Repeated alternator failures - help with diagnostics

[scenturion]

Hello folks,
A couple of weeks ago, the alternator in my Coupe failed.
The voltage dropped to ~11-12V and the battery light in the cluster was dimly lit.
I drove the car to OReilly Auto, and they used their diagnostics tool to say that the alternator voltage regulator was bad. Of course, I don't know if thats actually true, but they said the battery tested fine.
I ordered a Bosch remanufactured alternator and installed it. The voltage went back up to 14V, but after ~165 miles, the alternator failed again with the same symptoms.
I tried swapping a known good battery out for the one in the car, but the voltage still would not get any higher than 12.5V.
I ordered yet another Bosch reman alternator, but today it arrived with mechanical damage so I was unable to install it.
However, I swapped the voltage regulator from the recently-arrived damaged alternator into the existing one, but it had no effect - same symptoms.

Is it common for a remanufactured alternator to fail after such a short while?
I was surprised it was something other than the voltage regulator that failed (or that the regulator from the damaged alternator was DOA)

I noticed on the wiring diagram that the D+ terminal on the alternator connects to the TCS and instrument cluster via data bus.
Could something on that data wire be killing the alternator or is it more likely that the failures are coincidental?

Wiring diagrams here.

It's also somewhat strange that when the ignition is in accessory position (without the motor running), the battery light is at maximum brightness.
When the motor is running and the voltage is the same, the battery light is noticeably dimmer and flickers slightly brighter and slightly dimmer constantly.

Picture here - battery light is brighter than appears in the right image because of the brightness correction of the camera. In daylight its so dim as to be unnoticeable.

I am out of town from Friday to Sunday and am supposed to drive the car down to Dorkfest next weekend...
Thanks for any advice

[jclausen]

At this point I would have a shop look into it don't want to fry any thing because of the faulty alternator.

[BimmerBreaker]

I would have at that point been checking engine grounds and battery connections, then found a known good (used) alternator to swap in. Certainly unusual to receive so many bad parts in a row though not entirely unheard of, but it does seem like something else is going on. Curious what the shop reports as being the issue

[scenturion]

I checked and cleaned the ground straps and connections in the engine bay. No dice.
I'm not sure what a shop could do that I can't. Maybe my view of shops is fairly dim, but I would expect them to just try replacing the alternator again.

[z3forlife]

I would swap the reman unit out under part warranty and see what happens. Assuming the diagnosis of the original unit was correct and the fact replacement of that part on the new failed unit didn't resolve the issue points to different failures perhaps. Since the 2nd replacement was damaged on arrival you don't know if it's good or not

[scenturion]

The replacement reman unit will arrive tomorrow. FCP Euro has been incredibly helpful and has earned a customer for life.

[BruceWarne]

It's not something dumb like a slipping belt perhaps?

[Adker]

I noticed on the wiring diagram that the D+ terminal on the alternator connects to the TCS and instrument cluster via data bus.
Could something on that data wire be killing the alternator or is it more likely that the failures are coincidental?

There is one wire coming from the dash alt light over to the alt. With the alt not running, the D+ terminal is close to ground potential and the light turns on. When the alt is running, the D+ terminal has the same voltage at the B+ terminal and the light turns off. If the light is slightly on, the alt D+ terminal is at a voltage lower then the B+.

I would measure the voltage at the B+ terminal and if it is low I would disconnect the wire and see if the voltage goes up while it is running. If it does, then maybe the TCS or data bus connection are pulling the voltage down. Some car alarms will clamp the D+ to ground when armed to keep the battery from charging.

Do you have a large after market audio amp? They are know for burning up alts.

[Cremaster]

Just wanted to respond. When I saw "OReilly Auto" I had to remember my daughters experience with OReilly. She had 2 alternators replaced on her car with in 2 weeks. You got to remember that OReilly, Advanced, and the rest of those discount sites sell by volume. They would be ok with selling 1000 alternators purchased on the cheap from suppliers that want to sell 1000s of alternators at once and maximize their profits by having an "acceptable" return rate of say 3 in 100. They make the extra $$ and don't have to check each solder joint, or each housing, they just have to put them together as fast as they can and refund $$ on the ones that are defective. The end user is the one that has to replace the new part that broke not the guy that made it. Not a big deal if it is an easily replaced part but an alternator is not so easy to replace. You don't see a lot of mechanics using Pep Boys, ORiely and such for parts like these, they pay higher prices because they want to purchase quality parts. It pays them not to have to do the job twice or thrice.

[scenturion]

Update: I installed the 3rd alternator, and the voltage regulator was bad out of the box. It was putting out ~15.8V.
Not to be dissuaded, I swapped the voltage regulator from alternator 1 (the dead one on the car) into alternator 3 and it seemed to work well.
A friend borrowed the car and put 150 miles on it over the weekend and so far so good.
I am still not clear what the original failure mode was - I tried checking for AC current at the battery but it was only .05V, so not what I would have expected for a failed diode pack.

I noticed on the wiring diagram that the D+ terminal on the alternator connects to the TCS and instrument cluster via data bus.
Could something on that data wire be killing the alternator or is it more likely that the failures are coincidental?

There is one wire coming from the dash alt light over to the alt. With the alt not running, the D+ terminal is close to ground potential and the light turns on. When the alt is running, the D+ terminal has the same voltage at the B+ terminal and the light turns off. If the light is slightly on, the alt D+ terminal is at a voltage lower then the B+.

I would measure the voltage at the B+ terminal and if it is low I would disconnect the wire and see if the voltage goes up while it is running. If it does, then maybe the TCS or data bus connection are pulling the voltage down. Some car alarms will clamp the D+ to ground when armed to keep the battery from charging.

Do you have a large after market audio amp? They are know for burning up alts.

I'll keep this in mind, I would have liked to do this test. If it happens to die again I'll try pulling the D+ connection off.
I don't have an aftermarket alarm system or amplifier.

Just wanted to respond. When I saw "OReilly Auto" I had to remember my daughters experience with OReilly. She had 2 alternators replaced on her car with in 2 weeks. You got to remember that OReilly, Advanced, and the rest of those discount sites sell by volume. They would be ok with selling 1000 alternators purchased on the cheap from suppliers that want to sell 1000s of alternators at once and maximize their profits by having an "acceptable" return rate of say 3 in 100. They make the extra $$ and don't have to check each solder joint, or each housing, they just have to put them together as fast as they can and refund $$ on the ones that are defective. The end user is the one that has to replace the new part that broke not the guy that made it. Not a big deal if it is an easily replaced part but an alternator is not so easy to replace. You don't see a lot of mechanics using Pep Boys, ORiely and such for parts like these, they pay higher prices because they want to purchase quality parts. It pays them not to have to do the job twice or thrice.

The part didn't some from OReilly's. OReilly doesn't even carry the Z3-style alternator - they cross reference it with the normal E36 alternator.
I ordered the Bosch remanufactured Valeo part from FCP Euro, which I thought was enough of a name brand part that it would work.
The quality and workmanship was all over the board with the three alternators I received. Some had random washers, they had different potting on the voltage regulator, etc etc.
Also, the alternator on the S52 cars is about as easy as it gets in terms of part replacements. No need to get under the car, bolts are easily accessible.

[CMM3]

I had a similar problem, after adding Electric Power steering I went through 3 alternators / V regulators. Finally I purchased a high output alternator from a alternator shop and problem solved. Most of the re-manufactured ones are junk and won't last.

[scenturion]

Was this a local shop? Do you have any recommendations for a buy-it-once alternator?

[scenturion]

Bump to say that I put 1100 miles on the 3rd alternator without issue. I guess I just had a bad run of Bosch reman alternators, though I am not clear on the failure mode of the original and 1st replacement alternator.
I heard rumbling on a Facebook group as to a systematic stator issue with rebuilt alternators. Anyone know anything about it?

[CMM3]

Was this a local shop? Do you have any recommendations for a buy-it-once alternator?

Yes local to me in MA. but they will ship anywhere....Chelmsford Auto Electric 800-649-4448 the part number on my receipt is 8004004J
Ask for Brain and make sure you tell him to build you a 160a a 3000 rpm / 180a a 4000 rpm for your car
It will have heavy duty diodes that will last.

Voltage spikes kill the diodes as well as the Voltage regulators in the stock or cheap re-manufactured units. And they don't always fail completely sometimes going intermittent.

I believe the ones in the above are 50 amp versus 25 amp and there are 6 of them in the alternator rectifier which is different and separate from the voltage regulator.

altenator.png

it will solve your problem for good.

Sorry for the late reply.