I have a 98 audi 2.8L Quattra that struggles with accessorizes on.

I recently replaced the alternator with a rebuilt one due to it was beginning to fail and not maintain a full charge any more. It was the original alternator from the car and had over 320,000 k on it.

The first alternator was a match right down to the t of my old one and it would not maintain a stable 14 -13.5 volt charge on idle speed under 1000 rpms would always drop down to battery voltage 12v. SO i had it replaced with another rebuilt one. The new one was the same model and make yet again but i noticed it had about 13 capacitors in it when i replaced the half worn out regulator it had on it compared to the other which had only 6-8.

Now the new one maintains a good charge provided i don't have any accessorizes on even the regular running lights seems to drop the gauge noticeably. The ac/heater will drop it to bellow 12 volts when at idle.

Now i have checked a number of things all listed bellow:
Belt - New OK, Tight
Pulleys - All move freely no wobble
Wires and harnesses - All OK, Tight
Fuses - all OK
Fuel system - All OK no leaks, *thinking i may replace fuel filter is over 1.5 years old*
Air intake - all clean no blocks
Vacuum Lines - Replaced all old and worn out lines, No Leaks.
Codes - None
Dash lights - Service oil will not go out even after a reset and fresh oil change.

Not sure where else to look. the only modifications i put on the car is an after market stereo and a trailer hitch and wire kit. i have recently re taped and checked all these connections and all were OK. I am not using a high tech sound system its just a base pioneer stereo and a couple speakers which have been in the car well over 2 years without an issue.

 

I did a bit of testing with my ac. the alternator is infact not charging to spec. the extra capacitors in the alternator is whats running my car cause when i drain the power with my ac system the voltage stays the same till i rev my engine.

 

That's the risk you run with rebuilt alternators. Gonna have to exchange it again.

 

Yea when i bought it i thought i was buying a straight up new one and was a bit surprised when i found that it was rebuilt and the MTL did not specify that it was a rebuilt one. think ill be sending this one back and try to find a brand new never been used one.