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Thread: LS1 Swap cranks, but no fuel and no spark

  1. #1
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    Question LS1 Swap cranks, but no fuel and no spark

    I have an LS1 swap into a kit car. It will crank, but it will not start. Some things of note:

    • It does not seem to command an injector pulsewidth
    • VATS has been disabled, and I performed a full write
    • Noid lights show no injector activity
    • Spark tester shows no spark
    • The fuel pump does kick on
    • With the exception of the IAT, all of the engine variables seem about right
    • MAF seems the same whether I'm cranking the engine or not.
    • I am running a cable throttle body



  2. #2
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    Try failing the MAF in the tune and see if it runs.

    You'd be suprised sometimes that the -38 intake temps could cause issues. If the harness was from the LS1, it would have had a 2 wire connector for it somewhere. The IAT were in the intake tubing on those cars.

    You can add commanded AFR and injector pulse width to your scans to make sure you can read them while you try getting it started.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

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    Quote Originally Posted by 5FDP View Post
    Try failing the MAF in the tune and see if it runs.
    What do you mean? Set it up as Speed Density in the Operating System menu? Sorry, I'm new to HP Tuners.

    You'd be suprised sometimes that the -38 intake temps could cause issues. If the harness was from the LS1, it would have had a 2 wire connector for it somewhere. The IAT were in the intake tubing on those cars.
    I don't believe I have the actual sensor. Could I bypass it somehow, or should I try to find one locally? Also, any idea what the 2 wire plug looks like?

    You can add commanded AFR and injector pulse width to your scans to make sure you can read them while you try getting it started.
    Done, thanks. I'll see if I get anything in the morning.

    BTW, I do have a CEL for an Evap code (since I don't have a charcoal canister), but I'm not sure if that matters or not.

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    Failing the MAF isn't something you have to upgrade the tune for. It would just be a test to rule out a bad maf, or you could just unplug the MAF and try again. Failing the MAF is easy, you'll be doing this anyway when you have to tune the VE table on this vehicle. Set the MAF fail high setting to 0hz under the engine diag tab, then set the 3 MAF dtc's to fail on first error instead of second error.


    You don't want to bypass the intake air temp sensor, it is used in all fueling/airflow calculations. You can just image search what a GM iat sensor looks like, that will tell you what the plug looks like.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

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    I have an LS1 camaro, I never drive it. Maf was dead last time I started it, ran pretty good. I'm not sure how failing the maf is going to get you an injector signal.
    Try checking the crank sensor and plug, and ohm the signal wire all the way back to the pcm.
    A missing iat wire tells me the harness could have other problems.

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    In fact, check all the sensors and maf for a 12 or 5 volt signal. Seems to be a common swap problem.

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    That's what I'm thinking. A bad MAF and no IAT might make it run poorly, but it should still start. The car has the wiring for the IAT (it's a stock 04 GTO harness), there's just no sensor to be found. I guess I'll grab one locally.

    I'll unplug the MAF anyway, just as a test. I'll also check the MAF. If it's like others MAFs, it should be a 5v signal.

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    Did you mess with the crank reluctor? is the crank sensor above the starter plugged in. I had a reluctor issue once and I know it wouldn't start but don't recall if injectors were firing or not. Just a guess

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    Quote Originally Posted by gearhead927 View Post
    Did you mess with the crank reluctor? is the crank sensor above the starter plugged in. I had a reluctor issue once and I know it wouldn't start but don't recall if injectors were firing or not. Just a guess
    I'll double check that, but I'm assuming that it's plugged in since I'm getting an RPM signal, yeah?

    I checked the cam sensor and that's plugged in.

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    I know it will start without a cam sensor but I am pretty certain no ignition or injector pulse without crank sensor working properly. I do not know what the pcm is reading for rpm though.

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    Quote Originally Posted by circuiticon View Post
    That's what I'm thinking. A bad MAF and no IAT might make it run poorly, but it should still start. The car has the wiring for the IAT (it's a stock 04 GTO harness), there's just no sensor to be found. I guess I'll grab one locally.

    I'll unplug the MAF anyway, just as a test. I'll also check the MAF. If it's like others MAFs, it should be a 5v signal.
    No, it's a 12 volt signal.

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    Also ohm out the sensor grounds. I'd say the crank sensor or it's wiring are most probable. Or ground since it's a swap.

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    Quote Originally Posted by gearhead927 View Post
    I know it will start without a cam sensor but I am pretty certain no ignition or injector pulse without crank sensor working properly. I do not know what the pcm is reading for rpm though.
    I would ASSUME that it's reading the crank sensor for RPM, but I guess it could be reading the cam sensor and multiplying it by 2.

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    Quote Originally Posted by Jason B View Post
    No, it's a 12 volt signal.
    Wow, that's different than what I'm used to. Ok.

    Quote Originally Posted by Jason B View Post
    Also ohm out the sensor grounds. I'd say the crank sensor or it's wiring are most probable. Or ground since it's a swap.
    Ok i'll do that.

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    Made a video for you. Battery voltage is 11.?? Like I said I never drive it - battery was low.
    https://youtu.be/nEoOkDiBzw0

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    I'm guessing you modified the harness for the cable throttle?

    Guess you also modified the programming?

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    Quote Originally Posted by Jason B View Post
    Made a video for you. Battery voltage is 11.?? Like I said I never drive it - battery was low.
    https://youtu.be/nEoOkDiBzw0
    Yeah, just as you said, runs fine without a MAF.

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    Quote Originally Posted by Jason B View Post
    I'm guessing you modified the harness for the cable throttle?

    Guess you also modified the programming?
    I modified neither. Any idea what I should do here?

  19. #19
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    04 GTO's run cable tb's still.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

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    New video.



    Things to note:

    • Fuel pressure is around 56psi
    • While cranking, I get an IPW
    • I picked up an IAT sensor and i seems to be reading properly
    • Unplugging the MAF didn't matter
    • Seems to have a cam signal
    • VATS Status: Pass
    • Oil pressure - 31psi while cranking
    • Oil level low - Yes (it has about 7 or 8 quarts in it with my larger pan and cooler)
    • On the MAF, Grounding @ pin B, pin A measures 4.99v
    • Tested all of the powers and grounds to the ECU's "blue" harness, and everything passed
    Last edited by circuiticon; 07-27-2017 at 11:33 AM.