stop guessing and deal in proven facts, if your in doubt


The Grumpy Grease Monkey mechanical engineer.
Staff member
On a sbc motor installed and running, there is suspicion that there may be an slightly warmer cam installed. Short of taking The top of this motor apart Is there anyway to confirm through testing of any kind? Like vacuum if there is anything other than an OEM cam installed?

my dad always stated..

"A couple hours , Is well spent in doing carefully documented &,detailed research,
before.... jumping head first off the dock, into any project,.... AS IT can prevent you from wasting month's of non-productive work and a wheel barrow full of cash!!"
yeah, it takes a bit of work and a few accurate tools, but you don,t need to do much compared to tearing the engine totally apart to expose the cam, you can measure lift and duration accurately at a valve retainer or even more accurately with the rockers removed at a push rod tip






a simple dial indicator fixture, on a push rod tip after removing the rockers from the Number 1 cylinder, and a degree wheel on the crank hub,and a piece of graph paper and your time to graph out the lift vs degree of rotation, would give accurate info, that is going to be a whole lot less work and gives you FACTS VS guessing at the answer



all it takes is a tiny bit of research and some math to calculate the ideal rear differential gearing, tires size etc. and transmission gear ratios, and you can certainly select the correct torque converter stall speed if you have a dyno graph of your engines power curve without much difficulty, an hour or so spent in reading and research will provide you with a great deal better performance from most cars.
and a couple days worth of research and doing some math on all of the power trains component parts will provide you with a wealth of info that can prevent you from making costly mistakes.

before you get crazy chasing some problem your be sure it is not an intermittent fuel delivery issue
(1) Do a compression test!
(2) verify your ignition advance curve, and verify the ignition systems working correctly , the spark plugs are new, properly gaped and the ignition wires in excellent condition visually and with an OHMS meter.
(3) adjust your valves, correctly
(4) carefully verify theres no vacuum leaks, in lines or gaskets
(5)Check the fuel delivery system, WITH A GAUGE, while the engines under real operational inertial loads to verify you have a consistent 5-6 psi at the carburetor inlet port
(6) change out the fuel and air filters, especially if over 3-4 months old
(7) actually check your exhaust back-pressure levels
(8) verify your return style fuel pressure regulator and fuel lines function as intended
(10) actually look for and read installation instructions and rated flow and pressure limitations on fuel pumps and filters
(11) If ALL of the above are normal, only then start looking at the carburetor, and tuning issues
putting a load on the engine when warm causes it to stall,
that strongly suggests not all cylinders are firing correctly
I wish you were local, that sounds like a quick and interesting issue to track
you need to drop back and check basics, it almost always , comes down to mis-matched or improperly functioning components or something worm, defective or out of adjustment, the logical isolate and test procedure, and
a few tools like a vacuum gauge,
compression tester,
dial indicator
and stand,
timing light,
and multi meter,
an IR temp gun to detect cylinder too cylinder temp differences,
and a shop manual for your year car,
and/or a few years in the hobby,
doing similar repairs,

will quickly lead you to the source of the problem
battery voltage (generally 12.7 volts with the car not running and 13.9-14.7 with it at idle)
good grounds
(Less than 3 ohms between battery neg pole and frame)
fuel pressure (with a carb, 4.5-6 psi)
fuel volume and delivery (at least a quart ever 30 seconds) at the carb inlet port
verify coil polarity
compression, consistent in all cylinder with-in 10-12 psi, (generally in the 150 psi-190 psi range)
spark delivery at the plugs and less than 100 ohms per foot preferred
firing order,(yeah I know your sure..CHECK IT AGAIN.)

related threads, theres a huge volume of useful info in links and sub-links ignoring those can only hurt your knowledge base.

start by setting the degree wheel on the crank hub at
Top Dead Center for cylinder #1
and personally Id remove the rockers and meassure from the push rod tip and use a piston stop to verify tdc

youll be amazed at the amount of detailed info in threads and sub links Ive put together to help you gentlemen
Last edited:
I recently got a personal e-mail message that was about two pages long detailing the results one of the guys who reads this web-site regularly had, in finding and correcting a problem hes been fighting for about 11 weeks... I shortened it up and paraphrased a few lines but I have to state that the guy brings back so many memories and has had a very similar learning experience, too what many of us older members have had, that I felt posting the basic concept and his response was well worth the time.
most guys have little real experience at isolate and test procedures and many can,t use test equipment or even fully understand what to look for.

you'll find that you'll gain basic skills, own new tools and PAY LESS MONEY ... index.html

you really need
42545.jpg Extech Products

a timing light,
image_3330.jpg ... 95670.html
multi meter,

vacuum gauge,

fuel pressure gauge ... 94190.html

HARBOR FREIGHT, UNDER $40 ... pv309a.asp

SNAP ON $330

SUMMIT $80-$100
compression test /leak down tester


dial indicator with stand


and a degree wheel

damper tool

and a shop manual
and more related reference material
certainly won,t hurt

until you take the time to verify your thoughts your just guessing
checking your ideas and testing is just not that difficult.

GRUMPY, if you want to quote this message it may prove very helpful,
too the other members of your web site,
but Id appreciate it if you left my name out,
of the reference for obvious reasons.
I spent several weeks trying to tune that new engine I installed and I posted half a dozen threads on various web sites asking for tuning help...
well, after wanting to bang my head on a concrete wall and tear my last bits of receding hair line out I was reading through your response's and I thought back to the reference links, you posted weeks ago, (below)
and decided that I may as well start over from scratch as I obviously must have over-looked something!
I thought Id checked everything carefully but I decided to slow down and read carefully and check off each component and do each test and stop assuming that I knew all the answers as it had become all too obvious that I must be over-looking something!
well the truth is I must have read and skipped over the answer a couple dozen times, and it was obviously my fault as I was just too damn lazy to actually verify the basics because I just assumed I could never have made such a simple mistake........but out of frustration I decided to follow each step in the process and I'm ashamed to admit it.... I could have avoided weeks of this frustration.....the end result and the cause of that engine just not running worth a crap!
Id tried looking for vacuum leaks valve adjustments, timing adjustments,I checked fuel pressure, float levels battery voltage and a dozen other reasons to find out why it would not pull hard, what it seemed to run out of power by 4000 rpm.... yes you mentioned it potential cause and yes I ignored it over and over... several times.... I screwed up and the cam was degreed into the engine a full 11 degrees advanced.. my timing marks and the damper did not show true TDC....and I only found that out after I decided to get off my lazy butt, and verify everything like you repeatedly suggested.
the problem could have been a number of things but by dropping back to the basics and like you stated, several times... don,t assume anythings correct until you've verified it... I found the issue, and you know I did not want to pull that timing chain cover and damper because I was 100% sure.... I'd done that correctly....WRONG!
BTW, I had used a cheap timing chain set, so I could save a few bucks... now I see why you constantly refer to CLOYES timing sets, as a good value and I see now that the dot-to-dot cam install is obviously not the way to go if you want to avoid problems!
but most of all skipping , links or assuming makes for a long and frustrating couple of wasted months I wish I had back!
the fact is that due to manufacturing tolerances a dot-to-dot install will frequently be a few degrees off! now most guys might never notice, but it can and frequently does effect the engines power band so getting it correct helps and eliminates one potential source of problems (be damn sure you verify the cams degreed in correctly and the ignition firing orders correct and all the distributor wires go to the correct cylinder,s spark plugs and distributor cap locations)
Last edited:
I recently had a guy ask me to track down the reason his 1985-1991 TPI corvette would not start,
now on the 1996 you can use a code scanner,
because pre-1996 corvettes are not OBDII code scanner compatible you'll need to use the trouble code flasher to get the trouble codes

all the answers are readily available, theres known testing procedures and listed test results you can expect, and procedures listed in the shop manual for isolating and testing components, you don,t need to be a genius, you just need to be logical and persistent and not afraid to learn new things while getting your hands dirty at times, don,t get overwhelmed , break everything down too easy individual problems and tests, verify and test all the sensors,and test for factors like consistent fuel pressure, known temps,expected voltage or ohms resistance, and vacuum readings and don,t randomly start replacing parts as that gets expensive and its rarely the most efficient way to eliminate problems(unless you get really lucky) with modern computer diagnostic software you,ll have some advantages but think logically, most automotive problems still concern, loose electrical connectors, defective sensors, lack of compression, fuel delivery issues ,fuel pressure, vacuum, temperature or electrical issues.

gas as a liquid fuel ,does not burn well, GAS vapor does ignite easily, the hotter the engine is the more rapidly the liquid gas vaporizes thus making starting the engine more easily, the 9th injector is used to richen the F/A mix, to make starting far easier, later engine versions use a software change that lengthens the injector pulse duration to significantly richen the F/A mix its this longer duration in a cold engine that makes starting easier, so you either require the 9th injector or the more updated software that uses the engine temp software to make starting the cold engine easier




a leak down tester is always a good test tool to have access too

If your injectors are leaking, injectors obviously should be under the control of the CPU and should not remain fully open to drip fuel constantly.
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. visually inspect each injector pigtail for loose broken or shorted or grounded connectors or wires
first verify your getting a pulse at each injector and you have 38-42 psi at the fuel rail shrader valve.
its as usual a case of isolate and test , if the injectors are stuck open the injectors defective or its in need of a careful commercial professional cleaning, verify if its the injector or the injector control pulse duration



replacement injector pig tails are available at rock auto for less than $5 each





now theres a logical and methodical ,way to approach a situation like that and it requires a few tools and a bit of common sense and logic.
id start with asking if you hit the starter does the engine spin over?
if not youll need a multi meter to verify your battery is fully charged.

use of a shop manual and multi meter can be very helpful
assuming its spinning the engine but just not firing up?
Id suggest you pull trouble codes and check for a blown fuse, in the pass dash door area and under the hood near the battery fuse bank areas.
check the fuel rails for fuel pressure!

a vacuum and fuel pressure gauge is useful

without testing you simply guessing
never guess, deal in verified FACTS!

guessing is a waste of time
think logically, isolate and test

yes IM aware some guys would rather dig out their eye with a red hot fork than to read links, but if you take the time to actually research the problem and isolate and test you,ll soon find the answers

well the first thing you do is pull trouble codes
and it would help if you purchased a shop manual.


yes a decent infrared temp gun is a helpful diagnostic tool
keep in mind , even if everything running well,
the front two cylinders tend to run a small amount cooler (20 degrees) simply because the increased cooler air flow over the header tubes
the actual exhaust gas and header temp will vary with the combo specs , your looking for consistency not a specific temperature at the exhaust ports




these related links should also help check for fuel nrail fuel pressure, check your getting a pulse on both banks of fuel injector pigtails with a NOID LIGHT TESTER
YOUR GETTING IGNITION SPARK, easily done, pull an ignition wire off the easiest to reach spark plug, insert a phillips screw driver into the spark plug wire and hold the insulated handle so the steel shaft of the screw driver is about 3/16" from ground and have a buddy try to start the car, you should see intermittent spark arcs from the gap between the screw driver and ground, It certainly won,t hurt to pull and inspect the spark plugs, if they don,t look to be in good condition replacing them is almost mandatory, if you see coolant or rust on a spark plug this strongly suggest a blown head gasket

checking your firing order and ignition timing can be critical, so do the required checks,
youll also want to verify the valves are properly adjusted,


L98/ TPI Engine Start Sequence
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).

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.


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.
youll find a hour or so reading thru the links and sub links, on this site in the threads, will provide a great wealth of related info and incite into related factors, or the function or testing of sensors, that you may not currently be thinking about, or things that you might not think that are related to your issue that PROBABLY ARE

without testing your simply guessing READ THE LINKS AND SUB LINKS AND THINK LOGICALLY... AND ASK

Last edited:
Ive found the most common problem a lot of guys face when working on the cars they own,
is that many guys seem over whelmed,mentally intimidated.
this tends to make a few guys reluctant,
to even begin looking through the potential reasons,your having problems,
in a documented step-by-step & logical manor.
this is silly, simply because theres not a damn thing a reasonably skilled hobbyist can not resolve,
once he locates the cause by the process of test and eliminate.
Even, knowing that, and they don,t want to think things through,
and go through a logical check list of what might be the source of the problems.

and yeah many guys erroneously just assume its a huge major problem ,
like a blown head gasket or a busted valve if the engine starts running badly.
in many cases, problems can be traced too,
a defective sensor, blown fuse or clogged filter or just the engine needing a long over due oil change and tune-up,
and maybe new spark plugs and a fuel filter can cure the issues.
your way ahead if you have a factory shop manual, and logically think things through.
yes a code reader, a multi meter , and checking things like for vacuum leaks does mater.
I got called over to help a friend start his 1995 corvette that had been sitting unused for almost a year,
he could not get it to start, the first thing I did was check all the fuses and battery voltage , the engine had ignition spark so I opened the shrader fuel, pressure
I asked him if the fuel gauge showed any fuel, he looked at me funny then said.. "
you mean I spent all day trying to get the car started and its simply out of gas?"
I said, never assume, deal in known facts...
lets try putting in 5 gallons of fresh fuel and see if it changes your results,
you guessed..
it fired right up with 5 gallons of fresh 93 octane and a can of injector cleaner poured in the fuel tank!
If the electrical system needs work or mods...its all part of the learning process and while frustrating in most cases its also forcing them to think through options,
make adjustments and learn how components function.




related info


good 60/40 lead/tin solder ... ux&FORM=EG
solderv.jpg ... d=12582872



related ... 61527.html
16dbd753-4d4c-40ea-9451-0dbc27426fe0_300.jpg ... 819657-_-N
70222843_large.jpg ... U=70222843
70222844_large.jpg ... U=70222844
the threads have links youll need
Last edited:
I got ask to help diagnose a problem on a guys 1988 corvette this morning,
he was convinced he had a bad main bearing and had thrown a connecting rod, when driving last evening,
he had been driving leisurely at about 40 mph, when the engine started knocking and the engine lost considerable oil pressure,
and started running rather roughly!
he had , had the presents of mind too, have the corvette towed home,rather sustain or contribute to further damage.
I go over to his house , at his rather urgent verbal prodding.., I looked things over, a bit and suggested we pull the valve covers.
he was really depressed thinking he needed a new engine.
well the removal of the valve cover on the drivers side showed a cracked stamped rocker
the exhaust rocker had broken and the lifter had lifted up in the block, enough in the lifter bore just enough to exposed the blocks oil supply , lifter passage when the push rod came loose.
what the result was, was far less traumatic engine damage than he had feared ,
I suggested he install a new roller lifter push-rod and rocker
looking with a flash light through the push rod guide slot showed something rather similar to this,
(pictures previously posted in a different thread below)
obviously ,removing the TPI intake is required. too do the repair,
and inspecting the cam lobes, and all the other rockers, during the process,
would be smart,
but it appears that it was simply fatigue wear on a rocker,
the vettes got over 140K miles and from the evidence it could use more frequent oil and filter changes.

Last edited:
how many of you gentlemen help other car owners..
How many of you can do basic maintenance if the cars dash shows a indicator light,
or starts making a "NOISE, or ACTING ODD?" how many of you guys work on the cars they own,
and have the basic tools and knowledge to do that ?
If you own a car, a few really basic tools like a floor jack, Jack stands,
a drill press,screw drivers,pliers, basic wrenches ,ratchets sockets,and a multi meter,
vacuum gauge, allen keys an assortment of hammers clamps a drop light, etc.
, should be in every guys garage.
I honestly am rather amazed at the number of people I know that don,t have the basic skills,
and knowledge required to work on a car and do basic maintenance like a tune-up,
brake job or pull codes on the newer cars that have computer controls.
one of the guys I know in my neighbor hood seems too be amazed that old geezers LIKE I AM,
can not only do a brake job, and change spark plugs but that if a service engine light comes on,
I'm not on the phone trying desperately to scheduled a visit to the local dealership.
Now theres lots of things I can,t easily do ,
due to a lack of the correct tools, like easily dismount and remount and balance tires,
but he thinks its bordering on black magic if I can use a code scanner and multi meter,
to locate a defective sensor.

the symptoms sound a great deal like the fuel pressure regulator is defective,
you might also want to check,
exhaust back pressure as clogged catalytic converters cause issues,
and replacing the oil pressure switch near the base of the distributor is a good idea,
if its over 5 years old
what year is your corvette?

related and useful links, if your tracking down a TPI tuning,
or idle or slow start issue


watch video

Last edited:
Can't say I'm surprised, everyone has there own nitch and mine doesn't have to be theirs. I WOULD expect
everyone to know about adding and changing oil, change wipers and headlight bulbs ..... etc.
Kinda quiet on Digital Corvette.
No C8 yet Grumpy.
Horsepower race is on.
Guys are deciding for themselves.
Big G likely to go Twin Turbo in the SS Impala.
New Engine Build.

Those Hip Hop 32 guys Running real fast.
I know the Vette Guys do not like it one bit.