Electrical shut-down

[travelinbamaman]

hey guys-have a 98' 528 that is losing electrical power when the temperature gets hot and/or the car has been running for a while. First the CD player/radio goes out, then blinkers, then the AC fan blower, open door warning lights come on, etc... Engine continues to run fine. Everything returns to normal after the car has sat overnight then the repeats the same scenario in the same sequence. Had the car in the shop and they replaced the ignition switch and said it was fixed..went later to pick up the car which had been sitting outside in 90+ temp and went to start the car and the problem was still there. My mechanic is stumped and so am I. Any ideas?

[jeffreyb4me]

The ignition switch is the most "common" failure but obviously wasn't your problem. Your mech. will have to do some actual circuit diagnosis and with a schematic and an existing condition it shouldn't be 'too' difficult to isolate.

[travelinbamaman]

finally found out that although the alternator was charging it was also intermittedly spiking and freaking everything in the electrical system out. Replaced it and so far so good.

[KC Ron Carter]

But for the lurkers there is a cheaper way to fix a charging system.

Here is a picture of new and old.



Alternator Regulator

They can wear into a grooved pattern and the impact of driving can make them vibrate out of the normal groove.

Since the regulator has to increase output to jump the gap it does.

You can clean up the slider rings with abrasive paper.

You can get the brushes as a separate part requiring soldering skills or you can get a Regulator brush assembly for $20.

Some instruction for changing:

It is a very touchy installation and about 5% of the installation end in the ground link bent and the alternator not functional.

You can remove correct and reinstall the regulator.

The output must be 14.25 or higher on a Volt Ohm Meter not the dash gauge.

Some hints on the regulator change.

Replacing Alternator Regulator

For those who work on their cars and have not had alternator problems, here is a simple action that should save you down-time and significant costs.

Most alternators on German cars fail due to brushes wearing down (as they are supposed to) between 150k and 200K miles. Brush replacement is very easy -- it should not take over 20 min. and the brushes are attached to a new regulator.

To replace regulator assembly -- back of alternator held in place with two straight slot headed screws. This has a round transistor mounted on the outside on Bosch alternators -- the other type is similar but uses different brushes. Pop the regulator out, after removing the screws.

Fitting the regulator back is simple, but you must install it starting at an angle, to assure that the brushes compress when the regulator is flush with the alternator and the screws are tightened.
You are now ready for 200K miles of alternator life.

[kellymdenver]

Hey all...I replaced the alternator in my 1991 525i about a year and 10k miles ago...doing the same thing as last year...I am going to install this one myself but there are three alternators listed...80 amp, 105 amp and 140 amp...which one should I buy?

Thanks!

[jeffreyb4me]

Despite the 'options', You need the same Brand [Valeo or Bosch] for replacement, there were only a couple of choices the factory used anyway, and only what came on your car will actually fit the brackets and harness.

[kellymdenver]

Originally Posted by jeffreyb4me

Despite the 'options', You need the same Brand [Valeo or Bosch] for replacement, there were only a couple of choices the factory used anyway, and only what came on your car will actually fit the brackets and harness.

Thanks Jeff!