Shop Audi Alternators

I recently purchased a 1990 Audi 100 for a work car. 2 days later, whenever ANY electrical in the car is used, the battery drains a little. When the heat, wipers, lights, whatever it may be, is shut off, the battery meter rises back to its standard ( 13 volts) while idling. Needless to say, it makes night driving impossible because LEAVING the lights on kills it. I think its a short somewhere. The fuses seem good. I'm really bad with electrical. Any help would be greatly appreciated!

If you only see 13v at battery with engine running the alternator can't keep up. Loose belt or perhaps a partially bad diode trio or voltage regulator which should both come with a replacement alternator,

T

Thanks alot for your input! I may have misspoke though. Its actually idling close 14+ it seems and driving at 12+ . You're probably still right about the alternator though. Makes sense, especially since I can't seem to find a short. I just hate to replace the alternator since I just bought it for 1g. If that info changes your opinion or you have any other suggesstions, your input would be greatly appreciated!

If you need or want to be very cost efficient there are ways. The heart of the whole deal is the battery. If it's real weak the alternators job can be compremised or work to hard and damage it. Generally if the battery has enough umph to start the car it has enough to allow the alternator to charge the battery and run the assories.

It's a bit odd that the voltage drops when driving along?? The alternator can put out about it's max amps at perhaps 1500 to 1800 RPM. The fuel pump would be using more power driving along just because you are using more fuel when moving than just idling so that could account for some draw.

If the belt it tight enough the odds are the whole problem is withing the alternator from what I see. Most have the voltage regulator inside them - don't know for this one. It's behavior is more like that of one of the diodes that come in a trio (three) being bad and it just doesn't put out the amps to cover much of anything and that won't work for long. Most of the time it would not charge at all and you wouldn't have time to discuss it.

If you find this alternator to be very expensive and it could be the choices are: A good used one if that's available to you. Repair this one yourself if you feel you can handle that. That does take some finesse to reassemble the housing. I'll just plain say the odds are just the diodes would fix this and you could price them out.

There is always some chance of failure or incorrect diag for the fix for this. If you just hooked up jumpers from a donor car with that engine off and your readings behave then I would blame the battery or possibly connections in your car.

Voltage should be: Engine off ~12.2v. Engine running at idle should run up to 13.8 to 14.2 (about) and may drop some with assories on but would go back to about that with a raised idle. If you ever notice voltage go above roughly 14.6 the regulator is a problem and that will burn out bulbs and cause problem with electronic throughout the vehicle.

You don't really have a choice but to do something with this,

T

I want to say thx again for your input on this. So here's what my genius brother came up with. We hosed the alternator down with WD-40 and it ran good for a few hours with the lights on and no significant draw on the battery. We turned everything on and it ran right about 12v for basically 6-8 hours with heat and lights and everything. Then on my way home from work tonight(with jumpstarter handy, mind you) I got about half way home in the dark with the lights and heat on and it started killing the battery again. First the lights dimmed, heater dies, lights go to black, and i have to pull it off the road. I spray that thing down with WD-40 again, jump it and it gets me another 3 miles running at 12v, no problems, UNTIL I hit the brakes pulling into my drive and it juices down under 10v. Being Christmas, I'm trying not to absorb unnecesary expenses which is unfortunately what happens EVERY time I take it to any shop around here. I'm pretty sure after doing some research i can change the alternator myself if thats really the problem. Gonna get the Batt. and alt. tested tomorrow at Auto zone. Any thoughts, comments or suggestions would be greatly appreciated again!!!

This running at 12v only is never going to cut it. This is almost certainly an alternator problem as described in the second post on this thread.

The WD-40 thing would only cause problems now. It will probably collect dirt and make fixing that alternator impractical. The testing should prove that the alternator can't do its job and that should end the chase,

T

Hi, I am starting to tinker around with a 2001 Audi A4 Q 2.8L. I am really not an experienced with cars, but am mechanically able. Anyway, it appears that I need to replace an alternator. The battery measure 12.5V no load and then 11.4V when the car is running. I just have a simple question: am I on the right path with the alternator or is there something else I should check before investing the time and money into that job? The above battery test is pretty much all I have done diagnostically.

Thank you.

You're probably on the right track as long as all the fuses and fusible links are good.

I own a 1988 Audi 200 and recently i forgot to turn the lights off so the battery died. I tried to re-charge it by driving it for a while on the highway, the battery held the charge well enough to keep me on the road driving but when i tried to start it up again later it wouldn't start because the battery was dead. The alternator is ok because it is keeping a charge while i drive it but why isn't the battery actually charging up and holding a charge? any help with this matter would be greatly appreciated.

You need to have the battery tested. It's likely bad. And for the future, don't ever use the alternator to charge a completely dead battery. They are not made to do that. They are only designed to maintain a battery, not charge it from dead. I have seen many a good alternator burned out by doing that.

I have an early 90's (93 maybe) Audi 100 and I am wondering if someone can help me figure out what is wrong with the battery. I was driving yesterday and the battery light came on, so I got the where I was going and shut it off. Later, I started it and it started up fine, the battery level was low, but not that low, so I start driving and after a few miles the same thing happens. I let the car sit for about an hour, start it up and again it seems a little low, but not bad, I drive it around the block again and it drains it again. So I leave it sit overnight, started it this morning, and it seems charged again, start driving and it slowly drains again. It almost seems like there is something that is just draining the battery faster that the alternator can charge it, but when the car is off, it still charges it. Antone have any ideas? Any help would be appreciated more than you can imagine.

Check the alternator belt and tension. Could be slipping at higher rpms. Check alternator output. May not be enough to handle accessories.

The tension makes sense. It does seem looser than the other belts. How can I go about tightening it?

If you've inspected the belt and appears to be okay (not shiny from slipping, no cracks), you should be able to take a close look at the alternator assembly and tell how to tighten the belt. Most cars, you can loosen the two bolts that hold the alternator tight and using a pry-bar, move the alternator until the belt is tight, then re-tighten the mount bolts. Others have an actual adjusting bolt that you turn after loosening the alternator. Just have to look.