Mechanics

REPLACEMENT ALTERNATOR KEEPS FRYING!

2001 Audi A8

Electrical problem
2001 Audi A8 V8 All Wheel Drive Automatic 160000 miles

Thanks for the help!

I have replaced my alternator twice now and get the same results each time.
I believe it has everything to do with the alternator connections.
The original had only B+, and D+ terminals, with ground being the housing attached to the grounded engine.

The replacement has B+, D+, and now a DF terminal which I can find nothing about anywhere on this.
When I measure output at terminal D+ with the engine in idle, I get extremely low voltage measurements. All while B+ shows just under 12.2v (I assume some loss of voltage from starting the engine). There is no wire in the region for this DF terminal.

I am being told to jumper the DF spade terminal to ground, then someone else says to B+, then someones else says to D+, I assume it just didn't need to be connected at all, But with this being the 3rd alternator and still getting low low voltage readouts at terminal D+, I am at an utter loss.
Help please!
Thanks so much
Avatar
Tigercleveland
February 23, 2010.



Hi there,

Thank you for the donation.

The DF terminal is not used see pic for wiring,


http://www.2carpros.com/forum/automotive_pictures/61395_audi_2.jpg



Set up alternator as per pic and report charge rate here.

Mark (mhpautos)

Mhpautos
Feb 23, 2010.
Hi and thanks again so much for the help!

Verified only B+ and D+ connected.
Before I started the engine, battery measures 12.3v, B+ measured 12.3v, D+ measured 0.00v

With engine on in idle, battery measures 11.6v, B+ measures 11.6v, D+ measures 0.92v and very slowly climbing one-hundredth at a time (i.E, .88v to.89v to.90v)

Before this alternator change, there were no cel's or any sign of any other wrongs.
Thanks again!

Tiny
Tigercleveland
Feb 23, 2010.
Is the charge light on? I will have a word to an elect as this is now getting a little out of my field.

Mark

Mhpautos
Feb 23, 2010.
Thanks again!

Yes the charge needed light is on with the car running, according to the manual meaning alternator not supplying enough voltage.

I have run the pull each fuse one at a time and check continuity, etc. Found no shorted circuits

Thanks so much for the help, will donate more$ shortly.

Tiny
Tigercleveland
Feb 23, 2010.
Sorry but more questions for you,

Did you at any time remove the battery terminal with the engine running? Did you unplug any alt wires with the engine running? If so you may have blown a diode in the rectifier in the alternator, I think what you need to do next is prove that the alternator is working by having it tested on a bench charge tester, this will take an auto elect about 5 min to set up and test, knowing that the alt is sound, we can then start looking at the rest of the charging circuit for problems, I don't have a lot of tech info on Audi's to hand so we will do our best.

Mark

Mhpautos
Feb 23, 2010.
Hi and thank you so much again for the help

On this unit, I have not removed any terminal connections or alternator connections, did this unit as textbook as I could honestly. Full deep charge, new unit, etc.
I would be happy to run get it bench tested tomorrow to be certain as well, do most auto stores have the equipment to do this?

One thing odd I did notice on this alt and the previous one starting was (new belt, well seated, tension) a noise from the alternator like it didn't want to turn a small burning smell and then the pulley would start to move quickly and sound fine. On this unit today I installed, the pulley was spinning freely clockwise/ctrclkwse; however once the alternator was connected with B+, D+, as I was seating the belt around it's pulley, the pulley would not spin at all even with a firm turn attempt w/ rubber mech gloves on.
As I started the engine to test the output of it, the noise described above occurred, I thought maybe a 'burn in' is req'd to get it generating voltage and designate it's polarity.
But the primary thing I noticed was that the new alt pulley locked up for sure when I was finished connecting B+ and D+, is that normal? The battery had not yet been connected and it locked regardless.

Thanks again!

Tiny
Tigercleveland
Feb 23, 2010.
Hi there,

The alternator test bench is the domain of the auto electrician, parts store wont have this level of testing, with the lock up noise and smell, all bad signs, this just should not be, the alternator should spin freely and any burning smell is a death sentence for the alternator, you should be able to hook up and start no bedding in nothing. This is all very strange, I feel that with that info your current alt is toast, but you better get it to an auto elect and get it tested, hopefully it was faulty from the start,

Mark (mhpautos)

Mhpautos
Feb 23, 2010.