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Thread: Is my PCM bad?

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  1. #1
    Join Date
    Oct 2004
    Posts
    259
    Hey guys Ive been pretty busy this last couple of months but is time to get back on track and get this truck running.
    Is there a chance my PCM could be bad? Theres power going to it and the motor cranks. There's no spark and the fuel pump will not kick on unless I hot wire it. All those things are controlled by the PCM and the damn is grounded right, theres no break in the lines, no blown fuses. This is all I can think off, I even took off the wiring harness and went through everywire and every pin in the PCM.

    Well in another note Ill be a civilian come monday the 7th of August and I will be moving back to the great state of TX. Thats the big rush in getting this thing running. Ill will be sending my PCM to Allen first thing monday morning. Well Ill talk to you guys later.
    Had a 91 SB, Open diff, 3.08 gears, stock LS1/T56. 14.8@95.9...sold.
    Now, 90 C1500 350tbi/NV3500....just bought a 5.3...need T56, Swap parts.....

  2. #2
    Join Date
    Nov 2003
    Location
    Denton Texas
    Posts
    20,540
    Couple things to check, check the grounds, check that you have power to the pcm connectors at all the red and pink connectors. Red 12v all times, pink 12v with switch on. Did you put an inline switch somewhere to keep an unauthorized person from driving the truck while you were away? You may have to pull the fuel rail out and see if the injectors are firing. They will seize up if they sit a long time dry. Turn them upside down and tap them on something firm to unstick them if fuel doesn't spray out of them when you have power at everything.
    See my truck data in the "My Garage" section here... http://www.ls1truck.com/forums/my-ga...tml#post191709

  3. #3
    Join Date
    Oct 2005
    Location
    Baton Rouge, LA
    Posts
    997
    I had an issue when I first tried to crank the truck. Make sure the power going to the injectors are greater than 9V. I had too much pulling from that circuit (gauges & interior lighting... don't ask&#33 causing the injectors not to function at full capacity. Took the fuel pump, and ran off a seperate circuit, then all fired up as should. Just a thought. Good luck!
    Test-n-Tune (Nov 23, 2008) - 13.65s @ 98mph

  4. #4
    Join Date
    Oct 2004
    Posts
    259
    The truck was running recently. I took off the wiring harness to relocate the PCM. After I put the wiring harness back on it wouldnt start, but I really didnt change to the wiring. Is the same set up as the one when it was running. Then I took off the wiring harness off again and checked all the wires and fuses to make sure nothing was wrong.

    I isolated the engine harness from everything else. So there's nothing else hooked up right now, no lights, horn or fans at that. The only things with power right now are the engine sensors, injectors, coils, PCM and starter. The spark plugs are brand new and after all that cranking they still look like they just came out of the box. So I know Im not getting spark or fuel. If I hot wire the fuel pump I get fuel at the rail but not out of the injectors, I dont think they firing because they are not getting a signal to fire from the PCM. Hence I think the PCM is burnt or something.
    Had a 91 SB, Open diff, 3.08 gears, stock LS1/T56. 14.8@95.9...sold.
    Now, 90 C1500 350tbi/NV3500....just bought a 5.3...need T56, Swap parts.....

  5. #5
    Join Date
    Oct 2005
    Location
    Baton Rouge, LA
    Posts
    997
    What level of voltage are you getting at the IGN fuses? How is your wiring set up? Do you have a stock harness, custom harness, etc?
    Test-n-Tune (Nov 23, 2008) - 13.65s @ 98mph

  6. #6
    Join Date
    Nov 2003
    Location
    Denton Texas
    Posts
    20,540
    That sounds like either the crank position or cam position sensors are not connected or have a short.
    See my truck data in the "My Garage" section here... http://www.ls1truck.com/forums/my-ga...tml#post191709

  7. #7
    Join Date
    Oct 2004
    Posts
    259
    Ill check the sensors this morning, it should be 12 at the sensors right?

    As for the IGN fuses Im getting 12. Im runnin a stock harness, but I used it before and the truck ran fine. Ill keep you guys posted, thanks.
    Had a 91 SB, Open diff, 3.08 gears, stock LS1/T56. 14.8@95.9...sold.
    Now, 90 C1500 350tbi/NV3500....just bought a 5.3...need T56, Swap parts.....

  8. #8
    Join Date
    Nov 2003
    Location
    Denton Texas
    Posts
    20,540
    Sensors get 5V from the PCM.
    See my truck data in the "My Garage" section here... http://www.ls1truck.com/forums/my-ga...tml#post191709

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