dmeeker074

Hi there
Im new here. i have recently acquired a 2001 A4 quattro 2.8lt
after i started driving it i noticed the on board voltmeter fluctuating between 10 and 12 volts. tested the voltage at the positive cable with car running got around 11.5 volts ( to me this indicates bad alt). so I went through the hell that is changing the alternator. immediately upon testing the new alt in the car the on board would go between about 10 and buried below 8 (uh oh) so today did some wheel bearings went to start the car and the battery was dead (this is the first dead battery so far) multimeter on the dead battery reads 4.5ish v jump start car meter reads 13.5ish for about a min then it begins to climb anywhere between 16.5 and 19v now this is where it stays (new alt is a bosch unit from a reputable parts store) once the voltage passes 16v i start to lose electronics in the car (gauges stop working tranny goes into limp mode)

So the questuion is any idea what cn cause this i suspect a bad cell in the battery a ground or bad alt
anyone ever run into this before?

4Driver4

Where did the alternator come from? Autozone? Sounds DOA to me.

dmeeker074

No it came from a local indie parts store, I learned my autozone lesson a long time ago

turbo510

Now that is one long sentence! FYI, never let the system voltage get above 15 Volts for long, if you can help it. While properly-designed control modules, radios, and instrument clusters should have over-voltage protection, or voltage regulators built-in, things like incandescent lights won't last long. I would figure that the regulator in your "new" alternator is bad. Output voltage is determined by the field current, which the brushes conduct to the slip rings. Evidently the regulator is defective and supplying way too much field current.