Odd electrical issue on the E28

"HoustonRunner" (houstonrunner) 07/04/2019 at 15:14 • Filed to: None

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Interesting thing happened this week with the E28. After solving my idle issue last weekend I also took the time to do another minor task - cleaning the battery terminals.

They weren’t horrible, but these era BMW’s can be fickle to voltage, and numerous random issues can be attributed to a bad ground. I didn’t go through and clean each ground connection to the body, block, etc., just the terminal connections.

After that I took it on some “longer” trips around town, but even those were only 4 miles or so each way.

Yesterday I took it on two really short drives, basically a mile each way with multiple stop signs in between.

Backing into the garage after the second one I took it out of gear, set the parking brake, and with it still running tried to roll down the front windows a little since the car still smells a bit. (Haven’t had a chance to use the chemicals recommended earlier this week.).

Window didn’t move. Thought maybe I pushed the window lock button. Nope. No movement.

Ok, not cool, but not a big deal. Tried turning the car off and restarting it. When I turned the key back to on, only the battery light lit up, and I got no functional gauges when it started.

Definitely some electrical issue.

We were getting ready last night to go to a resort for the long weekend, so I didn’t have much time to troubleshoot the issue. I was able to use a multimeter and determine that with the car off it had about 12.4 volts, and with the car running and some throttle given to it I was getting 13.7 volts across the terminals. So I think the alternator is ok, but I’ll have to wait until I get back home on Sunday to get the battery tested.

But it does seem odd that this happened right after I cleaned the terminals at the battery really well.

Bonus Lake Michigan sunrise picture from my trip a few weeks ago.

Full of the sound of the Gran Fury, signifying nothing. > HoustonRunner 07/04/2019 at 15:42

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Look for a fusible link. If it’s anything like my E34 it will be in a little plastic housing inline with the battery cable, pretty close to the battery. I had done some detailing work under the hood and bumped this a little from its resting position of decades, and as a result all sorts of electrical things stopped working - windows, locks, seats, radio, climate control, etc., but the car still ran fine.

The holder for the fusible link isn’t sealed, so a little corrosion can build up. When you disturb it, the corrosion causes a separation of the metal mating surfaces and you get an intermittent connection. Take out the fusible link , polish it up with some emery cloth or something similar, and you should be fine.

HoustonRunner > Full of the sound of the Gran Fury, signifying nothing. 07/04/2019 at 15:52

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Wow, thanks.  I knew I should have brought my Bentley manual for pool side reading.  I actually would have trailered the car here if I had one, just so I could putter around and tinker with it.  

Full of the sound of the Gran Fury, signifying nothing. > HoustonRunner 07/04/2019 at 16:00

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It was the Bentley manual that helped me figure out this problem. I just traced the failed circuits back, looking for a common point of connection, and found them all in that one spot . Polish up the link, put a little dielectric grease on it (both sides) and the problem should be banished for decades.

HoustonRunner > Full of the sound of the Gran Fury, signifying nothing. 07/04/2019 at 16:07

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I can’t recall from your posts, do you still have the E34? As I was looking for the E28 there was an E34 540 in Tulsa that I considered looking at. Very happy with my E28 though. As soon as I get past a few other small issues I’m going to tackle the bumpers. I’m fortunate to have a brother in law who is good at metal work, so I think we can figure something out without dropping coin on euro ones.

Thanks again.

(Mye28.com is a great resource, but Oppo is a better community.)

Full of the sound of the Gran Fury, signifying nothing. > HoustonRunner 07/04/2019 at 16:14

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Nope - no longer have the E34. Sold it to a friend after a co-worker did a 5th to 1st downshift. I was quite poor at the time and really couldn’t afford maintaining an old German car, so I reluctantly let it go. I haven’t talked to him in years, but looking at Google street view it looks like he sold his E34 and kept mine, and possibly added an E39 M5 and a Vanagon, two of my favorite cars ever, to his fleet.

HoustonRunner > Full of the sound of the Gran Fury, signifying nothing. 07/04/2019 at 17:40

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E39 M5 is my "when the kids get out of college" car.

HoustonRunner > Full of the sound of the Gran Fury, signifying nothing. 07/09/2019 at 22:52

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So looking at the car and in the Bentley, no fusible link in the E28. I get a solid 13.8V at the terminals with the car running, but just 12.2V with the car off. I’m leaning towards bad cell in the battery.

Also left it hooked up for 4 days while out of town, and still had 12.2V when I got back, so I’m thinking no big parasitic draw.

Full of the sound of the Gran Fury, signifying nothing. > HoustonRunner 07/10/2019 at 00:51

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You might be on to something here. Take the battery to an auto parts store and see if they can do a free load test on it and see what that turns up.

If there are a number of items all failing at the same time, like on my E34, follow the wiring diagrams and see if there is a common item that could affect all of them. In the E34 it was the fusible link, but it could be a common ground that is corroded. But of course, get that battery checked out first.

HoustonRunner > Full of the sound of the Gran Fury, signifying nothing. 07/10/2019 at 09:06

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Borrowed a charger from my brother in law last night. When I hooked it up it showed low charge, but when I checked on it 10 minutes later the voltage needle was swinging between full and no charge, and the “Full Charge” light was blinking on and off in unison with the needle.

I don’t have the manual for the charger, but seems pretty likely that indicates a battery issue.

HoustonRunner > Full of the sound of the Gran Fury, signifying nothing. 07/13/2019 at 19:08

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I was just a fuse.  The one that controls the dash and windows.  It was pretty old looking, so I'm not too concerned about a lingering issue.

Full of the sound of the Gran Fury, signifying nothing. > HoustonRunner 07/13/2019 at 21:02

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I’m glad to hear that it was something simple. At this point I would suggest pulling the fuses one by one and giving them a little polishing with some emery cloth to get rid of any corrosion. This should make them last another 30 years.

BTW, did you order any of the Bosch books?

HoustonRunner > Full of the sound of the Gran Fury, signifying nothing. 07/13/2019 at 21:11

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Not yet, in my amazon queue.