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Old 03-24-2008, 04:05 AM   #1
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Default Volt meter problems

I've read several similar posts about erratic volt meter movement. Nobody mentions if and how they solved the problem.

Heres what mine is doing. it fluctuates from the time the engine is running to the time it turns off. when off it reads 12v. when on it jumps constantly from 11.5-15v without holding still. The lights and stereo etc. never dim when the voltage drops. The battery is brand new. I took a reading while this was occuring at the alternator. Used a multimeter with contacts on the positive terminal under the hood and the alternator mounting bolt. This reading was between 14.3-14.9v. I got this same reading on my amplifier terminals. Recently I have been hearing a noise like a worn bearing coming from the engine compartment that sounds off in time to the fluctuations. There still are no visible signs of voltage drop (lights, etc.).

I plan on trying readings on the battery terminals itself, the ground strap, etc. I also will take it up to Checker and have them test it on the car and on the bench.

Has anybody found a solution to this problem before?

Thanks
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Old 03-26-2008, 02:22 AM   #2
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anyone.... anyone?
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Old 03-26-2008, 11:00 AM   #3
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I can't speak for others, but I was waiting for you to provide the additional information on what you found after you did what you said you had planned. Also, what things have you already done to try to fix the problem? Cleaned up any connections; had the alternator tested, etc..
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Old 03-26-2008, 01:36 PM   #4
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sorry - just hoped somebody had already had this issue

I gotta go dig through the storage unit today and find my multimeter

I'm not known for my patience
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Old 03-26-2008, 03:05 PM   #5
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I couldnt find my multimeter but did get readings off of checker'* electrical system tester.

14.3-14.9v at the alt
Test failed due to excess "ripple"

IIRC this means that the diode in the Alt has gone bad and is now essentially charging and discharging the battery. Please correct me if I am wrong.

I checked the terminals under the seat and they look brand new. No corrosion or rust at all.

So it is fairly obvious that the alt is bad - is there a way to repair it? Also I am wondering if my amp setup could have contributed to this as this began happenning a few months after it was installed.

here is how the amp is set up. (I am no electrician)

Positive 8GA fused lead attached to the positive terminal on the under seat fuse box.
Negative 8GA lead attached to the frame ground bolt under the seat along with the grounding "strap" aka big fat cable.
Turn on lead jammed in a fuse providing switched 12v on ON only.

The amp is a rockfor fosgate class AB
It is running at 250 watts RMS at 4ohms


well thats the rundown - thanks for the help
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Old 03-27-2008, 01:13 PM   #6
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are the 99-older bonneville alternators the same as the 2000+? If so i may just pick one up at the junkyard. Yards around here don't have any cars newer than 1999.
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Old 03-29-2008, 11:58 AM   #7
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If you want a quick answer to your question, compare part numbers by doing a lookup for both year Bonneville'* on PartsAmerica.com (Advance Auto Parts online). This will instantly tell you if they are the same or not. I believe they are, but don't quote me.
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