K75 has no spark

Discussion in 'Road Warriors' started by KungPaoDog, Jun 30, 2012.

  1. KungPaoDog

    KungPaoDog Been here awhile

    Joined:
    Apr 17, 2010
    Oddometer:
    507
    Location:
    Colorado
    I just replaced the clutch and got it all closed up. It started and ran on the table before I took it all apart.
    Fuel pump and injectors seem to be doing their jobs. Turns over strong. No spark to be had.

    The coils seem to check out (~10k ohms)
    The coils seem to be getting power (~12v) and they seem to be getting signal when the engine is cranking.
    New plugs haven't helped.
    I doubt I managed to bugger up all 3 plug wires at the same time, but I guess it could have happened:huh

    I put dielectric grease on all electrical connections on reassembly. Is it possible for this to cause problems?

    I'm thinking I might have managed to somehow kill the EFI brain or one of its wires, but I don't think it talks much with the ECU that controls spark. And I never touched the ECU box.

    Any ideas? I'll buy the beer if you can bring over your K75 so I can swap and check parts.


    EDIT: I didn't replace the "guardian bell" that the PO had left attached to the bike. Will that cure my problems?:rofl
    #1
  2. duck

    duck Banned

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    Mar 19, 2004
    Oddometer:
    10,403
    Location:
    Seattle (Berkeley with rain)
    Did you remember to hook up the ground under the bottom of the #3 coil?
    #2
  3. jdiaz

    jdiaz .

    Joined:
    Feb 27, 2002
    Oddometer:
    32,325
    Location:
    Flyover State
    Is the ECU connector fully seated? Try unplugging/replugging again.
    #3
  4. KungPaoDog

    KungPaoDog Been here awhile

    Joined:
    Apr 17, 2010
    Oddometer:
    507
    Location:
    Colorado
    I did, but that was about the only thing I didn't label when I took it off. It is supposed to go between the number 3 coil and the coil mounting bracket, correct?

    Would it be worth extending that ground to a more solid ground point?
    #4
  5. KungPaoDog

    KungPaoDog Been here awhile

    Joined:
    Apr 17, 2010
    Oddometer:
    507
    Location:
    Colorado
    I did that a few times in hopes that it would clean the contacts a wee bit. I still haven't ruled it out since the bike will still turn over even if the ECU is completely disconnected. How do I test the ECU?
    #5
  6. duck

    duck Banned

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    Oddometer:
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    There should be a ground wire that comes out of the FI wiring harness with the three sets of coil wires.

    [​IMG]

    (Ignore the Posi-Tap. I added that for cruise control.)
    #6
  7. KungPaoDog

    KungPaoDog Been here awhile

    Joined:
    Apr 17, 2010
    Oddometer:
    507
    Location:
    Colorado
    Thanks for the pic. That's where I have mine. Triple cleaned, too.
    #7
  8. duck

    duck Banned

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    Mar 19, 2004
    Oddometer:
    10,403
    Location:
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    Try hooking up a VM to one of the black/(blue/green/red) wires and hitting the starter. Those are the wires from the L-Jetronic that tell the coils to fire. (According to the wiring diagram.)

    Wouldn't hurt to check/replace the #5 fuse - that powers the L-Jet.
    #8
  9. KungPaoDog

    KungPaoDog Been here awhile

    Joined:
    Apr 17, 2010
    Oddometer:
    507
    Location:
    Colorado
    Yep, I did that, too. All three coils get ~12v constant when the ignition is on, and the other wires going to them show voltage fluctuation when I hit the starter. Is there a number I should be able to read at the black/(blue/green/red) wires? I doubt that a VM has enough resolution to show anything useful. I don't think I have access to an oscilloscope.

    I checked the fuses and they all pass a visual inspection.

    Thanks for trying to help! I really need some right now.
    #9
  10. duck

    duck Banned

    Joined:
    Mar 19, 2004
    Oddometer:
    10,403
    Location:
    Seattle (Berkeley with rain)
    Try the VM on AC. I know you can get readings that way when the engine is running. Not sure when starting since it's slower.
    #10
  11. duck

    duck Banned

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    Oddometer:
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    If you suspect a blown L-Jet and want to try to find one to swap in then try posting on The Rockies regional forum here or maybe your local CL.
    #11
  12. KungPaoDog

    KungPaoDog Been here awhile

    Joined:
    Apr 17, 2010
    Oddometer:
    507
    Location:
    Colorado
    I get 12 mV DC on my multimeter when I read these wires, and nothing on AC:hmmmmm. Can you or any other K75 owner check what they get when they turn over their bike? Thanks in advance for any help.
    #12
  13. KungPaoDog

    KungPaoDog Been here awhile

    Joined:
    Apr 17, 2010
    Oddometer:
    507
    Location:
    Colorado
    In case anyone else has trouble with their K75, here's what I did:

    -New plug wires- It was driving me crazy that I couldn't verify if my old wires were good, so I ordered these.
    Still no spark, but at least I had known good wires:ddog

    -I built a LED tester for the hall sensors. Hall sensors were good. :baldy

    -I cleaned the starter and the starter connections. All seemed good, and no improvements.

    -I checked all the relays: starter, load shedding relay are the big ones for this system. All good, no spark.:bash

    -I traced all the wires between the hall sensors, coils, EFI brain box, ICU, ignition, etc. They were all good.:puke1

    -I pulled off the cluster of ground wires that attaches the the frame under the tank. All the grounds looked pretty good, but I scrubbed them all clean and put some dielectric grease on them (like everything electrical I've touched). Success!!

    So the moral of the story is that you should clean your connections before wasting money on testing and verifying parts if your K75 doesn't have spark:rofl

    I'm back on the road, baby:ricky
    #13