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Thread: 1968 C10 5.3L LMG no start?????

  1. #11
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    injector or coil data does not change on scan tool while cranking.

  2. #12
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    I preformed a "full" reflash with vats off and still no start.

  3. #13
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    just reviewing my tune file and noticed the it was a type 2 vats patch. Should I try to reflash it as a type 3..
    Trevor

  4. #14
    Lifetime Member GMPX's Avatar
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    2 or 3 should work, either one sends the ECM down the right path.

    I thought even with the VATS still active, the engine will fire briefly, like 1/4 of a second just to let you know, yes everything is ok but I am not going to allow this engine to keep running.
    I also thought the request to crank was a discrete input not a GMLAN message (I think the discrete input is J1-52, but I don't know that is 100% correct). I confess, that is beyond where I normally deal with so I am not sure. The ECM does seem to get grumpy when the starter relay output is left open circuit (J1-67).
    Maybe post up your file too.
    Last edited by GMPX; March 15th, 2010 at 10:27 PM.
    I no longer monitor the forum, please either post your question or create a support ticket.

  5. #15
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    there is got to be a way to tell the pcm to start other then the GM LAN message from the bcm...... Is this PCM in an older vehicle that may not need a GM LAN message and has like a 12 volt input to the pcm to start...

    Trevor

  6. #16
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    Quote Originally Posted by GMPX View Post
    2 or 3 should work, either one sends the ECM down the right path.

    I thought even with the VATS still active, the engine will fire briefly, like 1/4 of a second just to let you know, yes everything is ok but I am not going to allow this engine to keep running.
    I also thought the request to crank was a discrete input not a GMLAN message (I think the discrete input is J1-52, but I don't know that is 100% correct). I confess, that is beyond where I normally deal with so I am not sure. The ECM does seem to get grumpy when the starter relay output is left open circuit (J1-67).
    Maybe post up your file too.
    Just for fun some OS's use J1-67, others J1-52. Seems J1-67 is earlier, J1-52 later. Vegasrobbi has had success with a resistor in circuit so it looks like it expects to see some idle current to ground.

    And to make it just a little more perplexing even some OS's that use this J1-52 crank relay control will start on the second crank and some wont.

    Will give it a shot this morning and report back.

    Unfortunately the request to crank is generated via the BCM which the ign switch connects to. There are no wired inputs in relation to this so can only assume it is one of those functions like cruise control that has disappeared into the mysteries of the GMLAN.

  7. #17
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    what do you mean by J1-52..... connector 1 terminal 52..

  8. #18
    Lifetime Member GMPX's Avatar
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    What about the GMPP standalone E38/E67, what do they use for crank request?
    I no longer monitor the forum, please either post your question or create a support ticket.

  9. #19
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    Quote Originally Posted by tk-mpl View Post
    what do you mean by J1-52..... connector 1 terminal 52..
    Yes the body connector. J1/X1/C1. The 73 pin item with including the larger ground terminal.

    Getting a relay coil on pin52 certainly seems to see the engine kick more, but not run as Ross mentions. Battery is dead now.... back into it after a charge.

  10. #20
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    Quote Originally Posted by GMPX View Post
    What about the GMPP standalone E38/E67, what do they use for crank request?
    They dont use a crank request. Direct connect to starter motor from key or key/crank relay.

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