Results 1 to 15 of 62

Thread: 1990 K75S died suddenly

Hybrid View

  1. #1
    Registered User jwetering's Avatar
    Join Date
    Aug 2011
    Location
    north vancouver
    Posts
    156

    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
    Join Date
    Apr 2011
    Location
    Rocky River Ohio
    Posts
    51
    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
    Join Date
    Aug 2011
    Location
    north vancouver
    Posts
    156
    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
    Join Date
    Mar 2003
    Location
    Spring Lake NJ, USA
    Posts
    7,748
    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
    Join Date
    Aug 2011
    Location
    north vancouver
    Posts
    156
    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.
    Attached Images Attached Images
    jasper
    north vancouver

    1990 K75S

  6. #6
    3 Red Bricks
    Join Date
    Jan 2007
    Location
    Pleasanton, Ca.
    Posts
    3,425
    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

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •