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90 Audi 100. Battery, Alt., fuses...help
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hagert
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Nov 27, 2007, 7:27 PM
Post #1 of 6
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90 Audi 100. Battery, Alt., fuses...help
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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!
(This post was edited by hagert on Nov 27, 2007, 7:28 PM)
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Nov 28, 2007, 5:32 AM
Post #2 of 6
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Re: 90 Audi 100. Battery, Alt., fuses...help
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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
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hagert
New User
Nov 28, 2007, 7:27 AM
Post #3 of 6
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Re: 90 Audi 100. Battery, Alt., fuses...help
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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!
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Nov 28, 2007, 8:46 AM
Post #4 of 6
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Re: 90 Audi 100. Battery, Alt., fuses...help
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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
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hagert
New User
Dec 3, 2007, 8:55 PM
Post #5 of 6
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Re: 90 Audi 100. Battery, Alt., fuses...help
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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!!!
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Tom Greenleaf
Ultimate Carjunky
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Dec 4, 2007, 3:12 AM
Post #6 of 6
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Re: 90 Audi 100. Battery, Alt., fuses...help
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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
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