Engine runs for a few seconds then dies

Discussion in 'Diagnostic & Repair Tech' started by Limey, Dec 18, 2017.

  1. Limey

    Limey New Member

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    Hi everyone
    I need some help to diagnose some starting problems.

    I have transplanted a previously perfectly operative 1uzfe from a 96 LS400 into my 50s Chevy pickup, and I excitedly tried to start it for the first time today.

    It starts, but only runs for a few seconds. If I open the throttle during starting it revs up but still dies in seconds.
    After it dies it will not start again until I turn the ignition off and back on again. If I don’t do that, and just turn to start from ignition on it won’t fire at all.

    The engine was stood for nearly two years before this starting attempt.

    I have got an external fuel pump, but still under control of the standard ECU. The pump remains powered for the whole process.

    I suspect that the spark is being shutoff by the ecu for some reason, and is only re-established when the ECU is power cycled.

    I am using the LS400 instruments, and the revcounter shows the idle at circa 1000 rpm for a second or so, it then rises to about 1300 then the engine dies.

    Any ideas?

    Thanks in anticipation
     
  2. gloverman

    gloverman Active Member

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    Try running on Engine start. After sitting the injectors often seize. If so give them a gentle tap with a screwdriver or likes until the click again. Once running I would have them serviced.

    This model the AFM signal issue could cause your issues. People often miss the 12 volt supply to the AFM when wiring. Check this is present.

    Another option is check the ignitors are well earthed. They dont have a earth in the wiring. Then check the plugs onto the coils. If one is loose or damaged giving poor contact it will display your symptoms. Next thing I would do is replace the coils.

    Good Luck.
     
  3. Limey

    Limey New Member

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    Thanks for the advice Gloverman.
    I have grounded the ignitors, and when it does run its on all eight, smooth and even, so I think I can eliminate the coil or injectors as being the issue.
    What does the AFM do?
     
  4. gloverman

    gloverman Active Member

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    If there is a fault with the feedback loop of the coils it will turn all eight injectors off - Its a built in feature of the ECU to save the converters if a misfire occurs.

    The AFM gives a signal to the ECU of how much air (mass of air) is entering the engine and is the primary input for fuel calculation. Without it most of the time the Gen2 engines fire then stop a few moments later.
     
  5. Limey

    Limey New Member

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    Answer my own question .... Air Flow Monitor.
    I’ll check the connections.
     
  6. American Locomotive

    American Locomotive New Member

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    Hi, I know it's a little late, but we had the same problem. Turned out the timing jumped 1 tooth on one cylinder bank. Engine would start and die. If you unplugged one cam sensor, it would keep running. Verify your timing.
     

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