Question about 1990 Chevrolet C1500

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My 1990 chevy pickup backfires when its cold. i punch it it stalls and pops. i think its the egr valve or solenoid. can someone help me?

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  • failo92104 Nov 12, 2010

    hi joe. i had an 88 cheyenne 350 tbi just like my silverado now with the same problem but alot more backfiring. i was told to disconnect the egr solenoid and plug the hose. i did and the backfiring stopped for the most part. you dont think its a vaccuum issue?

  • failo92104 Nov 12, 2010

    and by the way joe i dont think my truck has maf sensor. i was looking up replacement part prices and i didnt see any listing for maf sensors for my truck.

  • failo92104 Nov 12, 2010

    thanks for the reply vetteman. i was thinking of replacing the egr valve and solenoid. another symptom is that it only backfires when its cold. once the truck gets up to normal running temp it does fine. no stalling no backfiring. i dont know if that helps the diagnostic process.

  • failo92104 Nov 12, 2010

    ok. so disconnect one and start it up cold like wen i go to work in the morning and if it stops backfiring while that one is disconnected that should be the one thats bad?

  • failo92104 Nov 12, 2010

    Thank you very much vetteman you have been very helpful. I will try that and see what happens. What if I just replace all three sensors with new ones.

  • failo92104 Nov 12, 2010

    Ok. Thanks vetteman. I really love my truck and was worried it might be the end of the road for it having 280,000 miles on it. It runs like a champ though, starts right up even the ac works. Thanks again.

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This could be a few different problems. It could be the tps or throttle positioning sensor, the knock sensor, or like you said the egr valve. The easiest is to clean the egr valve. Make sure that it is clear.

Posted on Nov 12, 2010

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  • Rodney Clark
    Rodney Clark Nov 12, 2010

    Yes. I have seen all three of these cause this exact same problem. All three seem to only effect the engine when it is cold. You might try disconnecting them one at a time. And when it changes then this should help you find out which one is causing the problem.

  • Rodney Clark
    Rodney Clark Nov 12, 2010

    That is correct.

  • Rodney Clark
    Rodney Clark Nov 12, 2010

    You can do that. But I am sure that you will find that only one is bad. And if so. You could spend an extra $150 for nothing.

  • Rodney Clark
    Rodney Clark Nov 12, 2010

    No problem. I hope that you get it fixed. They are good ol' trucks. I love mine!

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Hello failo. Sounds like either the MAF sensor in the wiring harness is having a problem, or your engine wiring harness is simply old, dry and cracked and is shorting out somewhere. Both of these are extremely common and very likely causes.

Unfortunately as vehicles age, the plastic insulation used in the wiring harnesses gets dry and cracks, and then your wires have no insulation.

A good way to test to see if it's the harness or not is to pull each spark plug boot out, one at a time, and just set it on the top of the engine. Then start the car...if you don't see/hear a spark from that boot, then you know the harness is the problem.

A replacement harness and MAF sensor is a common part at the auto parts store. Call around to get the best price. Joe

Posted on Nov 12, 2010

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The EGR valve is mounted on the intake manifold and has an opening into the exhaust manifold.

The digital EGR valve, used on all 1990 and later EGR-equipped engines (Except the 2.5L and 1994-96 3.8L engine) is designed to control the flow of EGR independent of intake manifold vacuum. The valve controls EGR flow through 3 solenoid-opened orifices, which increase in size, to produce 7 possible combinations. When a solenoid is energized, the armature with attached shaft and swivel pintle, is lifted, opening the orifice.
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This system must be checked using a Tech 1®or equivalent scan tool. Steps 4, 5 and 6 must be done very quickly, as the ECM will adjust the idle air control valve to compensate for idle speed.
  1. Using a Tech 1®or equivalent scan tool, check for any diagnostic trouble codes and solve those problems first. Refer to the Diagnostic Trouble Code (DTC) lists later in this section.
  2. Select "EGR CONTROL'' on the scan tool.
  3. Start and run the engine, until it reaches normal operating temperature, then allow the engine to idle for 2 minutes.
  4. Energize EGR SOL #1; engine rpm should drop slightly.
  5. Energize EGR SOL #2; the engine should have a rough idle.
  6. Energize EGR SOL #3; the engine should idle rough or stall.
  7. If all tests were as specified, the system is functioning properly.
  8. If not, check the EGR valve, pipe, adaptor, gaskets, fittings, and all passages for damage, leakage or plugging. If all is OK, replace the EGR valve assembly.
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