Well folks, I think the mystery has been solved. After replacing several parts and checking components, I was able to get three 30 minute test drives yesterday without incident. I'll feel more comfortable (after some out of town company is with us this weekend) taking a few longer drives early next week to better ensure I can make the 500+ mile (each way) drive to Hilton Head the week after next. To recap, I've had the crankshaft position sensor replaced, rebuilt the ignition switch and replaced the coil. After all of that, the car was still shutting off and sometimes switching back on but more often needing a restart or two to get running.
Don Lawrence and Chris Pederson suggested looking at a few more things including my starter wiring, battery and, finally, the ECU and fuel pump relays. So I removed my ECU from its bracket above the glove box to expose the two relays and first replaced the ECU with a good spare I had. Two test drives later, the shutoff only occured once or twice and so I replaced the fuel pump relay after that. Same results - fewer shutoffs but not eliminated. Chris P then noticed from one of my photos I had sent him that the relays were not securely anchored in their plastic receiver and I tried tightening them both but a secure attachment didn't seem possible. He suggested some zip ties next around the whole unit and I did that, two per relay. After trying to restart in my garage, the car would turn over but not start and she exhibited some strange mechanical noises like a starter struggling..she did fire up eventually but then quickly died out. This was a new problem. So I went back to the ECU relay, thinking the zip ties were on too tight and they were. Removing one of them on the ECU relay seemed to return the relay to its proper orientation and she started up and ran well for the three drives mentioned above.
For now I've returned the relays to their position above the ECU and anchored the whole assembly like before and I won't touch anything until after Legends of the East!
Wish me luck next week that the test drives continue to be uneventful so I can take my girl down south with Andrew and Doug on November 3.
It's really amazing living with these cars after so many years and experiencing the weird mechanical issues you encounter along the way, many of which seem to have no precedent on this board. You learn a lot about how older BMWs work, and cars in general, of course, thanks to the folks on this board and my trusty mechanic/technicians in Alameda. But it also deepens the bond with our cars and our E9 community when perserverance and some sweat and tears gets you to a solution and a better way of keeping our cars running well. (My solution is temporary for now and will need attending to after Hilton Head for a more secure and lasting fix).
At least I shouldn't have to worry about the crankshaft position sensor (which showed some cracks in the wiring near the sensor) or my coil (which also had significant cracks in the plastic casing around it) in future trips.
Thanks all, and especially to Don and Chris P! (I hope this is my last post in this thread.)
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Wayne - Let's return, shall we, to the 2017 Vintage. I recall driving in the pouring rain when Tom signaled me that he needed to pull over. His drivers' side wiper blade had departed his vehicle at speed and he was left without a wiper in the pouring rain. We pulled over, switched the passenger side wiper to the drivers' side, and safety wired it on so he could make it home.
Now, if I remember the sequence correctly, during the stop to repair Tom's car, you had a hard time restarting your car. I remember giving you a jump, which for some reason got you going again.
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You then had trouble restarting later at the pump when we stopped for gas.
After we got home, Tom determined the problem was electrical, and, I think he did a wiring repair in your trunk. Not sure if this was fuel pump related; memory is a little hazy here. Anyway, I toss this out there following up on Arde's comment.
and to Chris Ohmes, I thought I replied to your post but I gess not - that problem then was caused by a wire to the fuel pump shorting out against a seat rail. Once Tom Baruch found that out and reinsulated the wire my problem went away.
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Glad it's fixed, at least now if you have troubles on the way you know where to fiddle.
