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  1. #1
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    Jan 2011
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    Corvette(s)
    1993 40th White

    Default NO START/SHUTS OFF WHEN DRIVING, NO ECM COMMUNICATION - NEW ECM - WTH????? 6k LATER!!

    OK, my mechanic says it is the ECM, BUT after reading so many posts here I am beginning to wonder.


    New ECM, distributor, coil, heads, wires, plugs, starter, water pump, repaired ground wire on distributor, yadda yadda.

    Reson for heads? ECM causing car to overheat by not communicating to fan. No more overheat.

    Prior to repair car did same thing: As ..... EXTREMELY INTERMITTANT NO START, but then would start. EXTREMELY INTERMITTANT SHUTTING OFF WHILE DRIVING, not emberrassing as a darn MUSTANG passes you on the freeway.. UGH.. Would pull over and start. But appeared to be just a freak thing.

    Finally whatever this issue is has hit the bottom and now wont start at all.. FAULTY ECM?

    Mechanic says:

    "Car would not start. So we connected up tester to computer and disrtibutor for spark and fuel pump pressure tester to fuel rail. Fuel pressure was good, but, no spark command coming out of computer."


    He has said before that when they put fuel/gas up top they can get it started.

    MY CAR RUNS AWESOME WHEN IT RUNS. No sputtering or issues other than can't keep it running or get it to start now.

    93, stock anniversary automatic P series.

    I WANT MY CAR BACK, PLEASE HELP........ Before I deal with this ECM again. Any ideas? I just bought the damn thing in October, put it in last month, drove my car for about a week and that was it. Haven't had it for months with all the work that I've done. Throw me a Christmas biscuit guys :-) And I am a gal, pretty mechanically saavy mentally, don't turn wrenches, so be kind.

    LIG.... MTB for me no matter what!
    Stop and smell the roses, watch the sunrise and LIVE....

  2. #2
    Member
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    Dec 2008
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    texas
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    Corvette(s)
    87 z-51

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    Quote Originally Posted by TammyLS View Post
    OK, my mechanic says it is the ECM, BUT after reading so many posts here I am beginning to wonder.


    New ECM, distributor, coil, heads, wires, plugs, starter, water pump, repaired ground wire on distributor, yadda yadda.

    Reson for heads? ECM causing car to overheat by not communicating to fan. No more overheat.

    Prior to repair car did same thing: As ..... EXTREMELY INTERMITTANT NO START, but then would start. EXTREMELY INTERMITTANT SHUTTING OFF WHILE DRIVING, not emberrassing as a darn MUSTANG passes you on the freeway.. UGH.. Would pull over and start. But appeared to be just a freak thing.

    Finally whatever this issue is has hit the bottom and now wont start at all.. FAULTY ECM?

    Mechanic says:

    "Car would not start. So we connected up tester to computer and disrtibutor for spark and fuel pump pressure tester to fuel rail. Fuel pressure was good, but, no spark command coming out of computer."


    He has said before that when they put fuel/gas up top they can get it started.

    MY CAR RUNS AWESOME WHEN IT RUNS. No sputtering or issues other than can't keep it running or get it to start now.

    93, stock anniversary automatic P series.

    I WANT MY CAR BACK, PLEASE HELP........ Before I deal with this ECM again. Any ideas? I just bought the damn thing in October, put it in last month, drove my car for about a week and that was it. Haven't had it for months with all the work that I've done. Throw me a Christmas biscuit guys :-) And I am a gal, pretty mechanically saavy mentally, don't turn wrenches, so be kind.

    Can't have both.
    It either has NO spark therfore adding a Saudi oil well would not help it run...

    OR

    it always has had spark and the problem is FUEL delivery. If they "put fuel in the top(???)" and it runs...there IS spark. period.

    Your mechanic is not Corvette experienced is he? Just because there is fuel pressure does NOT mean the inj are getting the signal to pulse. That comes from a reference signal that originates at the distributer. Lots of wire inbetween. Does this shop understand how the EFI system on a Vette operates? thats critical.

    OK fuel pressure...got to be at least 40psi. Won;t run under 30. Steady pressure? Fuel system leakdown time? Anyone document that?

    New distributer...New OptiSpark? (cause thats what it sounds like dying on the road) or (fuel filter/pump)

    Has ANYONE tested the VATS module per FSM instructions ???

    The odds of your ECM being bad were slim. The odds of the new ECM being bad are astronomical. Out of tens of thousands of C4 models each yr I hear os a REAL ECM failure every once in a great while...rare.

    New heads because the ECM failed to manage the fans? Throwing the BS flag on that one....

    Fans are managed by relays and coolant temp sensors. The ECM is not going to prevent fans from working unless its just plain DEAD and nothing else works as well. It CAN happen but its pretty damn odd...
    So Its unable to run so its unable to get hot.
    Besides, if the engine got so hot to damage heads, the rings are likely burnt, cyl walls scored...other block damage. Was that too much work to include in the bill?

    I'm sorry...this don;t smell right. Throwing THAT much money at a simple problem is pretty unbelievable. Especially from a Mechanic.

    Its time to go back to basics...Starting with a FSM and someone that can read. A FSM is under $100 and would have saved you about $4000 I'm guessing.

    ANy codes present?

    Fuel pressure & regulator tested for flow and pressure?
    Inj ohms tested? Need to see 16 and no less than 12-14. THAT however is NOT definative...you might discover slow or weak inj. IF ONE died, or gets shorted the whole system CAn shut down....Try starting with 1 inj at a time UNPLUGGED.
    Opti replaced?
    EGR system checked?
    Grounds from harness checked? G-104 bundle specifically?
    Hot source wires and fusable links checked?
    Pos batt cable visually inspected behind the block?
    Harness visually inspected behind the block?
    VATS starter enable & VATS decoder module tested per FSM ? bypassed?
    What kinda shape is the column ign switch & switch rod on the column? That switch CAN do all this....

    Its not voodoo. The FSM has simple easy to follow flow charts and trouble trees that anyone can follow with some basic test tools and diagnose a no start or no-run condition. There is NO problem that the FSM does not have answers for. It IS after all, the factory BOOK on the operation of a Corvette spcific to that yr.

    For whats been spent, you could have bought me a r/t plane ticket, got the car fixed, paid me 1000 and had $2000 left over.....
    6K ? thats a new long block. A good one too.

    I don;t know what else to suggest...except a different pair of eyes (and hands) working on the car. Some eyes with a FSM.

  3. #3
    hotmtrsports's Avatar
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    Jan 2004
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    Lakeside in Monmouth, Maine
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    Corvette(s)
    76 L82 Auto, 05 Cpe 6spd

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    As "boomdriver" states...

    BACK TO BASICS...

    1st thing is to get a Factory Service Manual for your year car then simply follow the diagnosis step by step doing just as the manual suggests. No skipping, no cheating. The step you skip may be the one that gets your car back.

    Even if you just get the manual and read the suggestions, you'll be able to understand what is going on.

    AND probably try a different mechanic.

    Chuck M
    Doesn't everybody have a 4 post lift in their garage?

    Corvette Museum Founding & Lifetime Member #4125

    www.corvetterepairsofmaine.com

  4. #4
    Gone but not forgotten John Robinson's Avatar
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    May 2005
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    Muncie, Indiana
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    1,609
    Corvette(s)
    1993 Polo Green Coupe

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    Read this

    Throttle Position Sensor (TPS)
    Copied from 1993 Hope this sheds some light on the tps for you




    Service Manual
    The Throttle Position sensor (TPS) is a potentiometer connected to the throttle shaft on the throttle body. It is a potentiometer with one end connected to 5 volts
    from the ECM and the other to ECM ground. A third wire is connected to the ECM to measure the voltage from the TP sensor. As the throttle valve angle is changed (accelerator pedal moved), the voltage output of the TP sensor also changes. At a closed throttle position, the voltage output of the TP sensor is low (approximately .5 volt). As the throttle valve opens, the output voltage should be approximately 5 volts.

    By monitoring the output voltage from the TP sensor, the ECM can determine fuel delivery based on throttle valve angle (driver demand). A broken or loose TP sensor can cause intermittent burst of fuel from the injectors and cause an unstable idle, because the ECM detects the throttle is moving.

    If the TP sensor circuit is open, the ECM will set a DTC 22. If the TP sensor circuit is shorted a DTC 21 will be set. A problem in any of the TP sensor circuits will set either a DTC 21 or 22. Once a DTC is set, the ECM will use a default value for TP sensor, and some vehicle performance will return.

    A personal note, when my TPS failed it DID NOT set a code other than to tell me the ECM was bad.




    On my car the tps was telling the ecm the engine was flooded and so the ecm would not allow fuel to the injectors. And yes I also replaced the ecm only to find out it did not fix the problem. Make absolutely sure the tps is good and that the wires to it are not broken.(common problem)

    As others have said if you are not familiar with the Corvette system you can dump a ton of money in it. Either you have to get a FSM (Field Service Manual) and study it so you understand it or you have to pay someone with a long history of fixing Corvettes especially the C4. Another critical system is the grounds since the car is a plastic body. Dirty grounds will kill it quicker than anything else. Again a mechanic who has a history with C4 will know all about the grounds ans were they are located.

  5. #5
    Member gmjunkie's Avatar
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    Corvette(s)
    03 Z-51,78 L82 Coupe

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    Quote Originally Posted by John Robinson View Post

    Throttle Position Sensor (TPS)


    Good point John,I remember when you were going through that aggravating mess!~!

    I didn't see anywhere in this thread where the ignition module has been checked or replaced either,with the symptoms this vehicle is having I've seen "Ignition Modules" act the same way!
    junk!!
    "WARNING"
    The views and opinions of this forum user might not be suitable for others, this user may appear to be heavily over-medicated, under medicated, intoxicated, listening to the voices in his head or just plain being an ass, so some viewers may be offended!~!!!
    www.gmjunkie.com
    Founding Member: 10 Corvettes Anonymous


  6. #6
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    87 z-51

    Default

    I think at some point the 'dist' was replaced,....but I do not recall if that was the whole thing or pieces....She has pretty much replaced the motor at this shop thats doing her work. The 'problem' keeps reappearing......pretty good indication that nothings been fixed.

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