stumped - erratic charging circuit - Page 2 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 08-19-2004, 12:33 AM   #11
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Default one more thing

I was just doing some reading at alternatorparts.com and the self-exciting one-wire voltage regulator alternator looks attractive. I would not need to worry about why my alternator "L" terminal is receiving intermittent voltage. Any thoughts on this?

Thanks
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Old 08-20-2004, 02:24 PM   #12
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Have you thought about stringing a new wire from the PCM to the alternator? Have you tested the voltage at the PCM while driving around? How about the voltage from the PCM at the alternator?
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Old 08-22-2004, 02:25 AM   #13
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Default erratic charging

Lately I have been driving around with my digital VOM monitoring the signal on the PCM connector. Readings act the same in both locations.

The problem has been present alot lately and the VOM shows 0Vdc (meter shows 0.0V) on output OR it also indicates an open occasionally (meter shows - 0.0V). When it begins or is "trying to work" the meter shows erratic voltage from a couple volts, then up to about 9-10V, and then if it steadys out to around 11 or higher it will begin charging again.

It does not seem to be thermal related, either.
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Old 08-22-2004, 02:59 AM   #14
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So the voltage is 0.0 at the PCM? Have you tried disconnecting the wire from the PCM and applying 12V+ back to the alternator?
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Old 08-23-2004, 12:36 AM   #15
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Default .

Yes - 0V or erratic low voltage was present directly out of the PCM.

I have disconnected the alternator connector and directly applied 12V to the alternator "L" terminal using another alternator plug and a jumper wire to the battery. I did not know if this was a good idea but it did make the alternator charge. However, this only worked a few times for some reason.
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Old 08-23-2004, 02:40 PM   #16
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I would be interested in seeing if the jumper wire made the alternator charge the correct voltage... It'* hard to blame the PCM, but it sure looks like the culprit here.
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Old 08-23-2004, 08:23 PM   #17
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Default

You may have tried this already. run a jumper from the case of the alt. to a known good ground. The reason I say this is the quickest way to open up rectifiers is to lift the ground. {you stated a previous alt. failed a diode test}. If Im not mistaken, these things ground at the case {rectifier bridge and rotor}, then through bolts, block, and engine Ground strap.

You can check resistance from case to neg. battery while the thing is acting up and mabe see an increase in resistance.

Hope this helps... Good luck.......
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Old 08-23-2004, 10:21 PM   #18
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Smallblock, that was one of the many tests that I ran on mine when I had my problems, with no improvement, but still a good suggestion for Bonny95 . The way these things act, I think the the voltage regulators cannot keep up with the fluctuating inputs the L connector throw at it. The regulator responds to the input of the L terminal to determine the output of the alternator. The PCM is what sends this signal to the alternator via the L terminal, as the PCM monitors power demands. I kinda think their is a bad design in these PCM'* that allows this to occur. Didnt I see in a post in the recent past about an upgrade on the chipsets in the PCM'*, and has anyone noticed a difference that has installed one?
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Old 08-24-2004, 12:07 AM   #19
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So the "L" terminal expects fluctuating voltage? Does this mean the PCM is not seeing the right voltage or miscalculating power demand?
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Old 08-24-2004, 12:17 AM   #20
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Default .

Today I applied 12V from cig lighter to the PCM connector of the wire that goes to the "L" terminal and the alternator will charge. I only did this briefly as it is probably not a wise or safe thing to do, correct? I wondered if I fried alternator #2 doing this. Is this possible?

I will probably be installing a self-exciting alternator or adding this type of regulator to my existing alternator. I am just trying to decide if I should spend $130 on the new alt or add the $44 reg to my alt.

In answer to the suggestion, I have run a dedicated ground on the alternator with no luck.

Thanks for all the help and ideas...I appreciate it.
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