1994 Chevy Beretta car keeps 'eating' alternators

DXECHK

MEMBER
1994 CHEVROLET BERETTA

Electrical problem
1994 Chevy Beretta 6 cyl Front Wheel Drive 195, 00 miles

first of, bought the car in 08, I know from previous owner, that the engine has been replaced before he bought it. The 'mileage' is body only, actual engine mileage is about 110K. I've 'gone through' 7 alternators on this car since I've gotten it. All of them have been just typical re-manufactured ones. We're in the process of tracing wires now to see if we can find any broken or damaged ones that may be causing the problem. Car will run 'fine' for anywhere from 2 days to 8 months is the longest it's run well for me. The battery was brand new as of mid April. The weird thing is, when car is running 'right', the battery gauge reads 18volts, but battery is only actually pushing just under 14. When the battery gauge READS 14, the car is dying on me. Any suggestions as to what to look for, or what to check? We're not sure where else to go. It went to an Auto shop, and did an electrical system check - but they claim they found nothing, except the battery was sitting wrong. They turned it, and strapped it down, and said they got a 100amp reading off the alternator, but less than 2 days later, car was dead again, and alternator was fried. Any ideas or suggestions would be greatly appreciated.

8 Replies

CARADIODOC

MECHANIC
33,742 POSTS

Hi dxechk. Welcome to the forum. There's no way to sugar-coat it, but GM went from the second best generator in the world to the worst pile starting in 1987. Due to its design, it is common to go through four to six in the life of the car. Eight is probably pushing a new record.

The single biggest thing the repair world is finding to make them last longer is to replace the perfectly good battery at the same time as a new alternator is installed. The reason for this appears to be due to the built-in voltage regulator switching the field current rapidly on and off. That creates voltage spikes that the battery will absorb and dampen. As the battery ages, its "internal resistance" goes up which reduces its ability to dampen those spikes. Voltage spikes can confuse the many computers on the car and can damage the voltage regulator and the diodes in the generator.

An important clue to the cause of all these failures would be to disassemble the generator and figure out which part failed. Unfortunately, the way they are assembled, taking one apart is not real easy, and it is common to damage the diode block in doing so. A lot of tests could be performed on the older design, but no tests can be done on this newer one.

Since you already installed a new battery recently, look very closely at the large wire bolted to the back of the generator. That's the wire that sends the output current, spikes and all, to the battery. Excessive resistance in the form of broken strands of wire or corrosion at the connections will allow the harmful voltage spikes to have a bigger affect. Also check the cables at the battery to be sure they are clean and shiny.

Consider buying a remanufactured generator with a lifetime warranty. For the third one my friend put in his Malibu, he found one for considerably lower cost than one with only a one-year warranty from a different parts store. I realize that won't eliminate the chances of it letting you sit on a Saturday night, but east it will take the sting out of the cost.

Caradiodoc

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Sunday, April 25th, 2010 AT 8:02 PM

DXECHK

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Appreciate you getting back to me. Forgot to mention that upon actually getting the new battery, the car had just had an alternator replaced about 3 days before, I believe. And also, the day AFTER getting hte new battery, that alt that had just been replaced fried out as well. We disconnect the battery every time we put another alternator in. Every alt that has been put in so far (by us) have been free replacements through a life-time warranty via Autozone. This last one put in is from another automotive store that my uncle deals with (he was the last one to attempt to look the car over. This one is another facotry 'rebuild' and also has a year warranty on it. My husband actually took this last one apart (not the diodes), and when he looked in it, noticed actual 'burn marks' from where it fried out. He also says that he thinks the nut inside it wasn't properly tightened, I think is what he said. The problem, whatever it is, is getting progressively worse. This is the 4th alternator since mid Feb THIS YEAR. And most of them don't last for more than a week. We've checked the battery cables, they're good it seems, my husband has a volt meter, so he is able to check currents and whatever else. As of last yesterday, when I wrote in the first time, he was in the process of stripping all the tape, and everything else, around the alternator to check for any breaks or burns, or anything else, and so far nothing.

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Monday, April 26th, 2010 AT 11:46 AM

CARADIODOC

MECHANIC
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Boy, this is unusual. Voltage spikes or excessively high current are the only things that should be causing this problem so frequently. AC generators, by their very nature, are self current-limiting. They simply will not produce more current than the diodes are capable of handling.

The internal voltage regulator, like any electronic circuitry, is affected by heat. Is your generator sitting close to the radiator? If so, could there be a heat shield missing?

I'm going to ask a local rebuilder if he has any idea what some common problems are to look for. I'll holler back if I learn something valuable.

Caradiodoc

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Monday, April 26th, 2010 AT 12:48 PM

DXECHK

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No, the alternator is near the firewall on the passenger side, Radiator is about 1.5 feet to the front (like most cars LOL), only thing near it that's related to the radiator is just the reservoir for the coolant. Believe me, you are NOT the only one 'stumped' by this.

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Monday, April 26th, 2010 AT 4:46 PM

DXECHK

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Wanted to give y'all a heads up. Husband was checkin out the wiring again tonight, and was lookin down by the starter, and found a completely fried wired that had been spilced to the starter from the alternator. (pic) Cut it off, and rewired it. Also found ANOTHER wire near the alternator that was broken, and pretty much held together by about 3-4 lines of the wire. Fixed that too. He;s thinking that the broken wire up top was for the actual gauge though. Still need to replace this last alt because it did fry up on saturday. We shall see after we put the next one it how it goes.