frank horton
V twins are great but 4"s rule.........
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- 3,816
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- Crete, Greece
oh, the wonders of modern vehicles..........
Had a e61 last year in with similar issues as yours, after fixing starter motor at another garage, new battery programmed in and we changed the alternator. These bmw use 150A and higher diodes which aftermarket cannot source reliable units and most outfits fit lesser Amps diodes in the rectifier pack and hence the issues. Coupled with the computer needs to know what battery capacity it has so the alternator CAN charge it reliably ! On the positive power lead there is also a power interrupt pirotehnic fuse which can also blow off at light impacts- check if it hasn’t been tampered with- scan for codes and look for heat discoloration on power wire either side of the fuse. It’s not available separately and bmw charge a bit for a new lead. I would make sure that alternator doesn’t charge more than 14.4 volts, there are many electronic boxes of trickery inside the car that doesn’t like fluctuating voltage !15.1v sounds high.
We had an V8 X5 that would randomly go into transmission failsafe mode and then the car would cut out.
Turned out to be the alternator.
I have a 328i F31, I could measure the charging voltage as a double check but I’d of thought 14.4v would be the max.
Can you replace the regulator without swapping the entire alternator.
As to trying to bridge the solenoid..almost impossible as it's mounted on the starter motor and completely hidden in the depths and under all the engine covers