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Thread: '85 K100RS Bad fuel pump or fuel pump relay?

  1. #1
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    '85 K100RS Bad fuel pump or fuel pump relay?

    Hi all,

    I have an 85 k100rs that has been ok till now. Riding along and felt something knock between my legs like a slight vibration. Bike coasted to the curb and would not start. Thought it was the loose plug on the COMPUTER ECU ECM CONTROL MODULE BRAIN BOX and unplugged and re plugged it in. Have had this happen in the past. Put a zip tie on it to hold in position. Tried again but no start. All seems fine, starter cranking, battery power ok, gas in tank. Could it be the fuel pump relay or the pump? And how do I figure out which one? http://www.bmwmoa.org/forum/images/smilies/dunno.gif

  2. #2
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    Open filler cap. Turn on key and kill switch. Tap starter button. You should hear the pump (in the tank) run for a couple of seconds.

    When you plug in the computer plug, you MUST remove BOTH battery covers and hold the rear of the computer with one hand as you are pushing the plug in the front with the other hand. You MUST hear a distinct CLICK when the plug locks into the computer.
    The computer is rubber mounted, so just pushing from one side without holding the back side allows too much flex to get the plug properly seated.

    IF you are sure the plug is properly seated, check your fuses especially #1 and #6. Check for voltage at #6 when the starter button is pushed. (only lasts a couple seconds, so have meter set up before pushing button. If you do have voltage, but pump doesn't run, you need to pull the pump and bench test it.



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    Lee Fulton Forum Moderator
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  3. #3
    Rally Rat
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    Does your bike still have the small battery negative cable (maybe 18 gauge)? If so, replace it with a later cable. The original, especially with some age, can give you fits.

  4. #4
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    Thanks 98lee. Did all of the above and have to pull the pump. How do you bench test it?

  5. #5
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    Put 12v directly to the terminals. No fuel connected, just see if it runs (probably won't). The small terminal is positive. If the pump does not rum, try reversing the polarity. It might unjam it. But it usually is fubared.

    A very cost effective replacement (I use these in all my bikes):

    http://www.euromotoelectrics.com/BMW.../fp-231kit.htm


    With the following adapter:

    http://www.euromotoelectrics.com/BMW.../> 576foam.htm


    If your vibration damper is going bad:

    http://www.euromotoelectrics.com/BMW...-576damper.htm




    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
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  6. #6
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    bench test

    Took out the pump and saw the err to my ways. I used a bead of gasket sealant (recommended by the garage I was in) that broke down in the tank and got into the pump. This raises several questions:
    1. What can I soak the pump in to try and loosen/dissolve and reverse pump out the bits?
    2. Did I even need the gasket sealant in the first place (to seal the gas cap gasket to the tank) and if so what is the correct one?
    Last edited by 117336; 08-29-2012 at 02:54 PM. Reason: needed more info

  7. #7
    3 Red Bricks
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    The screen cup on the bottom of the pump should not have allowed any solid bits into the pump.

    You might try spraying carburetor cleaner into the pump and then running it in reverse. Carb cleaner is flammable. Do outside. Solidly bolt wires to pump. Make/break connections with battery several feet away (sparks).

    No gasket sealer should be used, but a new gasket would be a good idea.

    16111453690 $8.37



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
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  8. #8
    BMW uber alles! Zagando's Avatar
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    Quote Originally Posted by 98lee View Post

    A very cost effective replacement (I use these in all my bikes):

    http://www.euromotoelectrics.com/BMW.../fp-231kit.htm


    With the following adapter:

    http://www.euromotoelectrics.com/BMW...> 576foam.htm


    If your vibration damper is going bad:

    http://www.euromotoelectrics.com/BMW...-576damper.htm





    Hey Lee; does your above statement mean that this fuel pump will fit/work in a K75S (with the foam adapter also mentioned)?

    Just gathering info in case I need to replace my screeching, chirping OEM 1994 fuel pump.

    Thanks!
    ---Jeff

    ex: K75S Berlina R100GS/PD , K100RS , R75/5 , R60/2

  9. #9
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    Quote Originally Posted by Zagando View Post
    Hey Lee; does your above statement mean that this fuel pump will fit/work in a K75S (with the foam adapter also mentioned)?

    Just gathering info in case I need to replace my screeching, chirping OEM 1994 fuel pump.

    Thanks!
    Not exactly. That info is for the 52mm pump replacement. You have the 43mm pump. You can get a better deal by going with:

    http://www.euromotoelectrics.com/BMW...231kitplus.htm

    It includes EVERYTHING except a new vibration damper.

    http://www.euromotoelectrics.com/BMW...kdamper694.htm




    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
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  10. #10
    BMW uber alles! Zagando's Avatar
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    OK, Lee; thanks for the clarification.

    That EuroMotoElectrics is a great source---I bought my new Westco battery from them Friday morning online and the battery was at my door Saturday morning---well packed and ready to go!

    Hope I don't have to replace the fuel pump but it (or it's pressure relief valve) is making such a racket I may have to do so soon.

    I'll try replacing the fuel filter once more and see if that makes any difference beforehand, though.

    Appreciate your help as always.
    ---Jeff

    ex: K75S Berlina R100GS/PD , K100RS , R75/5 , R60/2

  11. #11
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    Good news!

    Hey Lee,

    Thanks for your help and wisdom. Good news the pump works. How should I clean it and make sure there's nothing stuck? Also what is the best way to clean out the tank. Seems there's particles from the first time I did it so my way didn't do such a good job.

  12. #12
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    The BEST way to clean the tank is to drain it, remove it and wipe it out. Then let it dry out, invert it and blow it out with compressed air. Inspect and repeat.


    If the pump runs, there probably is nothing inside., but to be sure, you could fill a NON METAL pan (oil drain pan) with gas about 3" deep ( OUTSIDE!!!!!!). Connect LONG wires to pump and a LONG hose to the pump. Clamp end of hose so it will not whip around. Direct hose where flow will be contained (it will/should be at HIGH pressure). Run it, see what happens. Don't blow up the house. Keep fire extinguisher handy.


    What is the condition of the cup/filter on the bottom of the pump??? That really should have stopped anything solid from getting in the pump.



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
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  13. #13
    Themason 42906's Avatar
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    Quote Originally Posted by 98lee View Post
    The BEST way to clean the tank is to drain it, remove it and wipe it out. Then let it dry out, invert it and blow it out with compressed air. Inspect and repeat.


    If the pump runs, there probably is nothing inside., but to be sure, you could fill a NON METAL pan (oil drain pan) with gas about 3" deep ( OUTSIDE!!!!!!). Connect LONG wires to pump and a LONG hose to the pump. Clamp end of hose so it will not whip around. Direct hose where flow will be contained (it will/should be at HIGH pressure). Run it, see what happens. Don't blow up the house. Keep fire extinguisher handy.


    What is the condition of the cup/filter on the bottom of the pump??? That really should have stopped anything solid from getting in the pump.



    Take video for YouTube. We want to see the fireball !
    Experience is what you get when you don't get what you want.

  14. #14
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    done done and done

    Thanks Lee. Managed to not blow anything up and ran the pump in a plastic bucket of gas with a hose clamped to the output and rubber banded to the pump body. All working as it should with unmeasured pressure. Cleaned out the tank with gas and air dried it then compressed air and some shaking to get all the crumbs out. Ordered a new strainer as mine had a tiny slit in it and I mean tiny but I didn't want to take any chances. I saw there were 2 kinds of strainer available: one with a hose attachment and one without. Mine had none and is an 85? Where would the hose on the strainer connect to in the tank if it is supposed to have that? Thanks for your help and the links to parts. This place rocks and is cheaper and faster than anywhere else!
    Enjoy the long weekend!

  15. #15
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    On the later tanks there is an aluminum tube about 5/16 diameter hanging down about 2" from the roof of the tank just to the rear of the filler opening. I don't think yours will have it.

    Just buy the early filter cup (no longer available from BMW). http://www.beemerboneyard.com/16121455126e.html



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

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