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Motor will crank but not fire!

This is a discussion on Motor will crank but not fire! within the General Help forums, part of the LSx Technical Help Section category; Alright Guys, here is the background. The motor is a 5.7 out of a 98 Firebird with an auto. It ...

  1. #1
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    83 jeep scrambler

    Motor will crank but not fire!

    Alright Guys, here is the background. The motor is a 5.7 out of a 98 Firebird with an auto. It is now in a 83 jeep scrambler with a manual. I cut out all of the wires I did not need (AC, EVAP, Emissions, Etc.) and had the computer reprogrammed as such. I hooked up the PCM Battery Feed to constant battery through a fuse. I hooked up the PCM Ignition feed to Ignition power through a fuse. I hooked up all fuel injectors and electronic ignition control modules to ignition power through a fuse. I turn the key and the motor cranks but will not fire. I think I am missing steady spark. What am I missing here? I have oil pressure and fuel pressure. I pulled all the plugs and they are getting fuel. Please Help!!!!

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    if you have fuel and spark the engine has to atleast try to fire, if you say its cranking but its not turning over is gotta be spark related, try checking the sparkplugs make shure you have the right gap.

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    Moderator Cutlass's Avatar
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    did you get the PASS-KEY theft deterrent programmed out? The PCM is looking for a fuel enable signal from the BCM. It should only effect fuel, not spark though.

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    make sure that you have all the connectors hooked up on the engine, all it takes is one connector to be unhooked and it may not start, such as the cam sensor, etc

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    Veteran 0rion's Avatar
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    Quote Originally Posted by Cutlass View Post
    did you get the PASS-KEY theft deterrent programmed out? The PCM is looking for a fuel enable signal from the BCM. It should only effect fuel, not spark though.
    I agree, did you address vats when doing the swap?

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    Nitrous Tuner LS2Tuner's Avatar
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    Quote Originally Posted by 0rion View Post
    I agree, did you address vats when doing the swap?
    Sounds like the vats system is active.
    Don't be afraid of the bottle!!! Be afraid of your tune!!!

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    Thanks

    Thanks for the input guys. I found that the PCM IGN Feed was not getting power during cranking, so I jumped that wire straight to the battery and the motor fired up immediatly. Now it just runs for 2-3 seconds and stops. I had the ECU programmed about a year ago and don't remember if I told the guy I wanted it removed or if I wanted to build a bypass. Bypass it is I guess.

  8. #8
    Nitrous Tuner LS2Tuner's Avatar
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    I would look at the fuel pressure now to see if it is staying high enough after the initial fire and run.

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    Vats does that, if a theif manages to start the car the PCM shuts off fuel delivery.

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    Bypass Module

    Alright. I built my VATS bypass according to the diagrams and instructions on the corvette forum guys writeup. I am positive I am getting the 5v but not sure on the 50hz. Either way, when I wire it to Pin 11 on the pcm (theft deterrant) it still only runs for 2 seconds. Pin11 on the PCM use to run to the body module. Am I missing something else? I have a 98 motor, would it be looking for a different hz?

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    Moderator Cutlass's Avatar
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    Wow, I never know there was a VATS bypass like that. Yeah it should be pin 11 on Connector 1 (RED).
    I did some research and it appears you're correct it needs a 5V 50Hz signal. Verify the 50hz, most likely thats your problem.

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    Whoo HOOO!!!!!!

    She RUns!!!

    I just thought I would give something a try. I hardwired the fuel pump directly to the battery via a relay. Cranked it and she runs and runs strong!
    My VATS bypass module worked !!! 5v 47.1HZ!!! Thanks for all of your guys help. Mow I just need to figure out this wiring mess!

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