BMW K100 RS 8v 1985 fuel/ECU breakdown - Crinkly Dave
Just partially rebuilt the bike, unused for a year, but prior to that used to tour the continent. Started up OK and today used to go to the MOT station where it failed for loose handgrip only. On way back after ~10 miles, with water temp at 80C and no problems it suddenly died.

Fault traced to fuel pump relay not functioning. It works if we earth the yellow & brown cable which goes from connection 85 of the relay to connection 7 of the ignition control unit.

Manual suggests "fuel supply will be shut off" if there is a high water temp, or other fault which turns off ignition, but I assumed this would mean isolation of the injectors usually. Certainly the injectors will be turned off on overrun until the revs drop to 2000, but not the fuel pump?

Ideas before we try bypassing the ignition unit?

Pig to work on, as access to the relays means tank removal etc

Crinkly Dave (new and improved with Italian aortic valve!)
BMW K100 RS 8v 1985 fuel/ECU breakdown - Crinkly Dave
Ah, may have solved it myself. Manual says pump is only energised with engine running OR starter pressed, so what we now see may be correct. However, ignition unit also turns it off if it senses the ignition has failed.

Must look later. Then to find the original fault.
BMW K100 RS 8v 1985 fuel/ECU breakdown - Crinkly Dave
All sort of sorted. Tried power to pump with starter pressed, and all ok. Put power supply to pump and it run. Built it all up, and all seemed to work OK for 20 mile test.

Suspect poor connection at one of the joints, but all require tank off to check.

Must now get cheque book out to pay for the thing. Too wet to even walk out to garage!
BMW K100 RS 8v 1985 fuel/ECU breakdown - SteVee
Glad to see a K100 still on the road - I did like the design, but like the Porshe 911 series, the boxer twin just had to come back - just too much of a classic I suppose.

Finding a poor connection can be very difficult - I hope you resolve it.

This has to be the quietest bike caff I've ever been in ! Especially if the weather's wet.