electrical issue - could my fusebox be toast?

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shadofax
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Location: Seattle WA

electrical issue - could my fusebox be toast?

Post by shadofax »

He everyone. I'm not a happy camper right now but she is 32 years old...

I have 1987 635 L that I've had for a year with no issues until a few weeks ago. She is my daily driver as well.

A month ago I was driving and she just cut off. I pulled over and she restarted right back up. I looked at it as a warning, as at the time I had no idea what caused it. A week later, I was driving to the store and to get gas and she did the same thing. Now, the second time was a lot more than a warning! I got her started again and, skipping the store, I stopped for gas (I didn't have a choice I was getting close to empty!). This time, she wouldn't start. She turned over fine but sometimes when I turned the key off the starter would keep going... After about 20 minutes she started and I got her home.

I was thinking it was the ignition switch and when I researched the forums, it sounded for sure I was right and so I ordered a new ignition switch.

The day before yesterday, I tore the steering column and installed the new switch. Before putting everything back together I tried to start her and she started right up twice - I was happy! But when I put everything back together she once again would not start! So I tore it back down and checked everything. Nothing wrong...

I checked all the fuses and they looked good. I had a friend have me try to start her up and he began by tapping on a relay. She started. I checked the relay (K5 - fast relay) but it seemed to have to do with the A/C. So, running, we pulled the relay and she kept running. We swapped relays and she still ran.

We tested all the relays with a tester and only one was questionable but she ran fine without it. I was left scratching my head and not feeling so good so I headed out once again to the store and from there I was going to pick up a few relays. -one to replace the questionable one and one as a spare. Well, she died on the road again! This time I got out, tapped a few relays and she started for a few seconds and died. I did it again and she started and I headed home again.

So I'm left thinking it has to do with the actual fuse box. I haven't looked but I'm guessing that this isn't something I can do myself and isn't going to be cheap. I'd like to know for sure if the actual fuse box is the issue, or am I missing something?
All the wiring that I can see looks good but to be safe I was going to replace/add some grounds (she is old and I've found that replacing grounds on old cars can elleviate a lot of electrical issues!) but that isn't going to solve this issue...

Any ideas would be GREATLY appreciated! I plan to drive her across the country starting in the second week in December - she has been so solid I had no concerns, but now....
1987 635 L
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86_6series
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Re: electrical issue - could my fusebox be toast?

Post by 86_6series »

I doubt it will be anything you find in the fuse box.

It could be any number of issues. You have to methodically go thru each system

to see which one is giving you the problem.

I would start with a vacuum smoke test first to see if you have any leaks.

You can use one of these with smoking chips, a hose from the spout into the tip of a plastic soda bottle

with the bottom cut out and attach to TB and puff away.

https://www.walmart.com/ip/Ktaxon-Bee-H ... b547a406a9

Then after your sure of no leaks use this to guide to test for other possible problems.

http://www.hiperformancestore.com/motronic.htm

You must find out what the issue is before guessing and installing parts you may not need. Good luck.
86-635CSi
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98-740i
71-Continental MK3
shadofax
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Re: electrical issue - could my fusebox be toast?

Post by shadofax »

Thank!

My only reason for looking at the fusebox is that every time it has died, I've been able to tap (lightly) on any of the relays in the fusebox and she will start right up again...
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whiskeydry
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Re: electrical issue - could my fusebox be toast?

Post by whiskeydry »

As a start, I would pull the main plug from the fuse box and check the connections are good. I had a loose 12v pin to the coil here which gave the same symptoms as you describe (thick green wire). I would also spray as many contacts as you can with contact cleaner and clean all spade connectors and fuses with fine wet and dry paper. Good luck.
Phil
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bakemono
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Re: electrical issue - could my fusebox be toast?

Post by bakemono »

Need to find some way of narrowing down the problem, since there are a number of things that could cause the engine to stall out while driving. When it happened, did the tach drop to zero instantly? Or did it come down gradually as the car slowed? If it was the former, that suggests that the ECU cut out for some reason. Could be an issue with the ECU electrical supply, speed/reference sensors, or the ECU itself.

Otherwise, if the engine lost power but the tach still showed a reading, it could be a fuel/ignition problem.
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Re: electrical issue - could my fusebox be toast?

Post by Pod »

Having read this thread a couple of times, it appears to me that you may have some wires which have overheated and melted together.
shadofax
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Re: electrical issue - could my fusebox be toast?

Post by shadofax »

I'm systematically going through the fusebox/fuses/relays... Cleaned all connectors, applied dielectric grease. checked all fuses and checked relays. found 2 relays outside the fusebox to the left, that should be the fuel pump relay (probably why she won't start) and the oxygen sensor/heater relay accounting the the BMW wiring diagrams I have.

The BMW shop didn't sound 100% sure on the relays and the one (fuel pump) cost $86.00 and has to come from Germany so I'll see when it comes in...

Does anyone know of anyplace else that might carry these?

My one fear is they said the fuel pump relay (4 prong) is the same as the "K" relays inside the fusebox. I was surprised, thinking these would be more common and cheaper...

Any thoughts?
1987 635 L
shadofax
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Re: electrical issue - could my fusebox be toast?

Post by shadofax »

oh, and when she stalled the gages slowly came down. -they did not cut out :-)
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Re: electrical issue - could my fusebox be toast?

Post by bakemono »

shadofax wrote: Wed Nov 06, 2019 12:08 am oh, and when she stalled the gages slowly came down. -they did not cut out :-)
Fuel pump circuit seems plausible then...

On my 633 the FP relay is a BMW part and it's rated for 30A. But there doesn't appear to be anything special about it. I can swap one of the Hella relays (for head lights, etc.) into that spot and my fuel pump still works fine. I don't know what the current rating of the Hella ones is, but a generic 30A replacement should be easy to get. I just did a search for 12V 30A relay and the first result was a Dorman for $4
'82 528e - M50B25 + GS6-37BZ
'83 633CSi - Megasquirt and a 3.46LSD
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