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From digest.v6.n744 Sat Jun 7 17:45:32 1997
From: Nick Brearley <>
Date: Sat, 7 Jun 1997 16:49:04 +0100
Subject: E30 battery discharge solved

Some days ago I posted a question about the battery discharging while driving, even though the charging checked out OK. John Darwak, Mike Gordon and Bob Hazelwood were good enough to reply, their suggestions are attached.

Bob and Mike were right on the money with the voltage regulator - replaced on Monday - problem solved. Replacement is easy - two screws on the back left of the alternator. Removing the air box improves access, but is not essential.

For anybody else with ageing E30 electrics it might be worth noting the replacement Bosch part no. 1 197 311 090. This differs slightly in the last three digits from the original part but fit and function appear similar. It was probably the best 10 pound fix I've done on a car.

Nick Brearley
86 325i

>OK here's an easy one that I did once. You know that alternator idiot
>light in your dash? If that bulb is burned out your alternator won't
>charge the battery. Check the light and make sure it is working...
>John Darwak

>Sounds like the alternator or the voltage regulator is bad. But
>first, don't overlook items like bad connections at
>battery/regulator/starter and bad grounds.
>Alternators can operate intermittently also--I had an alternator for
>my Mazda RX7 Turbo that I was sure was bad. Took it to PepBoys to
>have them test it and it checked out ok. The alternator was cold.
> When operating in the high underhood temps, it would fail. So I
>replaced the alternator and life is good again.
>Hope this helps,
>'87 L6

>I had the exact same symptoms in my '87 at 240,000 Miles. My alternator
>also checked OK, but the problem indeed was the alternator. More
>specifically, the voltage regulator; which is a small black plastic
>assembly held into the rear of the alternator, was bad. This assembly
>contains the commutatator brushes, which wear out. In my case, the
>brushes were worn such that they didn't make good contact when they were
>vibrating on the road, but when the car was in the garage the alternator
>checked fine with the traditional tests.
>Replacing this part is an easy DIY project, and it's relatively
>inexpensive. The regulator was $34.95 for the OEM part at Bavarian
>Autosport. (A local auto parts store tried to charge me $212 for some
>aftermarket part, so be careful!)
>Hope this helps.
>Bob Hazelwood

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