BMW K bikes (Bricks)

You are not connected. Please login or register

View previous topic View next topic Go down  Message [Page 1 of 1]

1Back to top Go down   Motronic or fuel pressure defect? Empty Motronic or fuel pressure defect? Wed Jun 10, 2020 7:20 am

geoff barnett

geoff barnett
active member
active member
Can members please advise. 

After some years on non use I am recommissioning my 1985 K100RS.

She has a good spark, has new fuel in the tank, new spark plugs, new air filter, new battery, new fuel pump, new fuel filter, s/h Motorworks fuel pressure regulator, all injectors professionally serviced.

Action. Engage "choke" (fast idle), turn key, ignition lights are good, press starter button, fuel pump whirrs away, starter motor turns, the engine starts - and then just as quickly she stops. Repeat as before. Same.

As per above, I've checked the fuel delivery side. All seems fine.

Last night I was watching an old car show on TV. In the program a technician had a similar problem with a fuel injected V8. He concluded that the fault was an airbox flow sensor failing to operate. The computer detected this non return, and because there appeared to be no airflow, shut down the ignition.

In like manner on my K100RS, could the Motronic fuel injection control unit and the ignition control unit be conspiring to produce the symptoms that I above describe?

How do I test the ignition control unit and the fuel injection control unit?

Or am I here barking up the wrong tree?


Rick G

Rick G
The only way to test them is to swap them for known good units. Both units rarely give any trouble and an 85 will have a L-Jetronic as opposed to a later 16 valve which has the motronic system.
The injectors are controlled by the ECU but the ICU supplies an earth to the so the pump will run before the engine turns over. I would suspect that this is where the problem is in that when the start button is released the earth is removed and the ICU thinks the engine is not running and stops the injectors firing by stopping the pump.
Keep the start button depressed that way you will isolate where the problem is. Don't be concerned about the starter spinning as if the engine is over 711rpm the starter will not work.

"Man sacrifices his health in order to make money.
Then he sacrifices money to recuperate his health.
And then he is so anxious about the future that he does not enjoy the present; the result being that he does not live in the present or the future; he lives as if he is never going to die, and then dies having never really lived."   Dalai Lama

Bikes 1999 K1100 LT with a Big Block 1200

92KK 84WW Olaf

Life time member
Life time member
Disconnect the unit under the seat and clean the pins on it too. Electrical/connection issues as opposed to component issues are very high on the list. If you have any K lovers near you [there are number of them on here] a quick swap over of the unit under the seat is a good move for beer money, only takes a couple of minutes and either fixes it or tells you its a good unit by working ok in the other K. All K100 2v ones are the same for that unit under the seat.

1992 K100LT 0193214 Bertha Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red 578 bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 689 58,645 now 106,950 miles Deceased.
1983 K100RS 0011157 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 58,200 miles. 
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles currently 48,061 miles.
1983 K100RS 0004449 Odette R100 colours 58,000 miles. Sprint fairing now 61,190 miles

1968 Yamaha 80 YG1
1971 Yamaha 125 YAS-1
1968 Honda 125 SS
1970 Honda CD 175
1973 Honda CB500-4
Honda CX 500

Sponsored content


View previous topic View next topic Back to top  Message [Page 1 of 1]

Permissions in this forum:
You cannot reply to topics in this forum