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Thread: 1990 K75S died suddenly

  1. #1
    Registered User jwetering's Avatar
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    1990 K75S died suddenly

    Here's the story - please help me diagnose my fault.


    1) The bike has been running like a champ since I put it back on the road on January 1st. No operating issues whatsoever at any speed or under different loads.

    2) I've been riding the bike every day now for two weeks. My commute is 25 miles each way. No problem.

    3) Yesterday I rode with my mates to a bike show 25 miles from my house.

    4) On the way home it faltered once. The stumble was short - so short I almost missed it. It did not happen again that day even though I rode for another 30 miles in another direction (went to check out a bike with my Ducati riding buddy).

    5) Rode the bike to work this morning as usual.

    6) On the ride home - I had traveled about a mile and the bike dies. No partial power - dead. Roll to a stop on the side of the road.

    7) It felt like I hit the kill switch - but I didn't and the lights on the dash were on.

    8) I turned everything off - then back on and tried again. Lights are all on - and it turns over normally.

    9) No start - No pops - no rumbles, no anything except kee-kee-kee-kee-ka-whirrrrrr as I let my finger off the start button.

    10) I unplug the computer seems tight. Plug it back in - goes together well - try again - no joy.

    11) At that point I push it the one mile back to work and park it. My buddy was ready to give me a ride home so I didn't spend anymore time on it.

    12) While I was waiting for him to get the car I tried turning it over a few times and smelled for raw fuel at the tailpipe. Not a great test - but I didn't smell a thing.

    So tomorrow I will check for spark using an ignition tester (the brass gap type of device). Assuming I see a spark - what should I check first on the fuel system - power to the pump I suppose. How do I best go about that? (I have a multimeter and know how to use it).

    I'm kind of gut-thinking my computer may be toast. Do the systems I describe support that? How does one go about testing the computer?

    How do I best test for fuel flow while cranking?


    Thanks for any help gents.
    jasper
    north vancouver

    1990 K75S

  2. #2
    K75RT Keith
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    I'll ask the obvious question first. Is there gas in the tank?
    You should hear the whir of the fuel pump when you hit the starter button, but if you smell gas,I doubt the pump is out. Check the connector for the fuel pump if you don't hear the pump.
    Possibly the Hall effect Sensor failed.

  3. #3
    Registered User jwetering's Avatar
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    Quote Originally Posted by KKELLER149854 View Post
    I'll ask the obvious question first. Is there gas in the tank?
    You should hear the whir of the fuel pump when you hit the starter button, but if you smell gas,I doubt the pump is out. Check the connector for the fuel pump if you don't hear the pump.
    Possibly the Hall effect Sensor failed.
    Thanks KK

    1) I'm sure it's not out of fuel. The low fuel light didn't come on, My odometer only shows 116 miles, and it stumbled yesterday already once. Also - nit died suddenly. If it was out of fuel it would have stumbled.

    2) I didn't smell gas - but I will listen for the whirr of the pump. Where is the connector for the fuel pump located? Question: does the computer cotnrol the pump???

    Thanks guys - keep the tips coming!
    jasper
    north vancouver

    1990 K75S

  4. #4
    A bozo on the bus deilenberger's Avatar
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    I love numbered paragraphs!

    1. OK, so there is fuel in the tank.

    Have you pulled the plugs - that's a quick way to determine if the engine is getting fuel. If the plugs are wet, chances are good there is fuel being injected.

    2. The connector is at the right (starboard) lower corner of the tank. It goes into the float-level assembly. It's on a pig-tail. And yes - the computer controls the pump.

    A thought..

    An engine needs 5 things to fire:
    1. Fuel
    2. Oxygen
    3. Compression
    4. Ignition
    5. A place for the waste product of combustion to go.

    I'd look at that list and think a bit about how to determine what's missing.

    Fuel - look at the plugs. If they're wet - there is fuel, and chances are good #4 is missing - no ignition.

    If the plugs are dry - then I'd look at the fuel system, starting with pulling out the plugs for the injectors and see if you get a constant 12V on one side of the plug with the key on (the injectors are fired by grounding the other side through the ECU.)

    While the plugs are out, good time to check for compression - but chances of losing it in a 3 cylinders at once are slim to none.

    We'll assume the air intake is clear and nothing is stuffed up the exhaust pipe (it's happened..)

    So - diagnostic steps, before chasing demons:

    1. Pull plugs.
    2. Report back on the appearance of them. (Wet/Dry)?
    3. If wet - put 2 back, then put one in it's connector and very carefully ground the shell so you don't have to hold it to ground it.. then crank the engine. Is there spark?
    4. If dry - have you checked all the fuses? (Sometimes it IS the simple things..)

    We can go from there. While it certainly could be a HES failing, it's an expensive item to troubleshoot by replacement, I'd want more confirmation it's faulty before considering replacing it.
    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

  5. #5
    Registered User jwetering's Avatar
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    Good stuff Don. Thanks for the tips. We're on the same page. The tailpipe and inlet are clear. This isn't my first rodeo The bike has been running like a champ for months now and I maintain it to an (ahem) high level of tune.


    Here's my plan.

    step 1) Test for sparks using my ignition tester (see the photo).

    If spark then:

    step 2) Test for 12V at the injectors.

    If power at the injectors then:

    step 3) pull the plugs to check if they're wet or check for power at the fuel pump - or both.

    If power at the fuel pump and the plugs are wet then it must be ignition.


    If there is no spark at step 1 however then what? I'd like to check for power to the computer - is there a procedure for doing that? I'll still check for fuel as well - if there's no spark and no fuel then we look at the computer - or the power to it.


    Also - I checked all of the fuses on the fuse block next to the ignition coils already (forgot to list that in my OP) - they all look good, but they are labelled in German and while I can make out which fuses control the the headlights and signals, it's not obvious which one(s) control fuel or spark (or computer). Is there another fuse block somewhere on the bike?

    It's a bit moot because they all look good but weird things can happen.


    Also - it stumbled yesterday, then ran fine for another 50 miles. Fuses don't normally behave that way.


    Couple of major points:

    1) the bike is 25 miles away at the moment so I can't check anything until after work tomorrow.

    2) I have a Clymer\ manual, I'm just going to tuck into that now.


    Thanks a million for your help !






    Quote Originally Posted by deilenberger View Post
    I love numbered paragraphs!

    1. OK, so there is fuel in the tank.

    Have you pulled the plugs - that's a quick way to determine if the engine is getting fuel. If the plugs are wet, chances are good there is fuel being injected.

    2. The connector is at the right (starboard) lower corner of the tank. It goes into the float-level assembly. It's on a pig-tail. And yes - the computer controls the pump.

    A thought..

    An engine needs 5 things to fire:
    1. Fuel
    2. Oxygen
    3. Compression
    4. Ignition
    5. A place for the waste product of combustion to go.

    I'd look at that list and think a bit about how to determine what's missing.

    Fuel - look at the plugs. If they're wet - there is fuel, and chances are good #4 is missing - no ignition.

    If the plugs are dry - then I'd look at the fuel system, starting with pulling out the plugs for the injectors and see if you get a constant 12V on one side of the plug with the key on (the injectors are fired by grounding the other side through the ECU.)

    While the plugs are out, good time to check for compression - but chances of losing it in a 3 cylinders at once are slim to none.

    We'll assume the air intake is clear and nothing is stuffed up the exhaust pipe (it's happened..)

    So - diagnostic steps, before chasing demons:

    1. Pull plugs.
    2. Report back on the appearance of them. (Wet/Dry)?
    3. If wet - put 2 back, then put one in it's connector and very carefully ground the shell so you don't have to hold it to ground it.. then crank the engine. Is there spark?
    4. If dry - have you checked all the fuses? (Sometimes it IS the simple things..)

    We can go from there. While it certainly could be a HES failing, it's an expensive item to troubleshoot by replacement, I'd want more confirmation it's faulty before considering replacing it.
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    jasper
    north vancouver

    1990 K75S

  6. #6
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    Jasper,

    When you get back to the bike, try once or twice to start it. IF it starts, it is possible that the Hall Effect Sensor MAY be going bad (when starting to go bad, it can be heat sensitive). If no start, continue with Don's suggestions.

    If still nothing is obvious, try thoroughly cleaning and drying and regapping (or replacing) the plugs.

    If still nothing follow this:

    http://www.bmwmoa.org/forum/showthre...it-won-t-start




    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  7. #7
    Registered User jwetering's Avatar
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    Good morning Lee!

    Thanks for checking in.

    In fact about 15 minutes ago - the following happened.

    1) Got to the bike, pulled plug wire #3 and tried to insert my ignition tester but the endcap on the wire was too deep.

    2) I pulled plug #3 - grounded it against the bike and cranked it over.

    3) Nice big spark AND the bike started to run - on 2 cylinders of course.

    4) Shut it down - replaced the plug - started the bike and it ran fine...for about 4 minutes...then it stopped.

    5) Pulled plug #3 again - no spark at all.

    6) Pulled plug #2 and I wouldn't say it was wet...but I do think I smelled fuel in the fog that came out of the spark plug holes while I cranked.

    It didn't get real hot in the 4 minutes that it ran - and I haven't confirmed fuel 100% yet. But I will check again at lunch.


    In the meantime - I will price out a hall effect sensor !

    cheers


    Quote Originally Posted by 98lee View Post
    Jasper,

    When you get back to the bike, try once or twice to start it. IF it starts, it is possible that the Hall Effect Sensor MAY be going bad (when starting to go bad, it can be heat sensitive). If no start, continue with Don's suggestions.

    If still nothing is obvious, try thoroughly cleaning and drying and regapping (or replacing) the plugs.

    If still nothing follow this:

    http://www.bmwmoa.org/forum/showthre...it-won-t-start




    Last edited by jwetering; 04-30-2013 at 03:15 PM.
    jasper
    north vancouver

    1990 K75S

  8. #8
    Registered User jwetering's Avatar
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    So new hall effect sensor plates are available on-line for $379 from a few different sources. The thread that Lee referenced includes a procedure for testing the sensors as well.

    Interesting though that the sensors themselves used to be available from Honeywell for $20 each - part 2AV54 - but these have been obsolete since about last year. A replacement part has popped up - the so called BBHME56 - but these are $60 each.

    I have a little more testing to do before I spring $379 for a new plate - up to and including testing the sensors that are installed now. Depending on what my testing shows - I *might* cheap out and but two new sensors for $120 and rebuild my old plate - but so far I haven't found anyone who has done this successfully (as opposed to quite a few success stories using the 2AV54).

    Note that the sensors themselves were used on a huge range of BMW motorcycles - although each plate is different.

    One more big question here....there are two sensors and common sense says they won't both fail at exactly the same time. Shouldn't the bike run lumpy with one bad sensor? Why are there two sensors for a 3 cylinder bike? I can see it on a 4 cylinder - which uses a "wasted spark" where two cylinders spark at the same time even though one is on the exhaust stroke - but I don't get exactly how it works on a 3 cylinder.


    Anyone??
    jasper
    north vancouver

    1990 K75S

  9. #9
    Registered User jwetering's Avatar
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    Just went out on my coffee break and tried the bike.

    It started right up and kept running to the point of being fully warmed up (choke off - 1000 rpm idle)

    I ran a circle or two around the parking lot and shut it down.

    It's going to be awful hard to troubleshoot any further if it keeps running normally.

    I think I will take out the hall sensor plate and do the electrical test cold and again after I heat it up with a hair dryer.



    Can someone explain exactly how these two sensors fire three cylinders?

    There are two sensors on the plate 120 degrees apart, and two magnets on the shaft, also 120 degrees apart.

    I see a signal when magnet 1 passes the first sensor, another signal (actually two simultaneous signals) when magnet 1 passes the second sensor and magnet 2 passes the first sensor, and a third signal when magnet 2 passes the second sensor.

    That's three signals 60 degrees apart but I still believe that both sensors started failing at the same time - so why is the bike dying rather than missing?

    Thanks gents.
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    jasper
    north vancouver

    1990 K75S

  10. #10
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    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  11. #11
    Registered User jwetering's Avatar
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    Thanks Lee - I've removed the tank in preparation for removing the HES.

    I now have to decide if I should reassemble the bike so I can ride it to an electrical outlet where I can test the HES with a heat gun.

    Probably wouldn't be a bad idea.

    Then again - replacing the HES at this point might be a good preventative measure. If it isn't the problem now - it probably will be in the future.
    jasper
    north vancouver

    1990 K75S

  12. #12
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    Intermittent Engine Miss

    I had an intermittent miss in my '87 K100RT about 10 years a go. It evolved into just dying and not running. Drove me nuts. When it ran everthing seemed to check good. It would run, then not run. It drove me crazy, I couldn'nt depend on the bike. Got the bike running, lifted the tank up at the backand blocked it up. Stated checking the sending unit coming out of the bottom of the tank. Appeared good by looks. Started moving the wiring harness around, kinda jiggleing it. The bike died. The unit was bad.
    The problem was in the plastic pod attached to the square metal unit that bolted into the bottom of the tank. The pod housed the wires for the pump and float. It wasn't repairable by me. Installed a new unit, problem solved. This could be your problem. Good luck getting your bike fixed.

  13. #13
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    Jasper,

    I would be hesitant to start throwing parts at it, especially expensive parts until tests confirm what the problem really is.

    As it stands, you still don't know if it's an intermittent ignition problem or an intermittent fuel/pump problem. All you KNOW is that it is intermittent. There are several possibilities. Most of them are electrical and require patience and organized troubleshooting.

    Read:

    http://www.k11og.org/forum/viewtopic.php?t=8412 EDIT: Just saw Barry's post. This describes one person's quite long attempt to find that exact problem.

    I've seen this problem on a couple of K75s also as they share the same tank wiring. Could be the connector, could be the sender plate.

    Intermittent problems are tough. You need to get the bike home where you can do your troubleshooting.



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  14. #14
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    Yea, I'm not sayin to go buy a sending unit. Just if all else fails and a solution isn't forthcoming, it's just something else to check to get the bike fixxed and on the road and be dependable.

  15. #15
    Registered User jwetering's Avatar
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    Well ain't that a bitch.

    I built myself a super slick test rig with a 12V power supply, an LED with a 1000 ohm resistor in line, and crimp on spade connectors. A pretty nice job if I do say so myself.

    ....and both sensors test normal at 20 degrees C and at 126 degrees C. (the photo shows 114 C but trust me it got up there).

    It doesn't seem like the HES is my problem.

    I guess it's a trip through intermittent hell for me.

    Step 1 - clean all of the connections - most notably the ignition control box.

    Step 2 - I'm stumped.

    Looking at Don's list of items to check (in the link that Lee posted) - he seems to be addressing a high speed stumble as well as an intermittent cut-out. I'm not experiencing any operating problems at all.


    Any other tips guys? Don?

    thx
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    jasper
    north vancouver

    1990 K75S

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