I have a '99 a4 b5 2.8L with 130k as my daily driver.

So here is my issue: About 6 months ago my alternator took a dump and I replaced it with an advance auto reman. (I know I was asking for trouble).
About 3 months ago the alternator started to charge around 12.5 to 13 volts and not a full 14V. So while at the junkyard on another mission, I saw a passat that was rearended. I snatched the alternator out of it, had it tested, and it came back as good. I swapped it in and had the same exact problem!!!. I find hard to believe that 2 alternators, one salvaged OEM, and one reman. have the same problem.

The problem has gotten worse now. When I start it up, it will charge around +-13v and after about 5 minutes (at idle or while driving) it will dip down to 12v and then lower to around 10 or 11 volts. Thus draining the battery to the point where it doesn't have enough power to turn over to start. It will sometimes spring back to around 13 volts for a min or two but then will drop back down to 12v or less.

I have done some research and heard it could be bad wires from bat to alt, bad ground, bad stator, spun stud on the alt.... I plan to go at it with a multimeter this weekend to try to pin point the problem.

Has anyone had this problem before or does anyone have any words of wisdom?!? I'd like to have somewhere to start.

Thanks!

 

That is very interesting but since you mentioned that you were experiencing the same problem with two separate alternators than I can safely say that the alternator itself is not your problem. I doubt the wiring is shot but you never know. Check your ground for sure. Once you eliminate some of the possibilities I am confident it wont be too difficult to converge on your problem.

On another note.. Did you make sure the alternator from the Passat will work with the Audi? I think it should but you never know. Sometimes the slightest difference will mess things up.

 

How old is your battery? Wouldn't be the first time a bad battery has caused strange issues.

 

Yeah checking ground will be my first course of action. After that I'll just run through everything to try and rule things out. I did make sure the alternators matched before I installed the one from the junkyard so that should not be an issue. I plan to dive into it tonight...

 

It is going on a year old and was only about 6 months old when problems started. I plan to get it tested first to make sure what you're saying is not the case.

Thanks for the input so far!

 

Good luck tonight. Grounds would be an excellent place to start, especially check for corrosion and what-not. Maybe also have some dielectric grease handy to prevent future corrosion?

 

So before digging deep into things I found that when the volt meter falls below 12v, the oil temp gauge rises to around 350 deg simultaneously. While pumping the brakes when the volt meter reads less than 12v, the oil temp needle moves. Also, while raising the windows from the down position the oil temp needle pegs up. Its as though the oil temp gauge is responding to load on the electrical system... which further confuses me. Does anyone have any ideas about this and/or does this point to a possible cause for the issues I have??? Thanks!

 

gdrenn15,

Have you found out the problem yet? I have a similar issue where my alternator appears to be functioning at times and then not others. Specifically, when I start the car, it's @10-11 on the voltmeter. I rev the engine and it goes up to 13/14 like it should and stays there for a while before usually settling on 12/13.

 

I have the same problem you have I replaced my battery and that didn't work I have an Audi A4 2000 2.8

 

Curious about the Passat alternator - was it identical to the one in your car? There are two brands used on the B5, Bosch and Valeo, and each can be either 90A or 120A. You must have the same one that your car came with for it to work right.