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Thread: LT1 trouble shooting help

  1. #11
    The LT1 beat me last year. Once they start acting up it's hard to figure out the problem (within CMC rules). I was always finding broken things but they would never solve the problem.
    CMC #50

  2. #12
    Senior Member Carroll Shelby
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    Lift the Fuel rail above the intake with the injectors and lines still attached, disconnect the coil connector (the control/thin wires, not the plug wire) to stop spark, and see if all of your injectors are spraying correctly while cranking the motor over with the ignition on. Keep all ignition sources away from the engine bay so put the vape and cigarettes away and make sure all of your spark plug wires are still connected with the coil disabled by disconnecting small low voltage connector.

    If you see an injector that is not firing, it is either clogged or not getting a signal to fire; swap it to another position to verify the issue.

    Autozone also has a Noid light set on loan a tool that you can plug into each injector connector to verify it is getting voltage to the injector (can't check with a voltmeter because it is a PWM signal).


    I know clogged injectors were an issue for you in the past from your donor motor, but if you used the old/donor fuel rail with your good injectors from your original motor, the old fuel rail WILL shed varnish and clog up the good injectors.

    All post-filter fuel injector/rail/hose parts need to be cleaned if they came off a non running car. This was an issue for me in the past as I even did my injectors and rail, but the supply hose kept shedding varnish and clogging my injectors.
    Last edited by Pranav; 06-22-2018 at 03:29 PM.

  3. #13
    Quote Originally Posted by Sook View Post
    Were the dead cylinder's exhaust tubes getting hot? I've been fooled by the injector test before.

    Disassemble the whole intake path, I had a MAF clogged with rubber at cresson. How are the O2 sensors? Maybe lost a sensor and is in limp mode?

    Skipped timing chain??
    Got it... ya there may be a sensor issue. I am hoping codes can point me in the right direction. If that is the case. I did not even think about the timing chain but that could make sense.

  4. #14
    Quote Originally Posted by Pranav View Post
    Lift the Fuel rail above the intake with the injectors and lines still attached, disconnect the coil connector (the control/thin wires, not the plug wire) to stop spark, and see if all of your injectors are spraying correctly while cranking the motor over with the ignition on. Keep all ignition sources away from the engine bay so put the vape and cigarettes away and make sure all of your spark plug wires are still connected with the coil disabled by disconnecting small low voltage connector.

    If you see an injector that is not firing, it is either clogged or not getting a signal to fire; swap it to another position to verify the issue.

    Autozone also has a Noid light set on loan a tool that you can plug into each injector connector to verify it is getting voltage to the injector (can't check with a voltmeter because it is a PWM signal).


    I know clogged injectors were an issue for you in the past from your donor motor, but if you used the old/donor fuel rail with your good injectors from your original motor, the old fuel rail WILL shed varnish and clog up the good injectors.

    All post-filter fuel injector/rail/hose parts need to be cleaned if they came off a non running car. This was an issue for me in the past as I even did my injectors and rail, but the supply hose kept shedding varnish and clogging my injectors.
    Ya, good call on the fuel rail. Man that just sounds like an accident waiting to happen. Lol.....

  5. #15
    Senior Member Carroll Shelby
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    Lol you can take some baggies or something and cover up the injectors so the fuel doesnt go everywhere.

  6. #16
    Quote Originally Posted by Pranav View Post
    Lol you can take some baggies or something and cover up the injectors so the fuel doesnt go everywhere.
    Ah great now I am building a weak compression chamber. Boom!!! See ya'll on the other side.

  7. #17
    Senior Member Carroll Shelby Fbody383's Avatar
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    Sean reminded me we had a similar issue at Houston in January. Before we started swinging parts we borrowed Casey's laptop and his scanning software. We found that the PCM engine temp signal was sketchy - you could wiggle it and see it drop out. I think we changed pigtail and sender.
    #39 CMC Camaro
    Orange is Fast!
    CMC-NT01 FTW!

  8. #18
    Senior Member Rookie 39PitCrew's Avatar
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    Quote Originally Posted by Fbody383 View Post
    Sean reminded me we had a similar issue at Houston in January. Before we started swinging parts we borrowed Casey's laptop and his scanning software. We found that the PCM engine temp signal was sketchy - you could wiggle it and see it drop out. I think we changed pigtail and sender.
    Yep. That's what we did. Computer was jumping back and forth between open loop and closed loop because the
    temp it was seeing was jumping between -40F and ~210F which really messed with the timing. Turned out to
    be a damaged wire a couple inches from the factory connector. The insulation had been cut and the wire was
    all corroded about an inch in each direction. Eventually the wire had broken inside the insulation.
    --
    ------__o
    -----_\ <,_
    ----(_)/ (_)
    Laissez les bons temps rouler

  9. #19
    Was hoping to be able to hook it up today but nice, waiting the cable. Should know being in Wednesday or Thursday, will know more then.

  10. #20
    Senior Member Carroll Shelby Supercharged111's Avatar
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    Are you using all OEM ignition components? Any aftermarket bits are garbage. ICMs especially, Blow Reilly's will sell you the same POS for a 93-97 LT1 and GM spec'd 3 different ICMs: 93, 94-95, 96-97. They all have different curves and none of them match the aftermarket stuff from what I've read. Now an ICM is more of an item that either works or it doesn't, so doubtful it's the smoking gun for this but I am inclined to leaning toward wiring or electrical/engine management if the compression is solid. We had an LT1 here that also had a bad pigtail for the coil so the car would just randomly die and gave no indication on the scanner WTF was going on.
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