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Thread: Pcm ground

  1. #51
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    DARREN BRANDON
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    I have been watching the playback a few times, is it normal of the 12 volts ignition to drop to zero while cranking?? Seens a bit odd..

  2. #52
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    DARREN BRANDON
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    Another update.. I found that the circuit in had the 12 volt switched for pcm into inside car drops voltage when starter engaged, so I connected direct to battery and now no longer Drop to zero
    Now I have a dtc 41 ignition control circuit open. The dropping of 12 volts explains why spinning opti by hand was giving me everything, but when cranking i had no pulsing at icm.. now to figure out the 41

  3. #53
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    Shes alive!!! Whilst testing agin she fired up... scared the crap out of me.. open exaust.... lol

  4. The Following User Says Thank You to Darrenmb For This Post:


  5. #54
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    happy for you! I just want to tell Injuneer that I believe it is highly appreciated how much effort you put into and patience you have when working with people on situations like this!
    -Ryan
    93 Z28 M28

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  6. #55
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    Fred
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    Thanks for the positive feedback. Funny thing is, these issues are seldom the same, and every time I work on a new problem, like this one, I learn something new - win-win situation. In this case it has me thinking about the fact there are two sources each of battery 12V, switched 12V, and grounds. How is the PCM divided internally to utilize the dual circuits. Are there two “halves” to the controls?

    And, the problem showed up in a scan of just a few seconds of cranking a non-starting engine. Never underestimate the power of a data log. Amazing what can be lurking in there.
    SOLD - GONE TO A (VERY) GOOD HOME ! - 94 Formula A3+1: 381ci forged stroker - Callies Stealth, Oliver 5.85 billet rods, BME nitrous pistons / CNC LT4 heads / CC solid roller / TH400+GearVendors OD / 4.11 Strange 12-bolt / 300-shot N2O / Spohn Suspension / roll bar / MoTeC M48 Pro engine management system /a few other odds 'n ends.

  7. #56
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    Quote Originally Posted by Injuneer View Post
    Thanks for the positive feedback. Funny thing is, these issues are seldom the same, and every time I work on a new problem, like this one, I learn something new - win-win situation. In this case it has me thinking about the fact there are two sources each of battery 12V, switched 12V, and grounds. How is the PCM divided internally to utilize the dual circuits. Are there two “halves” to the controls?

    And, the problem showed up in a scan of just a few seconds of cranking a non-starting engine. Never underestimate the power of a data log. Amazing what can be lurking in there.
    Yes Sir, I think you are correct about the two halves in the early PCM's. I know a tuner who is pretty damned sharp who told me the LT1 PCM's are dinosaurs compared to the newer ones. When I was looking into some reading material to help me understand what he meant, I ran across this article which says alot. In the second paragraph it does indeed say that the early OBD1 PCM did have two processors referred to as Event and Time. See the link;
    http://www.superchevy.com/how-to/0704gm-factory-pcms
    '97 SS SLP,T56, Spec stage 2+ clutch,385 stroker,AFR210,XFI292,Moser 12 bolt eaton posi 4.10's. NO traction til top of 3rd gear.
    '57 Chevy 3100 p/u LT1/T56
    Wife's '94 Z28 has been sold.

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