1991 E34 Electrical Problem? - BMW Forum

MikeGE · 04-25-2009, 10:56 AM

Hello all,

I am new to this forum (joined today) and have a problem with my 1991 525i E34 M50 that is puzzling, at least to me. I have searched the Internet and this forum for a similar situation, but could not find one.

Last night as I was driving home from work, the SRS light on the dash came on. About a kilometer later, one of the other dash warning lights came on and then then I noticed that the headlights were getting dim.

As I braked for a traffic light, the engine started running very rough and the whole car started shaking as the engine surged. When I turned off the lights and heater, the surging stopped, but started again when I turned the lights back on.

When the traffic light turned green, it took me about 20 seconds to crawl through the intersection. Fortunately, there was no traffic and I limped to a place to stop. By the time I coasted to a spot, the engine had died and there was very little electrical power left to illuminate the interior lights.

My first thought was the serpentine belt had broken and I had been running on battery power alone. When I opened the hood, everything appeared as it should. The belt was intact, there were no signs of any fluids leaking, and the alternator was cold to the touch.

After about five minutes of scratching my head, prodding relays, and tugging on cables, I noticed that the interior lights were now bright. I turned the ignition key and the car started fine and ran as if nothing were wrong. Even turning on the headlights and heater did not cause any changes in RPM or cause any warning lamps to illuminate. Since I lived about one kilometer away, I drove home without a problem.

Today, I decided to drive to the next town, which is about 15 kilometers away. As I neared an intersection, the SRS light came on and about 30 seconds later, all of the dash instruments died, followed quickly by the engine.

When I tried to start the engine, there was nothing. After about five minutes, it appeared as if all power was restored, except the car still would not start. The starter motor would engage, but after one attempt to turn, it would stop. It had the appearance of a dead battery.

I called ADAC and waited for about 15 minutes, all the while making new friends at the busy intersection. On a whim, I tried to start the car and as it did last night, it started without a problem.

Five minutes later, when I was almost at my destination, the SRS light came on, but I had parked before the total power loss occurred. The car remains where I parked it and my wife picked me up.

If I can rule out demonic possession, what could be causing this problem?

If it helps, here are more particulars about the car.

It has about 295,000 kilometers on the original engine
Automatic transmission (replaced ten years ago)
New thermostat (previous thermostat failed open)
I keep getting the coolant level warning, even though the level is fine.

I appreciate any help!
Mike

marti5 · 04-25-2009, 01:16 PM

It definitely sounds like a low voltage problem to me, check the batt connections , then get the batt checked, also check all your fuses are nice and tight in their holders.

MikeGE · 04-25-2009, 01:51 PM

Thanks, I will check everything tomorrow. I do not understand why sitting for fifteen minutes restores the electrical system to normal.

MikeGE · 04-25-2009, 03:39 PM

I was wrong about the light...it is the ABS light that comes on, not the SRS light.

CosmosBlack · 04-25-2009, 08:18 PM

Mike, sounds like a similar problem posted by another member recently.
Take a look at the fusible link, it's a piece of metal/fuse, usually in a small black plastic box that clips open/close, cose to the battery. It's attached on a power cord that leads to the battery. Open that box, there are 2 bolts holding the fusible link on both ends. You have to loosen the bolts to be able to determine if the fusible link is broken. Just looking at it can be misleading. IF it is broken, you found the problem, very cheap fix. And a very common problem in older Bimmers.

If it's not the fusible link, the other thing that I can think of is the ignition switch.

Good Luck!

CosmosBlack · 04-25-2009, 08:27 PM

Found some pics of a E34 525i showing the fusible link:

MikeGE · 04-26-2009, 10:07 AM

Thanks CosmosBlack,

I checked the link and it was fine. Marti, the negative lead of the battery was corroded, but I think I found the problem. It does not show up very good in this picture, but the brush closest to the transistor does not show any signs of wear, nor does the mating ring in the alternator. Off to the dealer tomorrow. Thanks to everyone!

Contrary to what I read, this was NOT an easy task. It might be easier to access some of the hardware from below the car, but I was working on the street and did not have access to a lift.

After fumbling around for an hour trying to take the wiring harness off the alternator, I decided to remove the two mounting bolts and maneuver the alternator around to remove the harness nuts.

H2SNOW · 06-11-2009, 02:49 PM

wow man ...like deja vu same thing happened to me ..and mine was the srs light that came on then other warnings ..dead coasted to the shoulder ...same thing ..couple minutes later all the lights were on no big deal ..barely started then did it again fro where I was on the shoulder to about 200 feet away off the road..

put on battery pack started up and ran to my mothers house no biggy ...thought the battery was done ..went and bought a new battery zoomed home ..worked fine

then got up in the AM ..car was dead ..no lights no nothing and the brand new battery was dead ..

now what ...alternator ???

mine is a 94 540

MikeGE · 06-11-2009, 04:55 PM

My problem was fixed by replacing the voltage regulator. I had to jump start the car as well since everything was running off of the battery until it died.

Installing the regulator and putting everything back took about 45 minutes and it runs fine now.

H2SNOW · 06-12-2009, 12:35 PM

did you have to pull the rad to get the alternator out ???

is there a test to determine the voltage regulator ??

and I assume the regualtor is part of the alternator ...

MikeGE · 06-12-2009, 01:58 PM

I did not have to remove the radiator, but I did have to remove the shroud and the air duct that connects to the alternator. I tried for over an hour to remove the rear housing on the alternator, but since I was working on the side of the road, and not on a lift, I could not access one of the nuts and a screw.

Removing the alternator mounting bolts allowed me to maneuver the alternator around to remove the two nuts on the wiring connections and then remove the alternator from the engine bay. Once out, removing the rear housing, and then the regulator was a breeze.

The most difficult part, once I resolved to remove the alternator, was removing the bottom mounting bolt. The nut on the bolt is accessible only after removing the top bolt and moving the alternator out. then the process is slow because of the close confines.

The regulator is the item that is in the picture in my post and is inside the alternator, but accessible from the end. If the dealer had the brushes in stock, I would have replaced them, but I called six dealers and none had them. Therefore, I had to buy a new regulator at EUR 77.10 (about $110) instead of the relatively inexpensive brushes.

I am sure there is a test for the alternator, but not in the residential area where I stopped. I could have called ADAC to have it towed, but where is the fun in that

H2SNOW · 06-12-2009, 03:07 PM

I guess your engine bay isn't quite as cramped as mine ..the ole V8 doesn't leave alot of room ..

thanks for the input

H2

jbrizzuto · 09-10-2009, 02:03 AM

"prodding relays, and tugging on cables, I noticed that the interior lights were now bright"

I have a'94 525i and a few yrs ago and my wife backed into a stone wall resulting in the rear bumper hanging off. Took the car to a body shop and they kept the car for months waiting for new parts to come in. When I got the car back I had all kinds of electrical problems from mice eating the wires. Dealer wanted something like $4000 to replace wire harness. I had the mechanic try to repair the wires as much as possible but always had intermittent electrical problems. I finally located a shop that specialized in BMWs and they were able to repair all the electrical problems.

So maybe you have some wire problems. Inspect the wires under the hood looking for insulation that may have been nibbled off by mice. Good Luck!

MikeGE · 09-10-2009, 02:24 AM

The prodding and pulling on wires was a red herring. During the time that I was trying to troubleshoot the problem, the voltage regulator cooled down enough that it worked...for a while. Had I sat on the side of the road and read a book for the same amount of time, the results would have been the same, as I found out while waiting for the ADAC to arrive the last time. As soon as I removed the regulator, the problem was obvious and the new regulator has been working perfectly.

However, I had a problem with my Jeep Cherokee that was similar to your experience. The local shop replaced the radiator and somehow managed to position the wiring harness under the mounting boss of the radiator. Over time, the wires were cut and the instrumentation in the Jeep stopped working, but in phases. Eventually, smoke billowed from the hood when one of the battery wires was shorted. In the mean time, the shop spent about 20 hours total trying to isolate the problem..the fire helped.

jbrizzuto · 09-10-2009, 09:15 AM

Just goes to prove that there can be many different causes resulting in the same problems.