BMW K bikes (Bricks)

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1Back to top Go down   Problem with FI relay Empty Problem with FI relay Sat Oct 26, 2013 2:58 pm


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Problems getting bike up and running. Narrowed it down to ground from ecu to pin 85 on fi relay. Have continuity on the wire from pin 7 of ecu to pin 85 of the relay, but when I try to start it, it is getting voltage from somewhere. I can run a wire from ground to back of relay and it will start. Does anyone know where i might be losing this ground from the ecu or will i just have to replace the ecu? sorry did not mention what bike. It is  1985 K100rt.


2Back to top Go down   Problem with FI relay Empty Re: Problem with FI relay Sat Oct 26, 2013 3:49 pm


if the pin going to the ecu is lossy or the cable has some resistance
you will see voltage on the negative side of the relay after the start process has been initiated ...other wise with power on there should be positive on the earth side as well ...its when the ecu switches on ( to ground ) that the voltage drops

might be worthwhile doing 2 things

take the connector off ...and clean up both contacts ...(ie  the connector strip to the ecu pins ....and the socket side as well )

 make sure that there is a good earth to the ecu from the frame ground  by the mounting bolts
....near the ecu itself there is a bolt through  the frame ....with several lugs under that bolt ...clean it all up

some folks have done this but missed at least one lug under the bolt

btw make sure that the ground cable from the battery to the gearbox mount is clean and good contact ....highly recommended to upgrade this cable as well to at least 8mm

cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%O

'86 k100 rs.. #######..  "Fred " (f(rame) red ) ( Fredrick leichtundschnell ) - -
bits and pieces from many kind friends across the k100 world ...with many thanks ..

1987 k100rs ########   "Red"  - (red sports rs TWB style )

3Back to top Go down   Problem with FI relay Empty Re: Problem with FI relay Sat Oct 26, 2013 4:14 pm


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Life time member
Since Hall Effect sensors usually go out gradually, my guess is that it's either the ICU (called that on a K because it only controls the ignition while the L-Jetronic controls other engine management functions) or the yellow/brown wire from the ICU to the relay is faulty.

First check that you have good continuity from Pin 7 on the ICU connector to the yellow/brown wire to the FI relay to see if the wire's good.

If it's not that then I'd guess that the ICU has gone bad.

Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
98 Taxi Cab K1200RS
14 K1600GT

4Back to top Go down   Problem with FI relay Empty will do Sat Oct 26, 2013 6:58 pm


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New member
Thanks, will pull grounds and clean them all good and retighten. have tested the wire from the pin of ecu to the relay and show good continuity there.


5Back to top Go down   Problem with FI relay Empty Re: Problem with FI relay Sat Oct 26, 2013 7:07 pm

92KK 84WW Olaf

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Life time member
Used ICU units are readily available too.

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 54,800 miles. 
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles currently 42,640 miles.
1983 K100RS 0004449 Odette 55,000 miles. Sprint fairing

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

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