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Thread: obs to 4.8 wiring

  1. #11
    Join Date
    Jul 2010
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    Douglasville Ga
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    224
    Sorry man im lost. Was your obs not an auto truck with a p/n switch on the column. Don't understand why you used a seperate relay. Also what is the function C1 39?

    Obviously the pcm is not able to pull that pin low enough to energize the relay since your meter reads partial system voltage during a crank attempt. If I understood what you are doing, maybe I could help.

  2. #12
    Join Date
    Jun 2011
    Location
    College station tx
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    It was an auto and i'm using the stock relay just rewired it to be like the 03 and c1 39 is starter relay control according to the wiring diagram it is supplys ground to the starer relay.

  3. #13
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    Jun 2011
    Location
    College station tx
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    So i noticed that i have 10 volts on the case of the pcm with key on

  4. #14
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    Jul 2010
    Location
    Douglasville Ga
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    Quote Originally Posted by wayoung View Post
    It was an auto and i'm using the stock relay just rewired it to be like the 03 and c1 39 is starter relay control according to the wiring diagram it is supplys ground to the starer relay.
    Hmmmm. Never tried it that way. I literally run the stock purple starter wire from the ign switch straight to the starter, nothing else.

  5. #15
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    Jul 2010
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    Quote Originally Posted by wayoung View Post
    So i noticed that i have 10 volts on the case of the pcm with key on
    Wow... I think you have made a fundamental mistake somewhere. Do a voltage drop test on your ground leads at the battery. You should have a lead going to the engine block, body, and frame. The pcm board doesn't groung to the case. I assume you have the case mounted in a way that grounds it? That's ok, but that sounds like you don't have a good ground to the body or whatever you have the pcm mounted to. This is weird...

  6. #16
    Join Date
    Nov 2003
    Location
    Denton Texas
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    Wow, if your case is energized with 10v when the key is on you have something seriously wrong in the wiring or the PCM is toast.
    See my truck data in the "My Garage" section here... http://www.ls1truck.com/forums/my-ga...tml#post191709

  7. #17
    Join Date
    Jun 2011
    Location
    College station tx
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    I'll check the pcm ground with a voltage drop test tomorrow,pcm isn't mount still need to send it off for tune, just wanted to make sure wiring was right first and i hope the pcm isnt fried.

  8. #18
    Join Date
    Jun 2011
    Location
    College station tx
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    So I pulled the comp off the harness then checked voltage at each pin on the harness and found 10.6V on all my grounds and the OIl level signal, and 9.6V on the VSS signal. So I guess I'll have to go through the harness now for a short.

  9. #19
    Join Date
    Nov 2003
    Location
    Denton Texas
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    Follow your harness and see if you pinched it anywhere, like the cam position sensor wiring between the transmission bell housing and the block. It's easier to do that you think.
    See my truck data in the "My Garage" section here... http://www.ls1truck.com/forums/my-ga...tml#post191709

  10. #20
    Join Date
    Jun 2011
    Location
    College station tx
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    wow this sucks i shake the harness at back of block and it goes between 0V and 12V at ground and then take the harness apart there, and can't find anything and wont go back to 0V.
    Last edited by wayoung; 12-28-2011 at 06:01 PM.

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