during start and at idle from the TPS is very important to both starting and run performance.)

    Assuming the ignition module is good (meaning there is a spark of sufficient intensity to ignite the fuel), the engine will “catch”.

    Engine "Catches":


    When the engine catches, the MAF (Mass Air Flow sensor mounted just ahead of the throttle body) sends a signal to the ECM advising that air is flowing and also just how much air is being pulled through to the intake manifold. The ECM takes note of the amount of air being consumed and adjusts the injector pulse width to around 2.2 ms nominally so as to attain a proper air/fuel mixture to insure combustion. (This is how the 1985 through 1989 L-98 works. For information on the 1990 and 1991 L-98 variant, see the Note below).

    The engine should show an initial idle speed of around 900-1100 RPM and then slowly diminish to 600-700 RPM unless the air conditioner is on in which case it will run at around 800 RPM.

    If this does not happen, the Idle Air Mixture valve (located on the throttle body) may be misadjusted. Alternatively, there may be a leak in the intake manifold or another vacuum leak may be present. Listen for hissing sounds---there should be none.

    ECM Mode:

    The engine will now be in Open Loop mode meaning that the ECM is controlling the air/fuel mixture by referencing values stored in memory.

    Once the Oxygen sensor (mounted on the exhaust pipe) reaches operating temperature of several hundred degrees, the Manifold Air Temperature (MAT) sensor shows an intake air temperature of more than 140 degrees and the Engine Coolant Temperature (ECT) has reached 160 degrees, the computer will switch to closed loop mode meaning the Oxygen sensor’s output is examined along with the MAT and ECT outputs and the ECM adjusts the injector pulse widths (more “on time” or less “on time”) to constantly strive for a 14.7:1 air/fuel mixture which is the best mixture to hold down pollution.

    Note that prolonged idling can force the computer back into open loop mode.

    Note: In 1990, the MAF was eliminated from the engine in favor of a speed/density system. This system uses a sensor called the MAP sensor which measures the Manifold Absolute Pressure (hence the name MAP) and compares it with the atmospheric pressure outside the intake manifold. This information, coupled with the Manifold Air Temperature, Engine Coolant Temperature and Engine RPM is used by the ECM to determine the amount of air entering the cylinders. It is a different way of reaching the desired 14.7:1 air-fuel mixture ratio but functionally is like the MAF system in that the ECM uses the feedback to control the "on time" for the injectors.

    Corvette used this approach in the 1990 and 1991 L-98 engines and in the 1992 and 1993 LT-1 engines. With the 1994 model C4, they went back to the MAF system. Note that MAF based systems are far more accurate since they measure air flow directly whereas the MAP system infers air flow indirectly. A multitude of things can throw the calculation off and Corvette returned to the MAF system beginning with the 1994 C4 (with a MAP backup). From a troubleshooting standpoint, the MAP operation comes into the sequence the same place that the MAF does.
    1985-1989 systems used a Mass Air Flow (MAF) sensor.

    1990-1992 used a Manifold Absolute Pressure (MAP) sensor. Due to the unreliability of the MAF sensor, speed density systems (MAP sensor) are more desirable, and easier to install.

    Summary:

    If you have a no start condition or if the L-98 starts and then dies, check the above items in sequence to see if all the events are occurring as required.

    A Scan Tool makes this job much easier and is a highly recommended troubleshooting aid for these sorts of problems.
    http://www.austinthirdgen.org/mkportal/ ... wiring.gif

    vetteoz posted this bit of info

    if youve got a 1985-1986 with a cold start 9th injector
    and the car takes a long time to start if cold but starts easily when warm..
    Most likely the cold start injector is not working correctly
    The cold start switch ( brass unit with hex head on LHS in pic, GREEN CIRCLE ) only has power when engine is cranked over
    and if engine is cold enough , the switch sends power to the cold start injector located in the drv side of intake
    operating it to spray extra fuel ( like a choke on a carb car ).
    Check for 12V at switch when cranking.( any temp )
    Check for 12V out of switch and at CSI ( Cold start injector ) when cold cranking.
    If you have power there then most likely CSI itself is faulty

    [​IMG]


    [​IMG]
    COLD START INJECTOR ON EARLY TPI INTAKES

    http://garage.grumpysperformance.com/index.php?threads/replacing-a-c-4-fuel-filter.1470/#post-3304
    IF you have a more modern performance car that won,t start, you start with the basics also,
    have you pulled trouble codes yet?
    youll need a VOM meter and a list of trouble codes, and a shop manual sure will help!
    are you getting fuel pressure?
    have you checked the fuses for the injectors?
    have you checked for loose electrical connections, vacuum lines or defective sensors?
    have you used a noid light to test the injectors?
    what does the ohms resistance accross the unplugged injector read?
    how much?
    are you getting spark at the plugs?
    what color and is it strong?
    whats your oil pressure while cranking the car?
    can you pull the plugs and post CLEAR PICTURES with each cylinder numbered?
    whats the battery voltage?
    have you checked for vacume leaks?
    are you sure the distributor or coil is not wet or the connections loose?
    are you 100% sure theres clean fuel reaching the engine?
    have you replaced the fuel and air filters?
    was there any sound like a belt slipping or the engine running like the timing changed before this happened?
    have you done a compression check?
    have you taken off and carefully cleaned BOTH battery cable connections
    TECH SUPPORT LINES, before you get over your head ASK QUESTIONS

    look IM surely not trying to stop you from building a nice car but start with some basic skills and knowledge of the basic concepts

    start here

    buy these four books and read thru them then watch the cd a few times

    http://www.themotorbookstore.com/resmchstvi.html

    HOW TO BUILD MAX PERFORMANCE CHEVY SMALL BLOCKS ON A BUDGET by DAVID VIZARD

    .
    JOHN LINGENFELTER on modifying small-block chevy engines

    SMOKEY YUNICK,S POWER SECRETS

    then read thru this carefully

    http://www.rustpuppy.org/chp/

    then once youve got a few basics down proceed slowly and carefully and ask questions

    Holley
    Performance Products provides award-winning technical support via phone Monday through Friday, 8AM to 5PM CST @ 270 781-9741.

    Lunati
    technical support is availible by phone Monday through Friday 7AM to 5PM CST @
    662 892-1500.

    ERSON
    http://www.erson-cams.com/AskTechForm.aspx?BrandID=7
    http://www.erson-cams.com/pdf/Chevrolet.pdf

    CROWER cams
    http://www.crower.com/misc/contact.shtml

    CRANE CAMS
    http://www.cranecams.com/

    DART
    http://www.dartheads.com/
    \
    BRODIX
    http://www.brodix.com/
    please call us at 479-394-1075 for technical support

    TRICKFLOW
    http://www.trickflow.com/emain.asp

    EDELBROCK
    If you need to speak with an Edelbrock technician by phone, please call 1-800-416-8628 from 7:00am to 5:00pm, Monday-Friday, PST.

    ENGLE CAMS
    http://www.englecams.com/index.php
    Tel: (310) 450-0806
    Fax: (310) 452-3753

    ISKY CAMS
    http://www.iskycams.com/
    phone: 323.770.0930
    fax: 310.515.5730

    AIR FLOW RESEARCH
    http://www.airflowresearch.com/
    28611 W. Industry Drive
    Valencia, California, USA 91355
    tel: 877-892-8844
    fax:661-257-4462

    DEMON CARBS (Barry Grant Incorporated)
    http://www.barrygrant.com/
    Phone: (706) 864-8544
    Fax: (706) 864-2206

    ARIZONA SPEED/MARINE
    http://azspeed.stores.yahoo.net/c4col981.html

    MSD IGNITIONS
    http://www.msdignition.com/
    TECH LINE: 915-855-7123

    Shafiroff Race Engines
    http://www.ultrastreet.net/
    Toll Free: 800.295.7142 • Phone: 631.218.7530

    Ohio Crankshaft
    5453 SR 49 S
    Greenville, OH 45331
    Toll Free: 800-333-7113
    Local: 937-548-7113
    Fax: 937-548-4603
    http://www.ohiocrank.com/enginekits.html


    http://www.kevko.net/ (KEVKO OIL PANS)
    915 North Orient Street
    Fairmont, Minnesota 56031
    (507) 238-9633
    (800) 770-3557

    STEFS OIL PANS
    http://www.stefs.com/stefsindex.htm
    Stef's Performance Products
    693 Cross Street
    Lakewood, NJ. 08701
    Phone ( 732 ) 367- 8700
    fax: (732) 367-8793

    MELLING OIL PUMPS
    http://www.melling.com/
    Customer Service: 517-787-8172 ext: 125

    MOROSO
    http://www.moroso.com/default.asp
    call 203-458-0542, 203-458-0546

    MILODON
    http://www.milodon.com/index.asp
    Telephone
    Phone: (805) 577-5950
    Fax: 805-577-7540

    KB PISTONS
    http://www.kb-silvolite.com/index2.php
    1-800-648-7970

    ARP
    (BOLTS/STUDS)
    http://www.arp-bolts.com/
    800.826.3045

    REED CAMS
    http://www.reedcams.com/
    770.474.6664

    J&E PISTONS
    http://www.jepistons.com/
    714-898-9764

    SCAT CRANKS
    http://www.scatcrankshafts.com/
    310 370 5501

    Schneider Cams
    http://www.schneidercams.com/
    (619) 297-0227

    (TOOLS)
    http://www.goodson.com/
    800-533-8010

    http://www.quartermasterusa.com/
    847-540-8999

    hays clutches
    http://www.haysclutches.com/
    216.688.8300


    A few of MY favorite parts sources

    http://www.survivalmotorsports.com/
    248) 438-6900

    http://www.dougherbert.com/
    1-877-497-2787

    http://www.jegs.com/webapp/wcs/store...10001_10002_-1
    1800-345-4545

    http://www.summitracing.com/
    1800-230-3030

    http://www.midwestmotorsportsinc.com/
    1800-262-5033

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    Last edited by a moderator: Sep 9, 2016
  5. grumpyvette

    grumpyvette Administrator Staff Member

    EZELLM posted this info

    not getting fuel pressure on your 1982 crossfire this info might help

    "<QUOTE>
    The electric fuel pump draws high current, so it is not controlled directly by the ECM. Instead, The ECM controls a fuel pump relay which in turn controls system voltage to the fuel pump circuit.

    When the ignition is turned ON, before the starter is engaged, the ECM turns on the fuel pump relay for 2 seconds by providing ground. If the ECm does not receive ignition reference pulses from the ignition module within the 2 seconds, it shuts off the fuel pump relay until the engine is cranked. The ECM grounds the relay circuit as long as it receives ignition reference pulses. <UNQUOTE>

    Because the schematics in the books I have are really bad, I'm going to list the wiring in this circuit from a separate. . . . .

    ECM:
    ORN 340 - pins B1 and C16 receive power from the battery junction block through the fuse holder, and is also shared (common) to the oil pressure switch, and pin "E" (normally open) contacts of the fuel pump control relay.

    DK GRN/WHT 465 - pin A1 provides the 2 second, 12 VDC to pin "C", the positive side of the relay coil.

    BLK/WHT 450 - pin A12 provides ground to pin "B", the negative side of the relay coil.

    TAN/WHT 120 - pin B2 provides voltage monitoring for the fuel pump motor - this wire is tied to the positive side of the fuel pump, pin "A"(normally closed) contact of the relay, and the other side(from that mentioned above) of the oil pressure switch, and pin "D"(closed) contact of the relay.

    >>Just know that power is from the fuse panel through EITHER the pump relay OR the oil pressure switch, as they are in parallel with each other. the oil pressure switch is parallel to pins "E" and "D" of the relay. THAT'S what allows you to bypass the relay by jumping the oil pressure switch.<<
    theres two oil pressure sensors located near the drivers side of the distributor base on the early TPI engines
    [​IMG]

    [​IMG]
    [​IMG]
    [​IMG]
    IF you have a TPI or LT1-4 corvette its now 20 plus years old and if your having interment starting or engine missing or just cutting out issues a defective sensor is HIGHLY LIKELY first Id strongly suggest pulling the trouble codes

    then Id strongly suggest you change out the switch mounted near the distributor and its electrical connector, and the sensors related to the fuel pump and oil pressure even if they look and tested good as they are well known to cause intermittent problems

    and the fuel pump relay and fuel pump switch

    Sensor


    Measured Value
    Engine Coolant Temperature Sensor. 185 Ohms @ 210F, 3400 Ohms @ 68F, 7,500 Ohms @ 39 F.
    Engine Oil Temperature Sensor. 185 Ohms @ 210 F, 3400 Ohms @ 68 F, 7,500 Ohms @39 F.
    Oil Pressure Sender/Switch. 1 Ohms @ 0 PSI, 43 Ohms @ 30 PSI, 86 Ohms @ 60 PSI.
    Fuel Quantity Sender. 0 Ohms @ Empty, 45 Ohms @ 1/2 Full, 90 Ohms @ Full.
    MAT (Manifold Absolute Temperature Sensor). 185 Ohms @ 210 F, 3400 Ohms @ 70 F, 15,000 Ohms @ 40 F.
    Outside Temperature Sensor. 4400 Ohms @ 60 F, 2200 Ohms @ 85 F.
    In Car Temp Temperature Sensor. 4400 Ohms @ 60 F, 2200 Ohms @ 85 F.
    MAF (Mass Air Flow) Sensor. .4 Volts @ idle, 5 Volts @ Full Throttle.
    Oxygen (O2) Sensor. .1 Volt Lean Mixture, .9 Volt Rich Mixture.
    TPS (Throttle Position Sensor). .54 Volts Idle, ~ 5 Volts Full Throttle.

    Sensor Locations

    Sensor


    Location
    Engine Coolant Temperature Sensor. Front of engine, below Throttle Body.
    Engine Oil Temperature Sensor. Left rear of engine, just above the oil filter.
    Oil Pressure Sender/Switch. Top, left hand rear of engine.
    Fuel Quantity Sender. Top of fuel tank, beneath filler pipe escutcheon panel.
    MAT (Manifold Absolute Temperature Sensor). Underside of manifold air plenum at rear.
    Outside Temperature Sensor. Right side of engine, top right corner of radiator.
    In Car Temp Temperature Sensor. Coupe: above left seat near interior courtesy light, Convertible: center of cargo compartment lid.
    MAF (Mass Air Flow) Sensor. Front of engine ahead of throttle body.
    Oxygen (O2) Sensor. Left side of engine, in exhaust pipe.
    TPS (Throttle Position Sensor). Right side of throttle body at the front.
    this might help also

    viewtopic.php?f=32&t=596

    http://www.autozone.com/shopping/repair ... 528008fdea

    viewtopic.php?f=56&t=8401&p=29318&hilit=clogged+cats#p29318

    http://garage.grumpysperformance.com/index.php?threads/replacing-a-c-4-fuel-filter.1470/#post-3304


    [​IMG]

    [​IMG]
    1987 TPI
    [​IMG]

    1991 TPI
    [​IMG]
     
    Last edited by a moderator: May 6, 2016
  6. grumpyvette

    grumpyvette Administrator Staff Member


    HEY GRUMPYVETTE
    My vette Won't Start until Oil pressure builds to 50
    Just picked up an 85 vette. When cold, car will not start until oil pressure builds up to 45-55 pounds. It will start firing when pressure reaches 45-55 and finally starts. You cannot hear fuel pump running when you turn the key. Once fired off it usually fires right up but it has started to die at times after it is warmed up. Sometimes if it is shut off to go in a store and you come right back out it just turns over and won't fire. If I wait a few minutes it then immediately fires up. Today it died twice on the way home. Waited for a couple minutes each time and it would immediately fire and drive for a few minutes again.

    when it is hot and won't start, you cannot hear fuel pump then either when you cycle the key on and off. The engine is oil is hot and pressure gauge reads 30 to 40 pounds cranking when it won't start. Can't build pressure to see if that is the reason it won't start when hot. Just weird that it will immediately fire if I wait a few minutes.


    CROSSFIRE
    [​IMG]

    VETTEOZ posted this answer and its to the point
    "Fuel pump oil pressure switch faulty ?
    Should close @ 4 psi oil pressure and run the pump
    OP switch is a backup to the pump relay should relay fail ; allows motor to start once oil pressure up and keep running.
    If relay not working and OP switch intermittent could be cause of your problems

    In any case pump should prime for 2 sec when key 1st turned on.
    Check fuel pump relay and connector; commonly go bad with age.

    To prove a point ; put 12V on terminal G of the ALDL connector.That will run the pump fulltime.
    Try starting with pump running and see if anything different "
     
    Last edited: May 18, 2015
  7. grumpyvette

    grumpyvette Administrator Staff Member

    1985 ECM Codes
    Code #12: Normal No Codes.
    Code #13: Open Oxygen Sensor Circuit.
    Code #14: Coolant Sensor Circuit Low.
    Code #15: Coolant Sensor Circuit High.
    Code #21: Throttle Position Sensor High.
    Code #22: Throttle Position Sensor Low.
    Code #23: Manifold Air Temperature Circuit High.
    Code #24: Vehicle Speed Sensor.
    Code #25: Manifold Air Temperature Circuit Low.
    Code #32: EGR System Failure.
    Code #33: Mass Air Flow Sensor High.
    Code #34: Mass Air Flow Sensor Low.
    Code #36: Mas Air Flow Sensor Burn-Off Function Fault.
    Code #41: Cylinder Select Error.
    Code #42: Electronic Spark Timing.
    Code #43: Electronic Spark Control.
    Code #44: Lean Exhaust indication.
    Code #45: Rich Exhaust Indication.
    Code #46: Vehicle Anti Theft Fault.
    Code #51: Faulty Mem-Cal.
    Code #52: Fuel Calpak Missing.
    Code #52: (1990-91 Corvette Only): Engine Oil Temperature Sensor Low.
    Code #53: System Over Voltage.
    Code #54: Fuel Pump Circuit Low Voltage.
    Code #55: Defective ECM.
    Code #62: Engine Oil Temperature Sensor Circuit High.

    GM OBD-1 Diagnostic Trouble Codes
    For 1995-previous model year EFI-equipped GM vehicles. NOTE: Some codes not supported on all models, consult your specific vehicle's service manual for the correct trouble code list and description for your application.
    DTC - 12 No distributor reference pulse (diagnostic test active)
    DTC - 13 Oxygen sensor circuit open or no activity
    DTC - 13 Left bank O2 sensor circuit open or no activity
    DTC - 14 Engine coolant temp sensor error (high temp indicated)
    DTC - 15 Engine coolant temp sensor error (low temp indicated)
    DTC - 16 System voltage too low
    DTC - 17 Camshaft position sensor error
    DTC - 21 Throttle Position sensor error (signal high)
    DTC - 22 Throttle position sensor error (signal low)
    DTC - 23 Intake air temp sensor error (low temp indicated)
    DTC - 24 Vehicle speed sensor error (open circuit or no activity)
    DTC - 25 Intake air temp sensor error (high temp indicated)
    DTC - 26 Quad Driver Module (QDM A) error
    DTC - 28 Auto transmission range pressure switch error
    DTC - 31 Wastegate solenoid circuit error
    DTC - 31 Gear Position Switch (PRNDL) error
    DTC - 32 EGR system failure
    DTC - 33 MAP sensor circuit error (signal high indicating low vacuum)
    DTC - 34 MAP sensor circuit error (signal low indicating high vacuum)
    DTC - 35 IAC problem or idle error
    DTC - 36 MAF sensor error
    DTC - 36 24x Crankshaft position sensor circuit error
    DTC - 36 4T60-E Shifting Error
    DTC - 37 TCC brake switch circuit error
    DTC - 38 TCC brake switch circuit error
    DTC - 39 Clutch switch circuit error
    DTC - 39 TCC error
    DTC - 41 Ignition control error
    DTC - 41 MEM-CAL error
    DTC - 41 C³I Cam Sensor Signal error
    DTC - 42 Ignition bypass circuit error
    DTC - 43 Knock sensor error
    DTC - 44 Oxygen sensor error (lean condition indicated)
    DTC - 44 Left bank O2 sensor error (lean condition indicated)
    DTC - 45 Oxygen sensor error (rich condition indicated)
    DTC - 45 Left bank O2 sensor error (rich condition indicated)
    DTC - 46 Pass-Key II (VATS) system error - circuit out of freq range
    DTC - 47 UART (serial data) circuit error
    DTC - 51 PROM error
    DTC - 51 Incorrect MEM-CAL
    DTC - 52 Fuel cal-pak incorrect or missing
    DTC - 53 System voltage too high
    DTC - 53 Digital EGR Valve solenoid 1 error
    DTC - 54 Fuel pump circuit low voltage
    DTC - 54 Digital EGR Valve solenoid 2 error
    DTC - 55 ECM error
    DTC - 55 Digital EGR Valve solenoid 3 error
    DTC - 56 Quad Driver Module (QDM B) error
    DTC - 57 Boost Control error
    DTC - 58 Trans fluid temp sensor circuit error (low voltage)
    DTC - 58 VATS system error
    DTC - 59 Trans fluid temp sensor circuit error (high voltage)
    DTC - 61 A/C system performance
    DTC - 63 Right bank O2 sensor circuit error
    DTC - 63 MAP sensor circuit signal voltage high (low vacuum indicated)
    DTC - 64 Right bank O2 sensor lean exhaust indicated
    DTC - 64 MAP sensor circuit signal voltage low (high vacuum indicated)
    DTC - 65 Right bank O2 sensor rich exhaust indicated
    DTC - 66 A/C pressure sensor circuit error (low pressure indicated)
    DTC - 67 A/C pressure sensor circuit error
    DTC - 68 A/C clutch relay circuit error (shorted to ground)
    DTC - 69 A/C clutch relay circuit error (open circuit indicated)
    DTC - 69 A/C high pressure switch error
    DTC - 70 A/C pressure sensor circuit error (high pressure indicated)
    DTC - 71 A/C evaporator temp sensor circuit error (low temp indicated)
    DTC - 72 VSS signal circuit error
    DTC - 73 A/C evaporator temp sensor circuit error (high temp indicated)
    DTC - 75 Digital EGR solenoid #1 circuit error
    DTC - 76 Digital EGR solenoid #2 circuit error
    DTC - 77 Digital EGR solenoid #3 circuit error
    DTC - 79 Transmission fluid overtemp
    DTC - 80 Transmission component slipping
    DTC - 82 3x Crankshaft position sensor circuit error
    DTC - 85 PROM error
    DTC - 86 A/D error
    DTC - 87 EEPROM error (flash memory error)
    DTC - 90 TCC error
    DTC - 93 Transmission pressure control solenoid circuit error
    DTC - 96 Transmission system voltage low
    DTC - 98 Invalid PCM program
    DTC - 99 Invalid PCM program

    1985 to 1991 Computer Codes



    Code #12: Normal No Codes.
    Code #13: Open Oxygen Sensor Circuit.
    Code #14: Coolant Sensor Circuit Low.
    Code #15: Coolant Sensor Circuit High.
    Code #21: Throttle Position Sensor High.
    Code #22: Throttle Position Sensor Low.
    Code #23: Manifold Air Temperature Circuit High.
    Code #24: Vehicle Speed Sensor.
    Code #25: Manifold Air Temperature Circuit Low.
    Code #32: EGR System Failure.
    Code #33: Mass Air Flow Sensor High.
    Code #34: Mass Air Flow Sensor Low.
    Code #36: Mas Air Flow Sensor Burn-Off Function Fault.
    Code #41: Cylinder Select Error.
    Code #42: Electronic Spark Timing.
    Code #43: Electronic Spark Control.
    Code #44: Lean Exhaust indication.
    Code #45: Rich Exhaust Indication.
    Code #46: Vehicle Anti Theft Fault.
    Code #51: Faulty Mem-Cal.
    Code #52: Fuel Calpak Missing.
    Code #52: (1990-91 Corvette Only): Engine Oil Temperature Sensor Low.
    Code #53: System Over Voltage.
    Code #54: Fuel Pump Circuit Low Voltage.
    Code #55: Defective ECM.
    Code #62: Engine Oil Temperature Sensor Circuit High.



    1992 to 1993 DTC Computer Codes



    Code #12: Normal No Codes.
    Code #13: Left Oxygen Sensor Circuit.
    Code #14: Coolant Temperature Sensor Circuit High.
    Code #15: Coolant Temperature Sensor Circuit Low.
    Code #16: Opti-Spark Ignition Timing System.( Low Pulse)
    Code #21: Throttle Position Sensor Circuit High.
    Code #22: Throttle Position Sensor Circuit Low.
    Code #23: Intake Air Temperature Sensor Circuit Low.
    Code #24: Vehicle Speed Sensor Circuit.
    Code #25: Intake Temperature Sensor Circuit High.
    Code #26: Quad-Driver Module #1 Circuit.
    Code #27: Quad-Driver Module #2 Circuit.
    Code #28: Quad-Driver Module #3 Circuit.
    Code #32: Exhaust Gas Recirclation Circuit.
    Code #33: Manifold Absolute Pressure Sensor Circuit Low.
    Code #34: Manifold Absolute Pressure Sensor Circuit High.
    Code #36: Opti-Spark Ignition Timing System. (High Resolution Pulse.)
    Code #41: Electronic Spark Timing Circuit Open.
    Code #42: Electronic Spark Timing Circuit Grounded.
    Code# 43: Electronic Spark Control Circuit.
    Code #44: Left Oxygen Sensor Circuit Lean.
    Code #45: Left Oxygen Sensor Circuit Rich.
    Code #51: Mem-Cal Error.
    Code #52: Engine Oil Temperature Sensor Circuit Low.
    Code #53: System Voltage.
    Code #55: Fuel Lean Monitor.
    Code #56: Vacuum Sensor Circuit.
    Code #61: Secondary Port Throttle Valve System.
    Code #62: Engine Oil Temperature Sensor Circuit High.
    Code #63: Right Oxygen Sensor Circuit Open.
    Code #64: Right Oxygen Sensor Circuit Lean.
    Code #65: Right Oxygen Sensor Circuit Rich.
    Code #66: A/C Pressure Sensor Circuit Open.
    Code #67: A/C Pressure Sensor Circuit. (Sensor or A/C Clutch Circuit Problem)
    Code #68: A/C Relay Circuit Shorted.
    Code #69: A/C Clutch Circuit.
    Code #72: Gear Selector Switch Circuit.


    1994 to 1996 DTC Computer Codes
    DTC #11: Malfunction Indicator Lamp Circuit.
    DTC #13: Bank #1 Heated Oxygen Sensor #1 Circuit:
    DTC #14: Engine Coolant Temperature Sensor Circuit Voltage Low.
    DTC #15: Engine Coolant Temperature Sensor Circuit Voltage High.
    DTC #16: Distributor Ignition System Low Pulse.
    DTC #18: Injector Circuit.
    DTC #21: Throttle Position Sensor Circuit Voltage High.
    DTC #22: Throttle Position Sensor Circuit Voltage Low.
    DTC #23: Intake Temperature Sensor Circuit Voltage High.
    DTC #24: Vehicle Speed Sensor Circuit.
    DTC #25: Intake Air Temperature Sensor Circuit Voltage Low.
    DTC #26: Evaporative Emission Canister Purge Solenoid Valve Circuit.
    DTC #27: EGR Vacuum Control Signal Solenoid Valve Circuit.
    DTC #28: Transmission Range Pressure Switch Assembly Fault.
    DTC #29: Secondary Air Injection Pump Circuit.
    DTC #32: Exhaust Gas Recalculation.
    DTC #33: Manifold Absolute Pressure Sensor Circuit High.
    DTC #34: Manifold Absolute Pressure Sensor Circuit Low.
    DTC #36: Distributor Ignition System High Pulse.
    DTC #37: Brake Switch Stuck On.
    DTC #38: Brake Switch Stuck Off.
    DTC #41: Ignition Control Circuit Open.
    DTC #42: Ignition Control Circuit Shorted.
    DTC #43: Knock Sensor Circuit.
    DTC #44: Bank 1 LF Heated Oxygen Sensor #1 Circuit Lean.
    DTC #45: Bank 1 LF Heated Oxygen Sensor #1 Circuit Rich.
    DTC #47: Knock Sensor Circuit Or Module Missing.
    DTC #48: Mass Air Flow Sensor Circuit.
    DTC #50: System Voltage Low.
    DTC #51: EEPROM Programming Error.
    DTC #52: Engine Oil Temperature Sensor Circuit Voltage Low.
    DTC #53: System Voltage Low.
    DTC #55: Fuel Lean Monitor.
    DTC #58: Transmission Fluid Temperature Sensor Circuit Low.
    DTC #59: Transmission Fluid Temperature Sensor Circuit High.
    DTC #62: Engine Oil Temperature Sensor Circuit Voltage Low.
    DTC #63: Bank 2 RF Heated Oxygen Sensor #1 Circuit Open.
    DTC #64: Bank 2 RF Heated Oxygen Sensor #1 Circuit Lean.
    DTC #65: Bank 2 RF Heated Oxygen Sensor #1 Circuit Rich.
    DTC #66: A/C Refrigerant Pressure Sensor Circuit Open.
    DTC #67: A/C Pressure Sensor Circuit Sensor or A/C Clutch.
    DTC #68: A/C Relay Circuit.
    DTC #69: A /C Clutch Circuit.
    DTC #70: A/C Clutch Relay Driver Circuit.
    DTC #72: Vehicle Speed Sensor Loss.
    DTC #73: Pressure Control Solenoid Circuit Current Error.
    DTC #74: Traction Control System Circuit Low.
    DTC #75: Transmission System Voltage Low
    DTC #77: Primary Cooling Fan Relay Control Circuit.
    DTC #78: Secondary Cooling Fan Relay Control Circuit.
    DTC #79: Transmission Fluid Overtemp.
    DTC #80: Transmission Component Slipping.
    DTC #81: Transmission 2-3 Shift Solenoid Circuit.
    DTC #82: Transmission 1-2 Shift Solenoid Circuit.
    DTC #83: Torque Converter Solenoid Voltage High.
    DTC #84: 3-2 Control Solenoid Circuit.(Auto Only).
    DTC #84: 2nd And 3rd Gear Blockout Relay Control Circuit.
    DTC #85: Transmission TCC Stock On.
    DTC #90: Transmission TCC Solenoid Circuit.
    DTC #91: One To Four Upshift Lamp(Manual Only).
    DTC #97: VSS Output Circuit.
    DTC #98: Tachometer Output Signal Voltage Wrong.
     
  8. grumpyvette

    grumpyvette Administrator Staff Member

    "HERES AN INTERESTING PROBLEM FROM A DIFFERENT SITE THAT I ANSWERED"

    " HEY GRUMPYVETTE, ?
    IM REALLY PISSED OFF! this is the second fuel pump Ive replaced, the fuel rails get 45 psi when I start the car but after 15 minutes drive time the car stalls, if I let it sit for 15 minutes I can drive it for 15-20 minutes and then it stalls, its fuel pressure, it drops to less than 15 psi after about 15 minutes,and the fuel tanks got a good bit of pressure when the gas caps removed if that helps, any ideas?"




    pressure is a measure of RESISTANCE TO FLOW, Id have replaced the fuel filter and checked sensors and pulled trouble codes,assuming you replaced the fuel pump correctly it sounds like its a sensor or vacuum or f/p regulator issue,naturally pulling trouble codes and having a shop manual, multi meter and vacuum gauge will help locate the problem.
    your symptoms sound like a defective fuel pressure regulator, or the vacuum line controlling the fuel pressure regulator may be leaking or plugged or disconnected , or the evap systems defective or a sensor may be defective, to me, but a few tests will tell you the source of the problem so test don,t guess, get a shop manual and pull codes and carefully inspect the vacuum lines and test the sensors


    [​IMG]
    [​IMG]



    related threads and helpful info

    http://members.shaw.ca/corvette86/FuelS ... gnosis.pdf

    viewtopic.php?f=32&t=33

    viewtopic.php?f=55&t=1241

    viewtopic.php?f=80&t=728&p=9217&hilit=sensor+ohms#p9217

    viewtopic.php?f=32&t=596

    viewtopic.php?f=56&t=3049&p=8053&hilit=oxygen+sensors#p8053

    http://garage.grumpysperformance.co...rvette-after-battery-failed.10291/#post-41710



    BTW it turned out the guy had a melted vacuum line under the plenum causing all the problems




    that could easily be a symptom of a loose electrical ground , bad battery connection or low battery, defective alternator, loose serpentine belt, under drive crank pulleys can all effect this, Id suggest cleaning the battery terminals and checking grounds, gauge readings depend on current flow, if the current draw rate increases past the alternators ability to supply current your lights dim, gauges read funny etc.
    these links should help

    viewtopic.php?f=50&t=3110&p=21360&hilit=multi+meter#p21360

    viewtopic.php?f=36&t=3222&p=8575&hilit=test+alternator#p8575

    viewtopic.php?f=50&t=609&p=5672&hilit=test+alternator#p5672

    viewtopic.php?f=48&t=4729&p=12842&hilit=battery+connection#p12842

    viewtopic.php?f=70&t=3901&p=10343&hilit=battery+terminal#p10343

    viewtopic.php?f=44&t=3401&p=8972&hilit=battery+terminal#p8972

    viewtopic.php?f=36&t=317&p=13210&hilit=battery+connection#p13210

    viewtopic.php?f=80&t=728&p=9217&hilit=battery+connection#p9217

    viewtopic.php?f=70&t=3504&p=9219&hilit=battery+connection#p9219

    viewtopic.php?f=32&t=1401&p=5445&hilit=test+alternator#p5445
     
    Last edited by a moderator: Sep 15, 2017
  9. grumpyvette

    grumpyvette Administrator Staff Member

    "HEY GRUMPY? my 1992 vettes been sitting in the garage for over two years, I added fuel system conditioner to the tanks fuel before I parked it, I have since drained the fuel in that tank and replaced the fuel in the tank, with fresh fuel, I did an oil change, replaced the fuel filter and replaced the battery and spark plugs, it spins over now but won,t start , any ideas??

    obviously pulling trouble codes will help, and yes Id check the OPTI ignition, or HEI ignition timing and sensors, Heres a bunch of related info to help you isolate the problem


    http://www.youtube.com/watch?feature=pl ... oXLUqE4Sf0

    viewtopic.php?f=36&t=628&p=6447&hilit=opti#p6447

    viewtopic.php?f=32&t=1401

    viewtopic.php?f=32&t=2697

    viewtopic.php?f=32&t=2697&p=18904&hilit=sensors#p18904

    viewtopic.php?f=80&t=728&p=8392&hilit=sensors#p8392

    viewtopic.php?f=32&t=596

    viewtopic.php?f=32&t=33

    If I was on site I could test far faster than type what to look for, but first step is pull trouble codes,look for loose vacuum lines and loose electrical connectors, then get out the multi meter and verify you have 13-14 volts at the battery while the engine cranks, that all the fuses test good, and a noid light test shows the injectors firing, and you get ignition spark at the plugs.
    next you want to verify oil pressure is at least 10psi while cranking,and fuel pressure stays at about 40psi
    it always comes back to the basics,
    are you getting fuel pressure?
    do you have compression?
    are ALL the plugs firing?
    are there trouble codes?
    are all the injectors working?
    what the voltage as your cranking?
    do you hear the fuel pump run?
    HAVE you checked for vacuum leaks, loose electrical connections?
    have you done a compression check?
    have you checked the exhaust back pressure?


    I just had a guy have his car towed over to have me look at it, it was a 1987 TPI corvette, it would not start, and when it did act like it wanted to for a second or so it would almost catch and run but would not stay running for more than a 1/2 second, I checked ignition timing and for spark and that was fine.
    your best route is going thru a step by step check list, don,t guess verify each system functions

    [​IMG]
    you can,t make intelligent choices with out knowing the facts about exactly how things are supposed to work, and testing to verify that they are working currently as they were designed too or not
    [​IMG]
    so I used my shrader valve tool

    [​IMG]
    to remove the center valve section
    [​IMG]

    BTW vinyl tube should never be used as fuel line for any longer than a quick test as it gets brittle when subjected to fuel and engine heat over time and becomes a fire hazard

    I placed a 3 foot section of clear vinyl tube over the now open shrader valve so fuel would would exit the fuel rail, and flow into a clear quart container, so I could see if there was water mixed in the fuel,...all I got was a bunch of bubbling fuel and mostly air so I realized the fuel supply was not providing significant fuel pressure,or fuel flow volume. the fuel gauge indicated a 1/4 tank but adding 5 gallons instantly got solid fuel pressure and flow, replacing the shrader valve interior and trying to start the car, it fired right up, the major engine problem was, simply that he was flat out of fuel and the gauge is defective

    if you suspect the injectors have gone bad or are locked up and your test with a NOID LIGHT TEST KIT shows the injectors are getting the required pulse from the wiring and the injectors have the required ohms resistance and you have the fuel rail pressure, but your not getting fuel, and you are getting ignition spark,its always a case of isolate and test, that finds the cause, and you start with the basics of trouble codes , and fuel, compression, spark, and timing.
    old school testing still works and if you swap the current injectors out for different injectors and nothing changes you have a good indication its not the injectors causing the problem, now the problem with that course of action is that new injectors tend to cost $300-$600 a set for 8 , thus a bit of creativity is used,
    If it was my car Id have done a bit of research and located a list of cars that had compatible injectors that could be swapped in, then visit a salvage yard with a easily portable tool kit and a multi meter and found at least 16 injectors , that I could pull that passed the ohm meter test for use in testing the car, by simply swapping out the injectors wholesale after very carefully cleaning the salvage yard supplied injectors.(obviously the price will vary so ask before you go thru the effort but Ive generally paid $60-$80 for a set of 8 used injectors which I test with an ohms meter before I remove them, and having a spare set is certainly worth that)

    heres a link to swapping injectors
    http://www.thirdgen.org/injectorswap

    youll find a great deal more detailed info in the links and sub links listed below

    viewtopic.php?f=32&t=1401

    viewtopic.php?f=55&t=1241&p=2648&hilit=noid#p2648

    viewtopic.php?f=32&t=596

    viewtopic.php?f=32&t=33

    viewtopic.php?f=32&t=6706&p=21505&hilit=noid#p21505

    viewtopic.php?f=55&t=3108&p=8292&hilit=noid#p8292

    viewtopic.php?f=32&t=168

    viewtopic.php?f=32&t=2697&p=7173&hilit=noid#p7173
     
    Last edited by a moderator: Sep 23, 2015
  10. grumpyvette

    grumpyvette Administrator Staff Member

    just a reminder to check the rather obvious, I got a call from a friend that was having a great deal of difficulty starting his 1992 corvette.
    (Thats the first year for the LT1) that corvette, had been in storage for several years,(3-4 he doesn,t remember,) well, he could get the engine to spin,after installing a new battery,and the ignition worked ,his plugs had spark, he could hear the fuel pump run, and the fuel gauge showed he had about 1/4 tank of fuel, but the car would not fire up, I listened to him describe his problem and suggested he drain the old fuel and replace it with a fresh 10 gallons and some fuel system cleaner/injector cleaner and replace the fuel filter and then place a fuel pressure gauge on the injector fuel rail shrader valve and if he was getting good fuel pressure to call me back. well he calls me back and said he replaced the fuel filter and he had fuel pressure on the shrader valve because he took the cap off and depressed the valve and got a few drops of fuel, but he had zero idea as to pressure as he doesn,t have a pressure gauge, and could I please come over and help?
    I agreed but told him to buy 10 gallons of fresh fuel, and two different brands of fuel injection cleaner.
    well I get there and he wants to show me how it won,t start, I hooked up a pressure gauge on the shrader valve and got a 15 psi reading that dropped to zero in under 2 minutes when he turned on the car, I told him to pour in the first five gallon can of fresh fuel and one can of injector cleaner , into the tank, the fuel gauge never changed, but the engine started, but ran like crap, the gauge on the fuel rail shrader valve shower 35 psi bouncing to 40 psi then down to 30 psi and back up etc.
    I told him to shut it down, I checked he was 2-3 quarts low on oil, I had him do an oil and filter change and add the second five gallon can of fresh fuel, then start the engine and let it run for 4-5 minutes while I checked voltages, grounds etc. the result was that his basic issue was he was trying to start the car with 3 year old fuel, the fresh fuel , new fuel filter, oil change, and injector cleaner seemed to cure his problem, as within minute the car was running fairly smoothly,but with the fuel pressure bouncing IM fairly sure the fuel pumps on its way out or the pre filter screen in the tanks fuel pump, is partly, clogged, his main problem was the fact that 3-4 year old fuel was in the car and the gas gauge seems to need repairs, as its not reading correctly and Im reasonably sure the fuel pumps going to need replacing,
    you can,t expect a car to sit with zero maintenance for 3-4 years and have it fire right up without having some issues, I'm sure he will get these worked out .
    and yes before someone brings it up, I also suggested inspecting or replacing the fuel pressure regulator, fuel pump, vacuum lines, spark plugs, air filter, fuel tank pre-screen filter, checking the fuel gauge, fuses, and setting the TPS and IAC and cleaning the injectors.
    I also suggested he check all the sensor resistances and voltage readings, and checking trouble codes and grounds.


    and I showed him these links below which Im sure will eventually become useful

    viewtopic.php?f=32&t=33

    viewtopic.php?f=32&t=3429

    viewtopic.php?f=32&t=2697&p=18904&hilit=sensors#p18904

    viewtopic.php?f=80&t=728&p=9217&hilit=sensor+ohms#p9217

    viewtopic.php?f=32&t=1836

    viewtopic.php?f=32&t=816

    viewtopic.php?f=32&t=304

    viewtopic.php?f=32&t=168

    viewtopic.php?f=36&t=628

    viewtopic.php?f=32&t=1773&p=4506&hilit=corvette+shop+manual#p4506

    viewtopic.php?f=80&t=1470&p=3304&hilit=corvette+shop+manual#p3304

    and yes it may look difficult or intimidating, but its just not that hard to do correctly if you take your time and read up on whats required
     
  11. grumpyvette

    grumpyvette Administrator Staff Member

    [​IMG]
    [​IMG]

    IF YOU FAIL TO LOOK THRU THE SUB LINKED INFO YOULL MISS A TON OF GOOD INFORMATION
    http://www.chevythunder.com/fuel%20inje ... pg%20B.htm
    a defective or loose connector on your intake air manifold temp sensor can cause starting issues,that sensors located on the under side of the plenum about the center-line of the rear of the plenum, near where the green arrow points, its usually easier to reach the connector from the pass side of the plenum/runners, and this sensor works better if moved to the forward air intake, there are wire kits to do the relocation
    [​IMG]
    [​IMG]
    viewtopic.php?f=70&t=7309&p=24868#p24868

    http://chevythunder.com/fuel%20injectio ... pg%20C.htm

    viewtopic.php?f=44&t=366&p=448#p448

    Corvette Intake Air Temperature Sensor Relocating Kit, L98,1985-1991
    http://www.austinthirdgen.org/index.php?pid=24

    READ THIS
    http://tpiparts.net/85_89_maf_sensors/
    The Air Temperature Relocating Kit repositions your engine's air intake temperature sensor from the hot plenum area to the air filter base where it can sense cooler air. This enables the ECM to adjust the fuel to more accurate air temperatures resulting in increased engine performance. This kit can be used with or without the forced air induction system. The kit includes: IAT sensor, CAD/CAM designed & CNC machined aluminum mount bracket with stainless steel hardware, 78" extension harness, cable ties & installation instructions. Fits all 1985-91's except ZR1 models.

    http://www.ecklerscorvette.com/1985+che ... -1991.html
    1985 Chevy Corvette Standard Intake Plenum Manifold Air Temperature Sensor
    [​IMG]
    Replacement Sensor
    Gray Wire Connector End
    Open Probe

    This Corvette replacement intake plenum manifold air temperature sensor has been manufactured to meet or exceed factory specifications and performance. You will find the fit and function will work perfectly for your Corvette. You will also be pleased to know that Eckler's has sourced this intake plenum manifold air temperature sensor among other possible parts as the best choice for your repair or restoration project.




    By: BigBabyLou

    Why

    The main reason is so that the ECM sees the correct air temperature. Three causes why it doesn't:
    1) the Intake Air Temperature (or Manifold Air Temperature) sensor is located in the intake plenum, on its underside, so it is heatsoaked from all the hot surrounding metal.
    2) the stock Intake Air Temperature sensor is nothing but a CTS (Coolant Temperature Sensor) which is a big metal piece with threads and a connector. So in fact, this big piece of metal has NO WAY of measuring the temperature of the air at the big honking metal tip, instead it measures the temperature of the hot manifold.
    3) the intake manifold is full of what? Air? Well, only at WOT. Otherwise (most of the time), there is a lot of vaccum in the manifold (i.e. lack of air). So WHAT air temperature can the sensor measure anyway?


    What

    This picture shows the stock TPI IAT sensor (on the left) vs the V6 IAT sensor (on the right).
    The stock TPI IAT sensor is the same as the CTS sensor and thus measures reliably the temperature of whatever mass it is screwed into. Like the hot intake plenum.
    Whereas the V6 IAT sensor has a protruding plastic sleeve with screens and a sensor pellet placed in the screened openings, to measure the temperature of the airflow through the screens.
    There is no electrical difference in these two sensors whatsoever, their readings are identical, they are completely interchangeable when it comes to their electrical specs and plumbing.
    Oh, I forgot a minor detail: their plugs differ very slightly. But if you shave two tabs on the sides of the connector (with a knife or a file), it will plug in with no problems.

    Where

    The stock TPI IAT sensor is located on the bottom of the upper intake plenum, towards the back. It is facing the lower intake manifold.
    My car came with the filter intake runners that supposedly go on a V6 engine and that have a 3/8" NPT hole in the side. Specifically for the IAT. So this is the place where I installed the new IAT.

    How

    The stock TPI IAT sensor is in a not very accessible location. It is hard to reach but You might be able to pull the plug off with a thin long screwdriver and some needlenose pliers. Otherwise, take off the upper intake plenum to access the IAT and connector.
    Trace the wireloom behind the passenger valve cover and disconnect it from the black two-prong connector (C121). Splice into the harness and extend it so that it can reach to the new sensor location.
    Purchase (or obtain through other means available to you) an IAT sensor for a V6 MPFI engine and make sure it's the right one.
    (you can also use the IAT sensor from a TBI engine, it has same electrical characteristics and connector)
    (when locating the sensor, be aware that it might be called ACT - Air Charge Temperature, which is more of a Ford term but some stores use it for the Chevy sensor anyway)
    Shave the two tabs on the sides of the IAT connector (with a knife or a file) and make sure that it will plug into the new IAT sensor.
    Install the IAT sensor into its new location (in the air filter runners or elsewhere).
    Now just run the extended wire safely so that it doesn't get caught on any moving parts.
    Disconnect the battery for several minutes so that the computer can relearn how to adjust the mixture with this new reading.

    Picture of the new IAT sensor installed in the air filter runners.
    [​IMG]
    Results

    Many people are VERY skeptical about this change and say that it does not make much of a difference.
    However, from my practical experiment using datalogging software, I can say without exaggeration that I've seen a 35-degree (F) CONSTANT difference in the intake air temperature measurements.
    With the stock TPI IAT (heatsoaked CTS part), the computer saw 132 degrees in the intake on a 95 degree night. That measurement was performed on the highway, i.e. with lots of air flowing through the engine compartment. Stopped at idle, the temperature reading was even higher.
    With the relocated TBI IAT sensor, the computer saw 97 degrees on the SAME night, with 95 degrees outside. Again, this measurement was performed on the highway but the reading did not increase much at lower speeds or at idle.

    So there, it's not a myth and if done properly, the computer will see the REAL air temperature. And especially in Texas, that makes a world of difference.



    85-89 MAF TPI Systems

    Below is a list of all the needed sensors to install a MAF TPI setup, and each of their functions.

    Mass Air Flow (MAF) Sensor: This sensor is responsible for measuring air volume and density. It is located in the air duct, before the throttle body. All of the air that the engine consumes must first pass through the MAF sensor. At the center of the MAF, is a very thin wire whose resistance increases as it goes up in temperature. A constant voltage is applied to this wire. Air being drawn through the MAF has the effect of cooling this wire, which lowers its resistance, and increases current. As you might suspect, the more air is drawn through the MAF sensor, the greater the current flow. It is important to note that hot dry air is less dense and has less mass than cool moist air. As a result, hot dry air will cool the wire less than cool moist air.

    A circuit mounted on the MAF sensor serves to convert the current flow into a variable frequency square wave on 1985 models, which is sent to the ecm. MAF units from 86-89 models output a simple analog signal instead of using frequency modulation like the 1985 units. The ecm will calculate the amount of fuel needed depending on the signal from the MAF sensor. It is very important that there are no air leaks (from a ripped air duct for example) between the MAF and the throttle body.
    Oxygen Sensor: Responsible for determining the amount of oxygen in the exhaust manifold. Depending on how much oxygen is in the exhaust, the ecm can determine whether or not the air/fuel mixture is rich or lean. The signal sent to the ecm by the ecm varies between 0.0 and 1.0 volts. An ideal mixture (also known as a Stoichiometric mixture) of 14.7:1 is represented by .450 volts. If the oxygen sensor voltage is below .450, then the air/fuel mixture is lean. Anything over .450 means the mixture is rich. Since the sensor is essentially just a switching device, it will be fluctuating alot between lean and rich. This is normal, and an indication that the sensor is in working properly.

    Keep in mind however that oxygen sensors (except wideband oxygen sensors), are not very accurate below or above .450 volts. Exhaust gas temperature will affect the oxygen sensor reading as well. The sensor will not read properly until exhaust gas temperature reaches approximately 600 degrees Farenheit. If you have headers installed, it is a good idea to use a heated oxygen sensor (3 wire) instead of the usual single wire sensor. Headers usually place the oxygen sensor further down the exhaust stream, where exhaust temperatures are cooler. A heated oxygen sensor will heat itself, allowing a more reliable sensor reading than a single wire sensor. If you have factory exhaust manifolds, then the single wire sensor is adequate.

    Oxygen sensors are a regular maintenance item, and should be replaced every 30,000 miles. When an oxygen sensor goes bad, it tends to read lean, and will not fluctuate very much. The ecm will attempt to correct this false lean condition by richening the mixture. This will cause poor driveability, and high gas consumption.
    Knock Sensor: Also known as detonation sensor, it is responsible for sensing spark knock. Basically, thats when the fuel mixture ignites before the spark plug fires. The piston is moving upwards as this premature combustion takes place. Since fuel is used to cool down the combustion chamber, a lean condition causes the temperature to rise, and ignites the fuel mixture prematurely. This is very abusive on the engine internals, and reduces the life of any engine. The more powerful the engine, the greater the potential for damage. Detonation can be cause by a variety of things. One of the more common causes on TPI retrofits where prom changes have been made to the fuel or spark tables is a lean condition. It isn't always loud enough to be heard, so just because you don't hear any pinging, doesn't mean its not happening.
    [​IMG]
    Detonation will cause a vibration to travel through the engine block. The sensor listens for this vibration at a certain frequency, and sends a signal to the ecm when the frequency is heard. This frequency is different depending on engine size. To prevent possible engine damage, the spark timing needs to be retarded when detonation is present. The sensor itself does not pull the timing back however. The ecm is in charge of retarding the timing, and will do so according to a series of settings inside the prom. The knock sensor is located on the passenger side of the engine block on factory applications. It can however be relocated to the driver side of the block if needed (header clearance for example). They are different depending not only on the size of the engine, but also the ecm being used. It is important that the correct sensor is used to avoid problems. Although it is possible to run the car without one, I strongly suggest against this. I have had customers come to me looking for a $45 knock sensor after spending several hundred dollars and an extra month of work rebuilding a blown engine due to detonation.
    Throttle Position Sensor (TPS): Responsible for reporting to the ecm the position of the throttle blades. The ecm will receive a signal which can vary from 0.0 to 5.0 volts. At idle, the TPS should be read .54 volts (factory specification) unless it has been set to a different value inside the prom. If it does not read .54 volts and the idle TPS voltage setting has not been modified in the prom, then it should be adjusted. Under full throttle, it should output close to 5.0 volts. Throughout its range of motion, the voltage should climb steadily, without any jumps or falls. If it is not steady or has some fluctuations as it is moved through its range of motion, it should be replaced. This sensor is located on the passenger side of the throttle body.

    Coolant Temperature Sensor (CTS): This is basically a thermistor (means that it changes resistance with temperature) that supplies the ecm with the temperature of the engine coolant. This temperature reading is used for several important functions. The most notable is that the ecm adds extra fuel to an engine when its cold, and as the engine warms up, the extra fuel is reduced. This sensor mounts at the front of the intake manifold. The chart below shows the approximate resistance for this sensor in relation to temperature.
    Intake Air Temperature Sensor (IAT): This sensor is also a thermistor (means that it changes resistance with temperature) that supplies the ecm with a temperature reading of the air being drawn into the engine. It is the same as the coolant temperature sensor on 86-92 models. The 1985 intake air temperature sensor used a different connector and cannot be used as a coolant temperature sensor because it had an exposed bulb. This sensor mounts underneath the plenum. The chart above shows the approximate resistance for this sensor in relation to temperature.

    Idle Air Control (IAC) Valve: Although this is technically not a sensor at all, people often treat it as one. It is responsible for regulating the amount of airflow being admitted into the engine to adjust engine speed, particularly at idle and deceleration. The ecm controls the IAC at its discretion. The IAC works by moving a cone shaped pintle, which can extend and retract as needed to admit or block off incoming air. The valve moves the pintle in "steps". These steps are numbered and range from 0 to 160. A properly adjust throttle body should be idling when warm between 15-25 steps.

    The IAC is used under a variety of conditions, not only at idle speed. The valve mounts on the bottom coolant plate of the throttle body.

    Vehicle Speed Sensor (VSS): This is responsible for providing the ECM with the vehicle speed. It can be located either at the tailshaft of the transmission, or behind the speedometer on cars with a cable driven speedometer. It sends a 2k ppm (pulse per mile) square wave signal, and is needed for a variety of functions. It is absolutely critical for the ecm's learn mode, timing retard, emissions, torque converter lockup (automatic lockup transmissions only), idle speed control, and to avoid stalling on deceleration. It is possible to run without one. However, your car will NOT be street legal if you are required to retain emissions equipment, the ecm will not control the torque converter lockup, the ecm will not retard timing if you run into detonation, and it is possible to run into stalling /idle speed issues. In addition, the ecm will not adjust the fuel table properly as you drive (known as its "learning ability"). If the ecm does not know the vehicle speed it is assumed to be 0 mph.

    If you still insist on not running a vss, I very highly suggest that the minimum vehicle speed for timing retard be brought down to 0 mph in the prom. The factory setting is 2 or 3 mph. If you don't bring this value down, and you do not run a vss, the ecm will NOT retard your timing under detonation.
     
    Last edited by a moderator: Nov 27, 2015
  12. grumpyvette

    grumpyvette Administrator Staff Member


    yes it will take you some time but it will be worth the effort to read thru the links and sub linked info below look I know its going to take some research, and testing, Im well aware is frustrating,
    but randomly replacing components is a rather expensive and far from effective way to fix the issue
    and while reading links <AND SUB LINKS) might be painful , but it will lead you to the source of the problem
    you need to get a shop manual, and multi meter and start checking each stage of the process


    viewtopic.php?f=32&t=1401

    viewtopic.php?f=80&t=728&p=1025&hilit=sensors+camaro#p1025

    http://www.hotrod.com/articles/innovate-air-fuel-ratio-meter/

    viewtopic.php?f=32&t=2697

    viewtopic.php?f=70&t=1015

    viewtopic.php?f=70&t=875

    viewtopic.php?f=70&t=294

    viewtopic.php?f=70&t=2798

    viewtopic.php?f=70&t=1701

    viewtopic.php?f=70&t=3301

    viewtopic.php?f=70&t=251

    viewtopic.php?f=70&t=4683

    If you look over the threads on this and most other sites related to cars you'll see a recurring theme,and that theme is related to the total frustration many guys seem to feel when the car engine won,t run or run correctly, and for some reason the average response is to start throwing random guess work list of new parts at the problem, rather than stepping back, and doing a logical list of tests and braking out the shop manual, multi meter, vacuum and fuel pressure gauges and a timing light and using the tools too isolate the source of the problem by testing sensors,electrical connections and function of each related component , AFTER RESEARCHING the problem.
    the basics remain the same
    you need compression ],
    which means the rings and valves must seal the cylinder and the cam lobe timing must be CORRECTLY indexed to the crank rotation
    YOU NEED FUEL
    which means the carburetor or injectors on the engine must get an adequate flow and consistent pressure, and must atomize that fuel and mix it with air flow in the proper ratio.
    YOU NEED ignition
    which means the spark plugs must fire, or arc, at the proper time in relation to piston location as the crank and cam rotate,with a spark or adequate heat and duration to ignite the compressed fuel air mix
    YOU NEED AN UN RESTRICTED AIR FLOW ]
    which requires that both the intake manifold and exhaust system allow near unrestricted flow into and out of the engine
    YOUR ENGINE MUST BE PROPERLY LUBRICATED
    which both reduces heat and wear and keeps the engine from seizing up, or getting into detonation or having parts fail from heat stress
    YOU NEED A COOLING SYSTEM
    to maintain the engines operational temperature in its intended range, and reduce wear and parts failure so the lubrication and cooling systems, operate together.
    ALL THE SENSORS MUST WORK, SO CHECK YOUR ELECTRICAL CONNECTIONS, FUSES AND GROUNDS

    if one or more of these functions or the sensors that control these functions fails your engine won,t operate correctly so its your job to isolate the problem


    First thing we will do is check for Fuel, lets do a quick check list

    http://members.shaw.ca/corvette86/FuelS ... gnosis.pdf
    you might be amazed at what a few tests with a fuel pressure gauge can tell you
    [​IMG]
    viewtopic.php?f=70&t=7309&p=24862&hilit=noid#p24862

    Install the fuel pressure gauge onto the shrader valve on the fuel rail. you should get about 40 psi when the keys turned on, and it should hold at 40 psi for several minutes after the keys turned off, if that doesn,t hold a injector or the pressure regulator leaks, or the fuel pumps defective
    [​IMG]

    [​IMG]

    [​IMG]
    https://www.centuryperformance.com/foru ... -Coil-Tech
    [​IMG]

    ONE FACTOR THATS RARELY UNDERSTOOD ,is that you need consistent voltage and current values to keep a consistently effective ignition working as its designed and in many cars the stock alternator is MARGINAL at best at supplying the ignitions needs, Ive seen some rather remarkable improvements in engine performance at times when upgrading the alternator from a stock 110-120 amp OEM type to the 200 amp aftermarket alternators in several muscle cars and corvettes

    http://www.globaldenso.com/en/products/ ... tions.html
    [​IMG]
    [​IMG]
    [​IMG]

    if you find you have fuel, you can now verify ignition spark
    a simple test is to pull a plug wire and insert a #2 phillips screw driver into the plug boot , you then hold the plastic handle so the steel shaft is about 1/4" from a good electrical ground while a friend hits the starter to spin the engine, you should see a spark jump the gap
    READING ALL THE WAY THROUGH these links might be helpful, they cover a wide range of related info


    http://www.thirdgen.org/tpimod2

    http://www.thirdgen.org/injectorswap

    viewtopic.php?f=32&t=33

    viewtopic.php?f=52&t=196

    viewtopic.php?f=32&t=596

    viewtopic.php?f=50&t=6323&p=19860&hilit=aldl#p19860

    viewtopic.php?f=36&t=63&p=31920&hilit=shop+manual#p31920

    viewtopic.php?f=32&t=168

    viewtopic.php?f=32&t=661

    viewtopic.php?f=32&t=5926

    viewtopic.php?f=32&t=302

    viewtopic.php?f=36&t=628&p=15040&hilit=opti#p15040

    viewtopic.php?f=80&t=728&p=9217&hilit=vacuum+diagram#p9217

    viewtopic.php?f=32&t=1773&p=4506#p4506

    viewtopic.php?f=87&t=332&p=14272&hilit=leakdown#p14272.

    a great many electrically conductive surfaces are subject to oxidation and corrosion especially things like battery grounds on frames and the newer screw on the side battery cable connections, and battery to starter connections,so coating those higher amp rated connection points with a good anti corrosive, and moisture resistant and electrically conductive paste , grease or anti-seize would seem to be a good idea.
    I know I can,t be the only guy that used to occasionally find when I hit the ignition key and got a click but the starter would not work, and found that a loose battery connection on the cable was at fault!

    [​IMG]


    http://www.2spi.com/catalog/vac/silver-filled-grease-techdata.html

    http://www.cool-amp.com/conducto_lube.html?gclid=CNKs1MD-sMYCFZKBaQodGswC6A

    http://www.w8ji.com/dielectric_grease_vs_conductive_grease.htm

    http://www.carid.com/loctite/copper...Put_9z-sMYCFQGGaQodOMID_Q#product-details-tab

    [​IMG]
     
    Last edited by a moderator: Nov 13, 2016
  13. grumpyvette

    grumpyvette Administrator Staff Member

    "hey grumpy, when I parked my 1985 TPI corvette a couple weeks ago it was running fine, I went to start it, the fuel pump runs while the engines cranking,but it acts like theres no gas getting sprayed from the injectors, the engine spins, I have ignition spark at the plugs, and I can hear the fuel pump run constantly, but the engine won,t fire up, any ideas?"









    just because the fuel pump runs doesn,t guarantee you have fuel pressure at the fuel rails , so the obvious first test is to pour a couple gallons of fresh fuel into the fuel tank and verify theres pressure at the fuel rail shrader valve on the rear of the pass side fuel rail.the fuel pump should only run long enough to build to about 38psi-42psi then shut off and start intermittently if the fuel pressure is reduced, while the engine spins AS LONG AS YOU HAVE 5 psi of oil pressure the fact that the fuel pump continues to run while your cranking the engine seems to indicate you have the required oil pressure so the fuel pumps getting voltage.
    so many guys don,t bother,to post both the problems they see and the solutions they eventually find, and that makes it much harder on those looking for answers to similar issues.
    and yes defective injectors,bad electrical connections, defective sensors, or fuel system supply issues and vacuum leaks are frequently the cause of " ENGINE SURGING", or "MISSING" yet most guys want to instantly start swapping parts rather than testing to isolate the cause.
    some time spent with a shop manual and multi meter , and fuel pressure gauge and knowing a list of sensor voltage/resistance readings, and reading the shop manual, and basic research like checking your fuses are ok and the alternator and battery function correctly and looking for loose grounds, can do a great deal toward isolating a problems source.
    [​IMG]

    Id first test the injector fuses theres two in a 1985 vette, the injectors will not squirt enough fuel to start the engine in most cases if one of the injector fuses is blown
    [​IMG]
    [​IMG]

    if you have at lease 38 psi in the fuel rail, and it holds at or near at least 38 psi for at least a couple minutes after you stop cranking the engine, the fuel pressure regulator is most likely functioning correctly, but you state the injectors are not squirting fuel and the pump keeps running while you crank the engine?
    you can test the electrical connectors on the injectors with a noid test light to watch the electric pulse,at each injector location, ID verify timing injector resistance,and check for vacuum leaks while testing, and remember theres a 9th cold start injector on the 1985-88 TPI fuel rail.
    remember the fuel pump supply's fuel flow from the tank toi the injector fuel rails, but its the controlled resistance to fuel flow in the fuel pressure regulator that produces the fuel PRESSURE ,you read with the gauge at the shrader valve on the fuel rail, if the fuel pressure diaphragm is ruptured it results in little or no fuel pressure even if the fuel pump works because fuel is just being pumped from the tank thru the fuel rails and back to the tank via the fuel return lines with very little resistance to build pressure.

    THIS RETURN STYLES FAR MORE CONSISTENT

    because fuel flows strait thru at all times but as soon as resistance to flow exceeds the set pressure level the adjustable spring seat is seat at, the relief valve to the return line is forced open and all excess pressure and flow exits into the return line maintaining the set pressure but preventing any further increase, but never interrupting fuel flow
    [​IMG]
    a very common problem on older TPI systems is a leaking fuel pressure regulator diaphragm, leak, or rupture, resulting in excessive fuel in the plenum,as it gets sucked past the defective diaphragm , up into the plenum thru the vacuum line, and a very low fuel pressure reading at the shrader valve on the fuel rail, the most likely source of that problem, is a ruptured or leaking fuel pressure regulator diaphragm thats allowing fuel to flow up the vacuum hose into the plenum, as its very unlikely all 8 injectors are leaking, that would account for the fuel pressure drop and all 8 cylinders showing excess fuel contamination
    [​IMG]
    replacement diaphragm
    RETURN STYLE FUEL PRESSURE REGULATOR
    2 fuel pressure diaphragm
    3 fuel flow chamber and pressure route chamber
    4 boost reference connection
    5 pressure adjustment
    8 return line valve and exit
    viewtopic.php?f=55&t=635

    IF you can,t locate a 9th injector and yours is defective on an early TPI,you can use an injector delete ,block off kit, it will take a bit longer to fire up on a few cars but generally its not required and upgrading the computer can eliminate its need all together
    [​IMG]
    [​IMG]
    Chevy TPI SBC Cold Start 9th Injector Block Off Delete Kits ARE AVAILABLE
    [​IMG]
    read these threads and sub links, full of related info

    viewtopic.php?f=70&t=7309&p=24862&hilit=noid+test+light#p24862

    viewtopic.php?f=55&t=606&p=7969&hilit=noid#p7969

    viewtopic.php?f=70&t=875&p=31963&hilit=multi+meter#p31963

    http://members.shaw.ca/corvette86/Engin ... ontRun.pdf

    http://members.shaw.ca/corvette86/FuelS ... gnosis.pdf

    viewtopic.php?f=32&t=33&p=41&hilit=9th+injector#p41

    viewtopic.php?f=36&t=63&p=76&hilit=9th+injector#p76
     
    Last edited: May 12, 2015
  14. grumpyvette

    grumpyvette Administrator Staff Member

    Its become obvious from the questions I get that some guys reading the thread don,t seem to have the basic concepts on either how to test or what to look for while they test and what the results of testing tells you so ill try to break it down into the basics.

    FIRST , youll want a few basic tools so Is suggest you get a SHOP MANUAL FOR YOUR YEAR CAR,a SCAN TOOL WILL BE USEFUL and ill post links as usual.
    A MULTI METER, and yes at times it helps to have both an analog and digital multi meter so if you can get both,
    also a TIMING LIGHT,AND a NOID LIGHT KIT,
    a fuel pressure gauge , and both an analog and digital
    you really need to purchase a multi meter and a SHOP MANUAL and look thru the schematics
    without testing there's almost no way to locate the source of your problem,, testing will tell you
    ID strongly suggest you look over the links and locate the fuse panel on the pass side of the dash under the panel cover with the door open on that side and the larger fuses in two separate rectangular black plastic covered holder near the rear drivers side fire wall near the battery, and use the multi meter to verify ALL the fuses test good! with a PROBE each side of the fuse should read the same, if one side shows voltage and the other shows none the fuse may be blown.

    http://www.helminc.com/helm

    [​IMG]
    [​IMG]
    http://www.harborfreight.com/5-in-1-dig ... 98674.html
    LOTS OF RELATED INFO IN THESE LINKs
    viewtopic.php?f=50&t=9478&p=34812&hilit=noid#p34812

    viewtopic.php?f=80&t=728&p=9217&hilit=sensors+camaro#p9217

    viewtopic.php?f=70&t=7309&p=24862&hilit=meter+manual+gauge#p24862

    http://www.mainstreamtopics.com/forums/ ... iagnostic/

    viewtopic.php?f=55&t=606&p=7969&hilit=noid#p7969

    OK, theres SIX main areas to concern yourself with, that youll want to be testing and isolating the problem too!
    (1)COMPRESSION OR MECHANICAL ISSUES
    (2) FUEL DELIVERY AND PRESSURE
    (3)IGNITION RELATED
    (4) SENSOR RELATED
    (5) CPU control
    (6) ELECTRICAL CONNECTIONS



    (1)COMPRESSION OR MECHANICAL ISSUES
    youll need to verify all your cylinders have near equal compression, a simple compression test will help, all cylinders should read within 10% of each other , if any read less than about 90psi you more than likely have worn rings detonation damage or badly adjusted valves or a leaking valve so obviously those conditions will need to be checked, readings below 70 psi usually indicate mechanical or detonation damage
    viewtopic.php?f=87&t=332&p=14272&hilit=leakdown#p14272

    viewtopic.php?f=52&t=196

    (2) FUEL DELIVERY AND PRESSURE
    First thing we will do is check for Fuel, lets do a quick check list
    on a properly operating TPI system you should see near 40-43 PSI on the fuel rail, when you try to start the car, if the fuel pressure falls rapidly when you turn off the key check the vacuum line on the fuel pressure regulator for raw fuel, if you see raw fuel its usually indicating a leaking fuel pressure regulator diaphragm, that needs to be replaced, if you see pressure drop slowly you might have a defective leaking injector dribbling fuel into a cylinder, check all the spark plugs none should be wet / black or fuel fouled.
    you could also have a defective fuel pump.

    READ THESE LINKS SEVERAL TIMES CAREFULLY

    viewtopic.php?f=32&t=33

    viewtopic.php?f=32&t=596

    http://members.shaw.ca/corvette86/FuelS ... gnosis.pdf



    http://www.corvettebuyers.com/c4vettes/l98.htm

    http://garage.grumpysperformance.co...roblem-getting-the-engine-started.63/#post-76

    you might be amazed at what a few tests with a fuel pressure gauge can tell you, and you should hear the fuel pump run for about 3 seconds to pressurize the fuel rails when you first turn the key.
    your SHOP MANUAL HAS A FUEL PUMP TEST AND FUEL PUMP RELAY TEST PROCEDURE LISTED

    with the key on but engine off you should see 12 volts on the orange or pink wire on the fuel pump relay, the black wire goes to frame ground. if you have voltage and the fuel pump runs , fine, if not with the key on and engine off and after verifying all fuses are good check the dark green and white on the fuel pump relay while cranking the car this is the pmc lead that triggers the relay, if its hot the pmc is most likely ok, if not check the wire for corrosion , or breaks in the wire , if its dead the pmc might be defective, if all the leads check replace the relay if it fails to provide voltage to the fuel pump.
    get out your shop manual, look at the diagram carefully, your SHOP MANUAL HAS A FUEL PUMP TEST AND FUEL PUMP RELAY TEST PROCEDURE LISTED and shows you how to bye-pass the fuel pump relay with a jumper
    [​IMG]

    viewtopic.php?f=70&t=7309&p=24862&hilit=noid#p24862

    viewtopic.php?f=32&t=67

    viewtopic.php?f=32&t=2697&p=29270&hilit=+sensors+location#p29270

    viewtopic.php?f=80&t=728&p=9217&hilit=+sensors+location#p9217

    viewtopic.php?f=70&t=9206&p=33081&hilit=+sensors+location#p33081

    Install the fuel pressure gauge onto the shrader valve on the fuel rail. you should get about 40 psi when the keys turned on, and it should hold at 40 psi for several minutes after the keys turned off, if that doesn,t hold a injector or the pressure regulator leaks, or the fuel pumps defective
    [​IMG]

    [​IMG]
    [​IMG]
    http://garage.grumpysperformance.co...urrent-flow-grounds-and-more.3504/#post-54625

    http://garage.grumpysperformance.co...hooting-tip-for-electronics.11317/#post-51557

    [​IMG]
    if you find you have fuel, you can now verify ignition spark
    a simple test is to pull a plug wire and insert a #2 phillips screw driver into the plug boot , you then hold the plastic handle so the steel shaft is about 1/4" from a good electrical ground while a friend hits the starter to spin the engine, you should see a spark jump the gap
    READING ALL THE WAY THROUGH these links might be helpful, they cover a wide range of related info


    http://www.thirdgen.org/tpimod2

    http://www.thirdgen.org/injectorswap

    viewtopic.php?f=32&t=33

    viewtopic.php?f=52&t=196

    viewtopic.php?f=32&t=596

    viewtopic.php?f=50&t=6323&p=19860&hilit=aldl#p19860

    viewtopic.php?f=36&t=63&p=31920&hilit=shop+manual#p31920

    viewtopic.php?f=32&t=168

    viewtopic.php?f=32&t=661

    viewtopic.php?f=32&t=5926

    viewtopic.php?f=32&t=302

    viewtopic.php?f=36&t=628&p=15040&hilit=opti#p15040

    viewtopic.php?f=80&t=728&p=9217&hilit=vacuum+diagram#p9217

    viewtopic.php?f=32&t=1773&p=4506#p4506
    [​IMG]


    (3)IGNITION RELATED

    verify the optical sensor in the opti-spark ignition is correctly functioning, disconnect a single injector plug and plug in the noid light crank the cars engine the noid light should flash as the injector pulse signal voltage cycles, if you don,t have a noid light use a ANALOG MULTI METER , connected to the pink injector connector wire with the other analog meter lead to frame ground,as the bouncing indicator needle makes the voltage pulse obvious.
    [​IMG]
    [​IMG]

    [​IMG]
    he next step is to use a multi meter and verify injector resistance, it should be consistent within an OHM or two between all injectors depending on brand most c4 corvette injectors will read 12-15 OHMS resistance.
    Id then check the fuses and use a NOID test kit
    viewtopic.php?f=55&t=606&p=7969&hilit=noid#p7969
    [​IMG]
    viewtopic.php?f=36&t=628&p=39398&hilit=opti#p39398

    viewtopic.php?f=70&t=2798

    viewtopic.php?f=70&t=4683

    viewtopic.php?f=70&t=202

    viewtopic.php?f=70&t=962
    (4) SENSOR RELATED

    viewtopic.php?f=50&t=9478&p=34812&hilit=camaro+sensor#p34812

    http://www.corvettebuyers.com/c4vettes/l98.htm

    viewtopic.php?f=80&t=728&p=25843&hilit=camaro+sensor#p25843

    Start the engine. It may take a few seconds for the car to catch on to its new settings.

    this infos bound to be helpful at times
    Sensor Locations

    Sensor
    Location

    Engine Coolant Temperature Sensor. Front of engine, below Throttle Body.
    Engine Oil Temperature Sensor. Left rear of engine, just above the oil filter.
    Oil Pressure Sender/Switch. Top, left hand rear of engine.
    Fuel Quantity Sender. Top of fuel tank, beneath filler pipe escutcheon panel.
    MAT (Manifold Absolute Temperature Sensor). Underside of manifold air plenum at rear.
    Outside Temperature Sensor. Right side of engine, top right corner of radiator.
    In Car Temp Temperature Sensor. Coupe: above left seat near interior courtesy light, Convertible: center of cargo compartment lid.
    MAF (Mass Air Flow) Sensor. Front of engine ahead of throttle body.
    Oxygen (O2) Sensor. Left side of engine, in exhaust pipe.
    TPS (Throttle Position Sensor). Right side of throttle body at the front.


    Sensor Outputs:

    Sensor
    Measured Value

    Engine Coolant Temperature Sensor. 185 Ohms @ 210F, 3400 Ohms @ 68F, 7,500 Ohms @ 39 F.
    Engine Oil Temperature Sensor. 185 Ohms @ 210 F, 3400 Ohms @ 68 F, 7,500 Ohms @39 F.
    Oil Pressure Sender/Switch. 1 Ohms @ 0 PSI, 43 Ohms @ 30 PSI, 86 Ohms @ 60 PSI.
    Fuel Quantity Sender. 0 Ohms @ Empty, 45 Ohms @ 1/2 Full, 90 Ohms @ Full.
    MAT (Manifold Absolute Temperature Sensor). 185 Ohms @ 210 F, 3400 Ohms @ 70 F, 15,000 Ohms @ 40 F.
    Outside Temperature Sensor. 4400 Ohms @ 60 F, 2200 Ohms @ 85 F.
    In Car Temp Temperature Sensor. 4400 Ohms @ 60 F, 2200 Ohms @ 85 F.
    MAF (Mass Air Flow) Sensor. .4 Volts @ idle, 5 Volts @ Full Throttle.
    Oxygen (O2) Sensor. .1 Volt Lean Mixture, .9 Volt Rich Mixture.
    TPS (Throttle Position Sensor). .54 Volts Idle, ~ 5 Volts Full Throttle.
    grumpyvette is online now Report Post IP Edit/Delete Message



    RELATED INFO LINKS
    viewtopic.php?f=70&t=4309&p=11361&hilit=multi+metter#p11361

    viewtopic.php?f=44&t=469&p=9093&hilit=scanner#p9093

    viewtopic.php?f=36&t=3105&p=8272&hilit=+connectors#p8272

    http://www.gmhightechperformance.com/te ... modifying/

    HERES A FEW USEFUL, related bit of info and LINKS YOU MIGHT WANT TO LOOK THRU
    http://www.diy-efi.org/gmecm/papers/tunetip.html

    http://www.diy-efi.org/gmecm/papers/prog_101.html

    http://www.eecis.udel.edu/~davis/z28/

    http://para.noid.org/~lj/PCM Tutorial/PCMtutorial.htm

    http://www.diy-efi.org/gmecm/faq/tbi_fp.html

    http://www.diy-efi.org/gmecm/faq/gm_connectors.html

    http://www.diy-efi.org/gmecm/
     
    Last edited by a moderator: Oct 13, 2017
  15. grumpyvette

    grumpyvette Administrator Staff Member

    90-92 Speed Density TPI Systems

    Below is a list of all the needed sensors to install a speed density TPI setup, and each of their functions.

    Manifold Absolute Pressure (MAP) Sensor: This sensor is responsible for measuring manifold air pressure. In simple terms, it measures engine vacuum inside the intake manifold. The lower the vacuum reading, the greater the load on the engine (i.e. heavy acceleration). The higher the vacuum reading, the lower the load on the engine (i.e. cruising or light throttle). The ecm needs this information to calculate how much fuel the engine needs. An engine under heavy load will require more fuel than an engine under light load. The MAP sensor is usually located on a bracket on the passenger side of the plenum. It may however be mounted on the firewall, or somewhere close by.

    The ecm will see a signal from the MAP sensor which will vary from 0.0 to 5.0 volts. Under full throttle (0" of vacuum), it should read close to 5.0 volts. The voltage should drop depending on engine vacuum as described by the chart below:


    [​IMG]


    Oxygen Sensor: Responsible for determining the amount of oxygen in the exhaust manifold. Depending on how much oxygen is in the exhaust, the ecm can determine whether or not the air/fuel mixture is rich or lean. The signal sent to the ecm by the ecm varies between 0.0 and 1.0 volts. An ideal mixture (also known as a Stoichiometric mixture) of 14.7:1 is represented by .450 volts. If the oxygen sensor voltage is below .450, then the air/fuel mixture is lean. Anything over .450 means the mixture is rich. Since the sensor is essentially just a switching device, it will be fluctuating alot between lean and rich. This is normal, and an indication that the sensor is in working properly.

    Keep in mind however that oxygen sensors (except wideband oxygen sensors), are not very accurate below or above .450 volts. Exhaust gas temperature will affect the oxygen sensor reading as well. The sensor will not read properly until exhaust gas temperature reaches approximately 600 degrees Farenheit. If you have headers installed, it is a good idea to use a heated oxygen sensor (3 wire) instead of the usual single wire sensor. Headers usually place the oxygen sensor further down the exhaust stream, where exhaust temperatures are cooler. A heated oxygen sensor will heat itself, allowing a more reliable sensor reading than a single wire sensor. If you have factory exhaust manifolds, then the single wire sensor is adequate.

    Oxygen sensors are a regular maintenance item, and should be replaced every 30,000 miles. When an oxygen sensor goes bad, it tends to read lean, and will not fluctuate very much. The ecm will attempt to correct this false lean condition by richening the mixture. This will cause poor driveability, and high gas consumption.

    Knock Sensor: Also known as detonation sensor, it is responsible for sensing spark knock. Basically, thats when the fuel mixture ignites before the spark plug fires. The piston is moving upwards as this premature combustion takes place. Since fuel is used to cool down the combustion chamber, a lean condition causes the temperature to rise, and ignites the fuel mixture prematurely. This is very abusive on the engine internals, and reduces the life of any engine. The more powerful the engine, the greater the potential for damage. Detonation can be cause by a variety of things. One of the more common causes on TPI retrofits where prom changes have been made to the fuel or spark tables is a lean condition. It isn't always loud enough to be heard, so just because you don't hear any pinging, doesn't mean its not happening.

    Detonation will cause a vibration to travel through the engine block. The sensor listens for this vibration at a certain frequency, and sends a signal to the ecm when the frequency is heard. This frequency is different depending on engine size. To prevent possible engine damage, the spark timing needs to be retarded when detonation is present. The sensor itself does not pull the timing back however. The ecm is in charge of retarding the timing, and will do so according to a series of settings inside the prom. The knock sensor is located on the passenger side of the engine block on factory applications. It can however be relocated to the driver side of the block if needed (header clearance for example). They are different depending not only on the size of the engine, but also the ecm being used. It is important that the correct sensor is used to avoid problems. Although it is possible to run the car without one, I strongly suggest against this. I have had customers come to me looking for a $45 knock sensor after spending several hundred dollars and an extra month of work rebuilding a blown engine due to detonation.
    Throttle Position Sensor (TPS): Responsible for reporting to the ecm the position of the throttle blades. The ecm will receive a signal which can vary from 0.0 to 5.0 volts. At idle, the TPS should be read .54 volts (factory specification) unless it has been set to a different value inside the prom. If it does not read .54 volts and the idle TPS voltage setting has not been modified in the prom, then it should be adjusted. Under full throttle, it should output close to 5.0 volts. Throughout its range of motion, the voltage should climb steadily, without any jumps or falls. If it is not steady or has some fluctuations as it is moved through its range of motion, it should be replaced. This sensor is located on the passenger side of the throttle body.

    Coolant Temperature Sensor (CTS): This is basically a thermistor (means that it changes resistance with temperature) that supplies the ecm with the temperature of the engine coolant. This temperature reading is used for several important functions. The most notable is that the ecm adds extra fuel to an engine when its cold, and as the engine warms up, the extra fuel is reduced. This sensor mounts at the front of the intake manifold. The chart below shows the approximate resistance for this sensor in relation to temperature.

    [​IMG]

    Intake Air Temperature Sensor (IAT): This sensor is also a thermistor (means that it changes resistance with temperature) that supplies the ecm with a temperature reading of the air being drawn into the engine. It is the same as the coolant temperature sensor on 86-92 models. The 1985 intake air temperature sensor used a different connector and cannot be used as a coolant temperature sensor because it had an exposed bulb. This sensor mounts underneath the plenum. The chart above shows the approximate resistance for this sensor in relation to temperature.

    Idle Air Control (IAC) Valve: Although this is technically not a sensor at all, people often treat it as one. It is responsible for regulating the amount of airflow being admitted into the engine to adjust engine speed, particularly at idle and deceleration. The ecm controls the IAC at its discretion. The IAC works by moving a cone shaped pintle, which can extend and retract as needed to admit or block off incoming air. The valve moves the pintle in "steps". These steps are numbered and range from 0 to 160. A properly adjust throttle body should be idling when warm between 15-25 steps.

    The IAC is used under a variety of conditions, not only at idle speed. The valve mounts on the bottom coolant plate of the throttle body.

    Vehicle Speed Sensor (VSS): This is a magnetic speed sensor mounted on the transmission that sends a 4k ppm (pulse per mile) sine wave signal to the ecm. It is responsible for suppling the vehicle speed to the ecm. This is needed for a variety of functions. It is absolutely critical for the ecm's learn mode, timing retard, emissions, torque converter lockup (automatic lockup transmissions only), idle speed control, and to avoid stalling on deceleration. It is possible to run without one. However, your car will NOT be street legal if you are required to retain emissions equipment, the ecm will not control the torque converter lockup, the ecm will not retard timing if you run into detonation, and it is possible to run into stalling /idle speed issues. In addition, the ecm will not adjust the fuel table properly as you drive (known as its "learning ability"). If the ecm does not know the vehicle speed it is assumed to be 0 mph.

    If you still insist on not running a vss, I very highly suggest that the minimum vehicle speed for timing retard be brought down to 0 mph in the prom. The factory setting is 2 or 3 mph. If you don't bring this value down, and you do not run a vss, the ecm will NOT retard your timing under detonation.
     
  16. grumpyvette

    grumpyvette Administrator Staff Member

    IF YOU HAVE AN LT1 vette?
     
  17. Grumpy

    Grumpy The Grumpy Grease Monkey Staff Member

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