I think what it happening is the PCM sees such a fluctuation in voltage, the voltage regulator is getting mixed signals from (L terminal) and could possibly start overheating the regulator, just a theory. I purchased a new voltage regulator for an alternator that was a "good" typical parts chain store brand, that started to dip down in voltages after two months. I will install and see if it goes well for a little bit. The regulators always worked good for the first few minutes after startup, then started going all over the place.

The voltage regulator should supply field current (internally) depending on electrical loading on system. During heavy electrical load maximum field is applied, conversely during light electrical loading minimum field current applied or possibly none. (alternator windmilling, battery carrying electrical loads. This scenario may only last for very short durations) That "L" signal between PCM & alternator may be pulse width or pulsed, not entirely sure.

About a year ago I had a similar problem with my 95 SE. Erratic output from the alternator, it would output less than 10V at a stop or very slow speeds. This was an intermittent problem, some days it was fine other days it would act up.

One morning I started the car and saw that the voltmeter was all over the place, 8V then 14V then 10V....ect. I removed the alternator and had it tested, it was fine. The battery was new, so new it was fine. I checked the wiring at the battery, alternator ect., everything looked fine. My neighbor stopped over and suggested I take out the ignition control module, clean it and the mounting plate surface. So I did it. Since that day I have had no erratic charging issues. I am not sure how I fixed the problem, because I cleaned every wiring connection I could find. Battery, alternator, ICM, starter ect. I also used dielectric grease on everything.

Well , im stumped...... I hope you get to the bottom of this thing, as i know the headaches ... It may very well be the pcm. The only other thing that comes to mind, and this is a long shot I know, is a polarity reversal. Its not likely on a neg. grd. system, but may be worth a check....... good luck.....

Update:
I was lucky enough to find a PCM from the junkyard for $45. I ohmed out some of the main power distribution circuits and I am ready to take a guess and change the PCM.

My question is - do I have to find a Tech1 or similar scan tool in order to change out the PCM? The junkyard PCM was installed and the car will not start. I guess my book is correct - I need a scanner, correct?

What kind of car did the PCM come from? Did it come from a 1995 supercharged Bonneville?

The computer is from a 1995 supercharged Buick.

That'* pretty close, but I would still swap the PROM from your computer and put it in the replacement computer.

fuseable link replace wire from alt to battery

I was just going to post on this topic but since this issue is already at the top I will not post another thread.

For me the voltage was all over the place. It started 6 moths ago and it has done it every day I have driven the car since then. This weekend the alternator was not charging at all and the voltage was brought down far enough that the car would not run. I chaged the battery, which got the car home, but I was still seeing consistent very low voltage with no fluxuations.

I had the alternator and battery tested, both tested fine, so I was stumped. It appeared the wire from the alternator going into the battery connection was pulled out some and I guessed it ws not making good contact. I cut the wire and installed a new end and connected it directly to the battery and finally no more swings in voltage. I have driven the car about 25 miles and the voltage has sat at a steady 14 where as before I couldn't drive the car 5 miles without seeing the gauge all over the place.

I did not replace the entire wire as sugested in the post above and I never gave it a thought about being a fusible link but that certainly could also be the problem. All I know is a poor connection from the alternator to the battery was the cause of all my headaches. I will keep you posted if it returns.