I have a 1998 Bonneville that has a power problem
When the engine is running at idle The voltage guage goes down to a lower voltage for a bit then returns to around normal, at the same time my lights dim and if the blower is running it slows down a bit then goes back to normal. I have replaced both the alternator and the battery. I have cleaned and checked all the battery cables and connections. The ground to the body from the battery, the back of the alternator, the wire going to the fuse/relay center, the negative battery wire to the engine block. All of these connections are clean and tight, and I still have the same problem. While traveling to and from work on the highway my volt guage stays around 14 and steady, when pulling up to a stop light or sign I get the fluctuations noticed more when adding to the draw by stepping on the brake pedal, but the guage always trys to make it back to normal.

This problem has plagued me for about 3 months now.

I would appreciate anyone'* input if they have come across this before and could help me with a solution, short of relacing all the wiring.

Thanks

Tell us what brand/type of battery and alternator you have, and also what RPM'* the engine is at when this happens. Also the age and condition of your accessory belt, and whether the problem seems to be more prevalant during wet or cold weather.

Moving to Electrical.

Not sure of the brand of battery, got it at a Meijers store: has 940 Amps 800CCA
Alternator is a direct replacement of the OEM alternator 140A alternator
Serpentine belt could use a replacement when the funds are available, but doesnt slip yet
The engine idles around 700 to 800 rpm in drive, about 1000 or 1100 rpm in park
Thje weather doesnt seem to affect the readings on the guage, it has done it both in warm and cold weather. This vehicle has had a problem like this for a while, and after replacing the battery and alternator I still have the same issue. It gets annoying after working on it and not solving the problem. The car seems to run and function normally but still is annoying.

Mine does the same thing, and after searching and reading here the only answer I could find was from GM saying it was our own fault. The electrical system doesn't like aftermarket stereos (GM said it, not me) and such as that.

I have the 140 Amp Alt, and it never quite makes it to the red, but she can dip at times. I have found, tho, that by keeping the fan on 3, or next to last, or whatever and making a fairly long constant speed run, it seems to drop a lot less after that.

I'm hoping to upgrade to a 200 amp alt soon to stop it altogether, but for now I just deal.

There was an article posted here, though, about upgrading the alternator wires to "monster cable" to provide less resistance.

Ok, the 140 is great. Shouldn't (but could be) a problem out of the box.
The alternator pulley is your smallest diameter. Belt slip could be a problem, although it usually manifests itself at the higher RPM'*, not the lower.

The problem only happens at idle in gear? Never at the higher rpm in park?

Yes only at lower rpm'*.

If I rev it up to around 1000 or 1100 rpm'* the volt guage seems to stay around 13 to 14 volts, but you wouldnt want your car to idle at that speed because in park it would be racing. It seems to me either its a module problem of some kind or maybe a grounding issue, but I have checked all the grounds I can find. I know on older vehicles there was a ground strap from the back of the engine to the firewall, but I cant seem to find it on my car. Thats about the only ground I cant find. I had it checked at my mechanic'* shop yesterday with the car stopped and also running, and according to his tester with everything on (blower on high, high beams on, windshield wipers on, car in drive) it still indicated that the alternator was charing the battery at about 13.9 volts, from 14.6 volts when everything was off and the car rpm'* were at cruising speed.

well maybe your gague is just off then...13.9 with all the accessories on is pretty good

The guage is part of the problem...............................



The problem is:

the lights are dimming down and returning to normal brightness for no reason

the blower motor slows down and returns back to normal for no reason

the cars acts as if it is losing power then all the sudden it returns only to lose power again, like an intermittent connection or a power module or something freaking out.

NOT THE GUAGE

correcting the last reply on the first line





The guage IS NOT part of the problem

Tossing a couple suggestions out.

Have you checked the ground buss by the driverside floor? Possibly got water, corroded at one time and maybd due to foot placement it starts acting up. You get nervous shift position and it straightens out.

I know..it'* a stretch, but another possiblility to check out.