Randomly dies

Discussion in 'Domestics' started by Chuck, Dec 17, 2017.

  1. Chuck

    Chuck Sr. Member

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    I will definitely be trying that today.
     
  2. Chuck

    Chuck Sr. Member

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    Well I tried the jump test you recommended and when it died the pump was still running.
     
  3. billr

    billr wrench Staff Member

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    When the pump was "still running", did you check to see if the FP was still OK? That's why you need to attach a gauge and leave it there for a while.
     
  4. Mobile Dan

    Mobile Dan wrench

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    Another low-tech test, if you haven't done it...after starting, you release key and ignition switch springs back to "On". With engine running, rotate key a scoch towards off and a scoch towards crank. Gently, slowly. Engine keep running?
     
  5. Mobile Dan

    Mobile Dan wrench

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    Another test would be to rig starter to crank engine without disturbing a suspect ignition switch. Connect a jumper to starter solenoid or maybe starter relay. A "pre-test" would be to turn key to ON and then crank engine with your jumper. Cranks but won't run? Well, I guess this test won't work. Cranks and runs? Great...now shut down, restart with key, let it run till it quits. Quit? Don't touch the key, don't slam the door, and the hood is already up, I hope. Now crank with your jumper. Cranks but won't run? Suspect ignition switch or associated connections. Cranks and runs? Suspect computers ability to operate coil or injectors.
     
  6. Chuck

    Chuck Sr. Member

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    Tried this test just now. No premature dieing.
     
  7. Chuck

    Chuck Sr. Member

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    Unfortunately the guy that tested it for me the other day has called in both yesterday and today and the only reason I haven't done a FP test at home is that I don't have the gauge for it and buying or even renting one at this time is not financially doable.
     
  8. Chuck

    Chuck Sr. Member

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    I have been able to remove the Ignition control module, ignition coil, ignition switch, fuel pump, and fuel filter as possible culprits.
     
  9. Mobile Dan

    Mobile Dan wrench

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    Is your fuel system TBI, MPI, or CFI? (two injectors, eight injectors, or the "spider injection" inside the intake manifold) Is your distributor cap the small one or the fat HEI? I'm having trouble finding info on your old truck. Have you done a (gentle) wiggle test to ECU connectors and a ECU "tap test"?

    :edit: Looking back at previous posts, looks like you have the TBI system.
     
    Last edited: Dec 20, 2017
  10. Mobile Dan

    Mobile Dan wrench

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  11. Mobile Dan

    Mobile Dan wrench

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  12. Chuck

    Chuck Sr. Member

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    Yes, it's the TBI system. I will check the ECU as soon as I can today. It is the newer style HEI were the coil is mounted separately from tthe distributor
     
  13. Chuck

    Chuck Sr. Member

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    does it mean anything when I disconnect the oil pressure switch, run a jumper wire across, start the car, disconnect the jumper wire and the car continues to run?
     
  14. nickb2

    nickb2 Wrench. I help when I can

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    In principle, logic tells me that the ECM should shut down fuel pump after two seconds if the ecm does not receive reference from the crank sensor. The oil pressure sensor is a back up source of power should the fuel pump relay circuit fail. This is a safety feature which I think GM did away with altogether. It would be normal for the engine to continue running if oil pressure sensor is unplugged if the fuel pump relay is still on.

    Looking at my post in # 13 of this thread, I was wrong to write that. The oil pressure sensor is not a fuel pump cut off switch. It is merely a back up system, once the oil pressure has gotten up to about 4psi, it is now a second source of power to FP.

    Many apologies for that error of mine.
     
  15. Chuck

    Chuck Sr. Member

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    No, worries. But the only issue with current logic is that I believe this truck was built before crank sensors were used in anything bigger than an S10. I could be wrong though.
     

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