Help with E34 M50 Alternator Diagnosis/Repair

[squirrelhill]

This weekend the alternator on my 1995 e34 525it seemed to have died on me. I was driving on the highway and the dashboard lights all started to illuminate, starting with the ABS light, the speedo and tach needles going dead and culminating with the Trans Prog error message. Luckily, I was able to get the car off of the highway and into a safe parking space on battery power. I jumped the car a couple of times, but it would only run for a few minutes before setting off the light show and then dying out. I had the car flatbedded home. Prior to the alternator giving out, I did notice some engine whine at the beginning of my drive and some pulsating of the dashboard lights.

Once I got the car home, I verified secure connections at the battery terminals and at the back of the alternator (after removing the battery and placing it on a charger). I also verified a good connection for the engine ground wire, which there is, although the cable itself is rather worn and ratty in a couple of places. I am going to replace the engine ground as part of the beginning of this repair.

Of particular note, I am not getting a red battery light on the dashboard when starting the car (KOEO) or when the car is running (for the few minutes before it totally dies).

My initial question -- should I start with replacing the battery light bulb in the instrument cluster, understanding that this acts as an exciter circuit for the alternator, or is the problem more likely with the alternator itself -- VR or bearings? In researching this issue, I seem to recall that a bad VR will cause the battery light not to illuminate and that, in any case, there is also a resistor built into the exciter circuit. I would hate to go through the process of replacing the battery light bulb if the problem is more likely with the alternator itself. Conversely, I would hate to pull the alternator if my first step should be replacing the bulb.

Any thoughts/guidance/experience would be very much appreciated, especially relative to whether I should start with the battery light bulb or move right to diagnosing the alternator.

[MIKYZZ4]

I would initially remove battery, as you have done, slow charge battery overnight on a slow charge, reinstall battery-take a voltage reading across battery terminals,
(12.4~12.7v). Start car, take voltage readings(idle-2000-3000rpm)should vary between(13.5~14.5v).

[bblazen]

I would initially remove battery, as you have done, slow charge battery overnight on a slow charge, reinstall battery-take a voltage reading across battery terminals,
(12.4~12.7v). Start car, take voltage readings(idle-2000-3000rpm)should vary between(13.5~14.5v).

This and while running turn on loads(high beams, HVAC, radio) and check voltage.

Sent from my Nexus 6P using Tapatalk

[ZUUD BYE]

I would initially remove battery, as you have done, slow charge battery overnight on a slow charge, reinstall battery-take a voltage reading across battery terminals,
(12.4~12.7v). Start car, take voltage readings(idle-2000-3000rpm)should vary between(13.5~14.5v).

+1

If alternator is dead, with the car running you will see the battery voltage slowly go down from -12.4~-12.7 VDC on your multi-meter.

Alternator died on the wifeys ///M3 with same symptoms last fall, the Alternator Light would only come on when the battery was extremely low and then with would flicker with the engine RMP and not stay on solid. Did exactly what MIKYZZ4 recommended and saw battery voltage dropping on multi-meter all the way down to -8.5 VDC. This is when I shut it off. Once new reman alternator was in place a snappy & constant -14.6 VDC was measured!

[squirrelhill]

Thanks for the input. I will measure the respective voltage outputs once the battery is fully charged and will report back. Before testing, I will also go through all the connections/grounds to ensure they are solid.

If the voltage tests reveal that the alternator is not charging the battery, should I start with pulling the alternator and having it tested or replaced (at least the VR), or should I first attack the battery bulb in the instrument cluster and/or the k61 unloader relay? I am dreading having to pull the alternator, but will if it is the logical next step.

What I can't discern from my research is whether a bad VR or alternator diodes will cause the battery light not to come on or whether the battery light must be working in order for the alternator to charge the battery.

[ZUUD BYE]

If you are not pumping more than -14 VDC to the battery running the alternator is bad, replacement is pretty easy, pull air box-maf-boot up to throttle body, move the power steering reservoir out of the way (leave hoses connected) pop the fan & shroud off, loosen Alternator pulley bolts, pop the serpentine belt off, unhook the electrical connections (I think 10mm and 8mm deep well will be handy) 2 13mm bolts and it's in your hands. Don't fret it.

RockAuto has reman Alternators for the 1993 M5 115 Amp $100 after core return and 140 Amp $120 after core return.
Captureq.JPG

[squirrelhill]

Closing the loop on this thread....

I tested my fully charged battery this weekend and it clearly was not getting any charge from the alternator. Also, I was not getting the red battery light with the key in position 2.

As a result, I swapped the alternator with a reman 140A Bosch compact unit from a reputable source. The battery now is getting 14.2 volts with the engine running and a couple of the accessories (radio, lights, etc.) turned on. The red battery light has also returned with the key in position 2 and quickly turns off when the car is started. The alternator that I pulled out was original to the car (28/94 build date) and certainly did its service as the car has almost 257k miles.

In addition to the alternator, I put in a new mechanical belt tensioner, new deflector/idle pulley and a new alternator pulley. After checking, I reused my serp belt as it has less than 2k miles on it and was in very good shape.

All in all, not a terrible DIY and the wagon is back in action... I am particularly pleased with the new tensioner and pulleys, as the bearing noise and belt chirp is pretty much gone. The car also feels a bit smoother accelerating from a stop.

[ZUUD BYE]

Closing the loop on this thread....

I tested my fully charged battery this weekend and it clearly was not getting any charge from the alternator. Also, I was not getting the red battery light with the key in position 2.

As a result, I swapped the alternator with a reman 140A Bosch compact unit from a reputable source. The battery now is getting 14.2 volts with the engine running and a couple of the accessories (radio, lights, etc.) turned on. The red battery light has also returned with the key in position 2 and quickly turns off when the car is started. The alternator that I pulled out was original to the car (28/94 build date) and certainly did its service as the car has almost 257k miles.

In addition to the alternator, I put in a new mechanical belt tensioner, new deflector/idle pulley and a new alternator pulley. After checking, I reused my serp belt as it has less than 2k miles on it and was in very good shape.

All in all, not a terrible DIY and the wagon is back in action... I am particularly pleased with the new tensioner and pulleys, as the bearing noise and belt chirp is pretty much gone. The car also feels a bit smoother accelerating from a stop.

+1
Excellent work!

[MIKYZZ4]

+2
Excellent work on the primary repair, and for thinking ahead,
and replacing the tensioner and pulleys as part of the operation!