BMW K bikes (Bricks)

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active member
active member
Hello to every one,
May be with your help I can solve a mistery of fuel pump....and injecton....

I have a problem that I can't solve by my self, I'll try to explain:
For a while the bike, a K1100LT 93 ABSI, had ignition problems due to the fuel pump sometimes not starting.
Waiting a minute and turning off the ignition the pump was back to normal.

A few days ago, after a little trip, I turned off the bike and after half an hour, to go home, I tried to turn it on again but the bike didn't start anymore and still not working on.

When switched on, the whole panel lights up normally but the petrol pump does not start.

I thought it was burnt, so after disassembling it I tested it by feeding it with a battery and it works perfectly, by the way the pump is original from 1993. (65000km)

I then continued searching the fault, I disassembled the float and replaced it with a spare one I had, I checked and it worked perfectly and everything was fine at least by connecting the float directly to the battery it jumping the 4pin connector.

I reconnected the 4-pin connector and tried to restart again.. the pump remains silent, the float works and the reserve light also works well.

I started checking the electrical circuit and verified that:
1) the relay it works and closes the contact regularly.
2) fuse n°6 is fine
3) fuse n°1 is OK
4) voltage at the relay connectors is correct
5) kickstand switch it works.
6) Four-contact female connector (the one to be attached to the tank connector) has these values with the key inserted:
6.a) pin green-brown cable 11.8V
6.b) 12V white wire pin
6.c) the two remaining voltage 0 pins

Then I tried to unplugg the tank connector and making a bridge between the female and male pin of the green-brown cable and grounding the tank, and turning on the Killer switch, the pump turns on and runs for a few seconds then it stops as per normal operation.
Reconnecting the 4-pin connector pumps shows no signs of life.

I have read here and there on various forums that there could be interference from the various injection organs which would justify this failure due to blocked injectors or in any case lack of pressure in the injection circuit.....but all message was not complete about the end of histories.

I've come this far but now I don't know what to do.
Any suggestions??
Every comments are welcome!!



Life time member
Life time member
The four pin "tank" connector is the source of much anguish to the owners of classic K bikes.  It is arguably the most unreliable part of the whole bike.

Many have replaced it with other types of connectors.  If you search here and other forums for K bikes you will find many references to repairing this problem.

1994 K75RT
1991 K100RS

1988 K100RS SE
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175


Life time member
Life time member
As Point-Seven-Five says, you have eliminated everything else except the tank connector. When I restored my LT I found that the white wire in the tank connector was broken, so I cut the connector off and replaced it with an aftermarket one. When the tank is replaced it is very easy to trap the tank connector against the frame and break the wires.

1983 K100 upgraded to K100RS spec, 1987 K100RT
1978 Moto Guzzi 850-T3, 1979 Moto Guzzi 850-T3 California,1993 Moto Guzzi 1100ie California
2020 Royal Enfield Bullet 500


Indeed, the connector is toast.

Before I would recomend the Superseal replacement, but as it is a flat inline connector, now I recomend the Deutsch connector.

Take the 4-pin black with stamped terminals.

K1100 LT ABSI 1993 - Trouble with Fuel pump DT4-N-SF-BK

Simply crimp them whith cheap AMP pliers;

K1100 LT ABSI 1993 - Trouble with Fuel pump Unior-amp-tang-3838909058061-0-l

K1100 LT ABSI 1993 - Trouble with Fuel pump Eu-log10  K1100RS/LT - R1200RT - R1100RS (RIP) - Cagiva SST 350 Ala Verde - K75LT project - K75 Schurgers - K75S


active member
active member
Thank you for suggestion.
I hope have manner to spend some hours tomorrow I'll let you know....
K1100 LT ABSI 1993 - Trouble with Fuel pump 112350


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