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Thread: '87 K100RS no start, spraying fuel!

  1. #1
    Registered User Sailingfool's Avatar
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    '87 K100RS no start, spraying fuel!

    First let me say I have researched the excellent trouble shooting guide for this, but I my issue isn't addressed. Let me give the scenario. The bike has 155kmi and has otherwise been running strong. One day I'm running errands around town. After parking and a quick stop, I mount up and attempt to start it. For the first time ever, it's reluctant to start. I smell gas. A visual inspection reveals nothing. Trying again, it fires up, and seems to run fine. My next stop is long enough to cool the bike down. When I attempt to re-fire it a couple hours later, it doesn't start and again the fuel smell. This time, I find fuel dripping, which I trace to the collector for the exhaust system, which it the lowest point!

    After trailering the bike home, I pull the plugs, and raw fuel pours out of all of the cylinders! What now? Fuel pressure regulator? Fuel pump? Fuel injection wiring?

    Any ideas are appreciated. The nearest dealer is a 250 mile round trip, and has the rep for replacing expensive parts until it runs (@$90/hr) but I'm not too willing to do that on a bike this old!

    Thanks in advance.

    JC

  2. #2
    3 Red Bricks
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    If you suspect that the problem is too much fuel rather than no spark causeing the unburned fuel to build up, do a fuel pressure test.

    Tee a gauge (100psi min.) into the line coming off the rear of the fuel rail. Turn key on and hit starter.
    Pressure should be around 38psi.




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    Lee Fulton Forum Moderator
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  3. #3
    A bozo on the bus deilenberger's Avatar
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    The fact that raw fuel came out of all the cylinders means there is a common factor at work. It's not a dripping injector since that wouldn't account for all four. It could be shorted wiring going to the injector - the injector received +12 V as long as the ignition is on. It is opened by grounding the other side of the coil, which is done by the L-Jetronic ECU. It is REALLY rare to have the L-Jetronic fail, but it should be fairly easy to check for if you have a Voltmeter.

    With all injectors unplugged - unplug the L-Jetronic brain. Turn on the ignition. Figure out which pin of the injectors is +12V by using your voltmeter in DC volts mode and checking for voltage - with the negative meter probe going to a bolt on the engine. If you see 12V - so far so good. Now measure across the injector plugs. You should read 0V.

    If you read other than 0V under these conditions, start searching for the problem in the wiring harness.

    If it passes this test (no voltage read across the injector plugs in the test above) - then turn the ignition off and plug the ECU back in. Turn the ignition on and repeat the same test. IF you then see 12V across the plugs (engine NOT running) the problem is in the ECU/L-Jetronic box. Luckily if that is the case, a used one should be rather cheap since they almost never fail.

    Good luck and let us know the outcome..
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  4. #4
    Registered User Sailingfool's Avatar
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    Thanks D! Life finally gave me a minute to look into this.

    In testing like you suggested, with the injectors unplugged, ECU unplugged, Ignition on, I found one pin connecter at 1V, all others 0V. Plugging the ECU back in, ignition on, checking across the injector plugs, there was 0V on all 4 injectors. Battery voltage was 12.3V.

    Should I take it to mean my problem is in the wiring harness somewhere, as I didn't get the 12V across the ECU plug?

    I appreciate your help!

  5. #5
    3 Red Bricks
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    No, it means that the ECU is not incorrectly telling the injectors to fire when they shouldn't. That's a good thing. It sounds like it might not be an electrical or computer problem with the fuel system.

    That would leave either no spark to fire the fuel or too much fuel pressure causing the mixture to be too rich to fire as the problem. Check for spark. Do a fuel pressure check.



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
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  6. #6
    Registered User Sailingfool's Avatar
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    I've got spark. Need to find a pressure gauge!

  7. #7
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    How do you know you have spark?

    I'm not saying you don't - I just don't see where that was established.

  8. #8
    Registered User Sailingfool's Avatar
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    Grounded a spark plug on the engine and cranked it, fire extinguisher near by. Observed the spark.

  9. #9
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    Make sure you try a plug on each of the two coils, just to be sure both coils are working.



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  10. #10
    Registered User Sailingfool's Avatar
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    It's starts!

    The wiring harness is very tough to trace! I'm amazed at all of the plug connectors that aren't connected to anything. I assume they are for LT options my RS doesn't have (stereo, heated grips, ect). At any rate rather than tracing each wire, I cleaned every connector and ground I could find, and reassembled the whole menagerie. Getting those tiny clips back on the injectors was really fun for a near blind fat fingered shade tree guy!

    So, not knowing if I fixed anything or not, it fired on the first try! Two rides later, it is hard starting when cold, and it appears to be running rich. How do I remedy rich running?

  11. #11
    3 Red Bricks
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    Rich is caused by too much fuel for the amount of air. Too much fuel on an injected motor is caused by too much pressure at the nozzle or too long of a squirt by the nozzle. Guess which one is easier to check. Check your fuel pressure.


    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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