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Hello all, I have a 2007 GXP and am suffering from a very obnoxious electrical problem, one that caused me to garage the car for a year, up until about 2 weeks ago.

Im on my 3rd alternator now, and have checked the battery, all grounds, the internals of the fuse box, B+ wiring, and the L and F circuits to the PCM.

Upon installation (or reinstallation, oddly) of the alt, HPT will read appropriate F parameters and output voltage is where it should be. However, the L reading stays around 99%. After several restarts, the F holds at 0% and the L stays at 99%.

I checked for shorts in the harness across the PCM connectors and found nothing. On running the car with the harness d/c'd, I did get a reading of over 10v at the L connector.

Ive exhausted all other options at this point. Could my PCM be faulty and frying my alt? Or is there another direction I should go? Is the L circuit voltage controllabe via tuning?

This is incredibly frustrating.
 

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I would help, but not sure what L and F circuits are! Sorry....
 
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What kind of alternators are you using? Any other mods (stereo, etc.) related to the electrical system?
 

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The OEM Acdelco 145amp alt. I have the 8" Monsoon but nothing over the top.

At this point (and Ill confirm this tomorrow), Im thinking my battery was damaged and has a cracked plate or something internally, creating high internal resistance that is frying the alts.
 

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The OEM Acdelco 145amp alt. I have the 8" Monsoon but nothing over the top.

At this point (and Ill confirm this tomorrow), Im thinking my battery was damaged and has a cracked plate or something internally, creating high internal resistance that is frying the alts.
I would bet that you are right. Battery damage, and sometimes even running an alternator without a battery can wreck an alternator.
 

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That is crazy - never heard of it. Please keep us updated on your findings.
 

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New battery is in and new alt is in the mail. I tossed an amp probe on the battery cables and at idle, it never dropped below 20A.

That being said, Im quite concerned about the reference voltage. With the alt harness disconnected, the alt turn on circuit is at 11v. Im going to toss in my old ECM and see what I get. If its between 4.5v and 5.5v then I know my ECM is bad.

Otherwise it has to be a short. And thats just going to be a joy to find.
 
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