My alternator went out a few weeks ago on a long trip home from the ocean. I was able to make it home before the car died sitting in my driveway. I replaced the alternator with a rebuilt one from NAPA. Ever since then the voltage in my car has been all over the place while driving. When I come to an idle the voltage drops to around 8 volts(this is often with AC on). I realize at idle that the voltage will drop. However when I speed back up(around highway speed) the voltage will stay around 8 volts for a minute until all the sudden the needle goes back up to around 13/14 volts within a second. I originally thoght it could have been the new alternator not working properly until the other day when i was sitting still and the car was at around 13/14 volts and when I sped up it shot up to above 18 volts. Any thoughts on what could be causing my voltage to jump all over the place?! I realize different speeds will cause voltage to change but I’ve had this car for about 3 years and have never seen it do anything like this.
I guess I should mention it is a 1993 Chevy Beretta 3.1 V-6
My initial thought was that the belt wasn’t tight enough, but that wouldn’t explain the high voltage. But I’d go back and check to make sure the belt is tight and that the ground connection is good.
If it was a rebuilt unit, it could just be a bad one. I had a similar problem and had to go through three units before I got a decent one. If it’s under warranty, take it back.
That was one of my questions…I’m not sure if my regulator is in the alternator or not. I know in older cars that it’s commonly mounted on the firewall. I checked online and found that I can purchase a new regulator…that would make me think it is separate from the alternator but I may be wrong.
The regulator is built into the alternator. You can buy a regulator separately, but the new one would be replacing the one inside the alternator.
My thought is the rebuild is bad. Happens every now and then. The only other possibility I can see is a bad gauge. Easily verified by hooking up a voltmeter while the car is having the problem.
I recommend you get it fixed soon. If it is really putting out 18V you can damage various electronics in the car including the powertrain computer.
On some late-model cars the regulator function is handled by the ECU (“computer”). On those cars, there is not a separate regulator available.
On modern cars in general, the regulator is inside the alternator. I’m pretty sure it’s been a number of years since anyone has built a car with an external regulator.
Your description of the symptoms clearly points to a regulator malfunction, which means you got a faulty alternator. Get a replacemtent under warranty.
As zwede mentioned, that high voltage can do–and perhaps has already done–some damage. If you don’t want the hassle of dealing with a fried ECU, replace the alternator yesterday.