help i cant take it anymore....

Discussion in 'Engine: Repairs and Modifications & generally corv' started by crackerjacked, Sep 26, 2018.

  1. crackerjacked

    crackerjacked New Member

    my 96 is backfiring bad enough to make it die when switching into gear. got new plugs , wires, maf sensor , throttle pos sensor, and i know how to get them off the dash .just dont know what dc, po,p means
  2. Maniacmechanic1

    Maniacmechanic1 solid fixture here in the forum

    You need to pull up DTC Codes from your 1996 C4 Corvette.
    Start there.
  3. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    without pulling trouble codes and testing your simply guessing at best,
    break the issue down into separate issues,
    check ignition strength and timing,and voltage
    check fuel supply/delivery pressure and volume
    check cam timing and cylinder compression.
    check valve train control and valve adjustment
    check firing order and spark plug gap
    check the valve lift, and for work lobes
    check for vacuum leaks
    adjust your iac and tps
    check your exhaust back
    verify sensors correct function
    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.


    the correct matching SHOP MANUAL
    keep in mind the basics you need to verify the fuel pressure is at about 40 psi if your dealing with a C4 corvette,
    you should NOT have significant exhaust back pressure, clogged catalytic converters,
    are a common problem on older c4 corvettes,
    verify the fuses are not blown, the trouble codes do not show any problems,
    all electrical grounds are reading good,
    verify theres at least 14.5 volts at the battery while its running, so you know the alternator functions,
    and all the injectors are functional with a noid light,
    all cylinders should read within 10% and show about 150 psi or greater.,
    on a compression test, verify the firing order,
    set the spark plug gaps at .045 ,
    and verify all the listed sensor values,
    verify the cam lobes are not worn, verify you have at least 10 psi of oil pressure per 1000 rpm.verify theres no vacuum leaks

    [​IMG] ... ermometer/
    Wide temperature range from -58 to 1832°F (-50 to 1000°C)
    you might have clogged catalytic converters, the ignition timing may be way off, you might have a worn out cam, the fuel pump may be defective, some injector(s) may be defective,check the alternator out-put check the fuel rail pressure use a noid light on the injector wiring, check the fuses,
    Ive found that the one most commonly over looked in my experience is that the stock exhaust system, is highly restrictive, especially if the catalytic converters are partly plugged and the stock fuel delivery system is not adequate,for the potential power, the heads and intake, allowable air flow potential, are all restrictive, and the stock cam timing and lift is already near max as it was designed to produce about 260 hp,and operate at under 5700 rpm, if you try too add an additional 100-200 hp, and 1000 rpm-2000 rpm to the engines power band, and too the engines output youll quickly find this to be a factor.
    I've also occasionally seen guys, improperly index or install a cam without degreeing it in correctly and thus have power band limitations.
    Id suggest you buy a factory shop manual, multi meter and a timing light, fuel pressure and vacuum gauge and start checking.:thumbsup:

    reading these links will be helpful
    yes I know it will take some time and effort to isolate and test
    but its the only 100% sure route to finding and fixing your problem,
    don,t get over whelmed,
    simply break the problem down to testing each basic sub system,
    test each related sensor and electrical component and electrical sensor and connection.
    some reading on the threads posted below, a bit of logic and deductive reasoning, and a multi meter and a shop manual will go a long way toward finding and fixing the problem.

    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


    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 is the most consistently accurate I.R temp gun I've used for testing[/img]
    [​IMG] - Bing Shopping - Extech&utm_term=1100200223789&utm_content=All Extech Products
    you always need a base line to start from, on a corvette.
    a logical step by step approach and keeping accurate notes helps.
    youll NEED a multi meter, a shop manual
    and a timing light and fuel pressure gauge at a minimum,
    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 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


    Last edited: Oct 8, 2018
  4. crackerjacked

    crackerjacked New Member

    well the only codes is 61 64 passkey code......
  5. Maniacmechanic1

    Maniacmechanic1 solid fixture here in the forum

    Suspect a defective Mass Air Flow sensor.
    Further testing is required.
    Procedure is covered in the GM Factory service manual.
    Should also be on Grumpys huge data base here.
  6. crackerjacked

    crackerjacked New Member

    you were right after two months of fighting it . thank you

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