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Thread: Spastic tach

  1. #11
    Senior Member mmcn49's Avatar
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    I've had a similar problem for the past couple years. I've checked the wiring but have not done any real troubleshooting.

    If the issue is in the ECM, is it likely to fail completely or is the problem isolated to the pink wire solder connection?

  2. #12
    Senior Member Cooter's Avatar
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    I massively doubt its the ECM, you said yourself the datalog (what the ECM is seeing and logging) reads OK.
    If you are asking if something half-broken and limping along, will eventually fail? Then yes, whatever is broken now... won't get better, unless you fix it or break out the Ouiji board.

  3. #13
    Senior Member mriulvr's Avatar
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    Which leads me to believe (using your info) that you should remove the gauge cluster, carefully check that connector at the pink wire pin, and trace that on the SMC board to the stepper. Look for bad solder joints because it sounds like a temp driven loose connection.
    Removed the gauge cluster and did ^^^. Did a visual inspection but no bad solder joints visible as far as I could tell. Checked continuity along SMC board from pink wire pin to stepper motor and no issues popped up. Rechecked wiring behind windscreen and recleaned pins and connector before reinstalling. Still bouncing.

    Starting to think it is the stepper motor itself. I recall a post that I think was about replacing the stepper motor that Cooter either posted or commented on, surprising I know. Looked like pretty good soldering skills needed and I do not recall a part number for the stepper motor.

    Now trying to decide if I can live with the annoyance, tackle replacing the stepper motor, or replace the gauge cluster. Think I will go for a ride and ponder the existential delima.

  4. #14
    Senior Member mriulvr's Avatar
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    Update. Have not been on the Buell since late last fall. Have started her up regularly to keep her from feeling totally rejected. Got the COVID at end of January and it really kicked my butt for about 6 months and the heat this summer in TX was brutal. Finally took her out a couple weeks ago. Less than 2 miles on the way to get gas she dies. Hit ignition switch and no response. Turn her completely off and back on, flip switch, fuel pump runs, hit ignition switch, starts right back up. Get gas, pull out same thing happens again. Screw it. Head home. Check codes and nothing. Also, the tach was still its spastic self, fine at idle and low rpm but around 2700 RPM acts like a three year old boy who found the chocolate stash and washed it down with a triple espresso.

    Started with the wiggle test at the ECM and was able to duplicate but not consistently. Finally was able to narrow it down to either the front injector control and/or front coil control wire. I did notice some very slight insulation wear on a couple of wires that I wrapped and will do a better repair with shrink wrap later. Unplugged the connector and did a visual inspection (again) and again no sign of corrosion or damage. Sprayed male and female parts liberally with CRC Electric cleaner and reassembled. Same issue.

    Repeated above but took connector apart to inspect wire connections, which had no signs of wear or damage and all the male and female connections where clean. I was actually surprised how clean they were in an 18 year old 50k+ mile bike. Before reassembling the connector I used a drill bit smaller than the inner diameter of the female connectors and the CRC cleaner and did a gentle clean of inside of tubes. Reassembled plug, plugged back in, double checked seat clearance, and went for a ride. No dying. Only one ride so not convinced wether this issue is “fixed” or not.

    Hmm, made me wonder about the pink wire and spastic tach. Repeated what I did for the front injector and coil control wires with the pink tach wire. Also unplugged the cluster and did a liberal spraying of CRC cleaner and added a tiny bit of dialectic grease for the pink wire. Only done one test since but no spastic tach. Again, Only one ride so not convinced wether this issue is “fixed” or not.

    Seems like the issue is in the electrical flow between the male-female connections (I can almost hear the multitude of deranged replies).

    Also got me wondering if this could be happening, even intermittently, for other wires in either connector, if ECM itself has issues, or if the wire harness has worn spots somewhere. I hate going for a ride and not being confident that she won’t leave me stranded or die in the midst of heavy traffic. That lead to considering a couple of preventative measures
    - Send my ECM to IDS to get checked and if issues, then replace
    - replace the wire harness, (do these often need replaced? How difficult is doing this? Am I overreacting?)

    So, any sage insights or thoughts on next steps? Grounding points have been checked and cleaned.

  5. #15
    Senior Member Cooter's Avatar
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    If the stepper motor is intermittently bad or is losing power/ground supply on the PC board the needle won't "bounce". It will just freeze in place until it regains that intermittent power issue and will read proper RPM.

    If the cluster is losing power (pink wire or ground issue) both needles (speedo and tach) will sweep the full range, settle on zero, and then read normally after power is restored, just like cycling the key with the run switch on.

    If neither of those describe whats happening, then please post a video. Does it do it warm, above 3k rpm, in the driveway (not riding)?

    If the bike runs ok, the ECM is OK.

    If the bike runs OK, the wiring to the coils is OK.

    Dying and not re-starting is a completely separate issue. IMO, pull the right side handlebar controls apart and clean the contacts very well, or replace it. They will commonly corrode after sitting for extended periods. Clean the key switch contacts as well as the IGN relay terminals. Next time it happens, leave everything as it is and wiggle stuff until you hear the fuel pump run, then thats your issue.

  6. #16
    Senior Member 34nineteen's Avatar
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    To diagnose the spastic tach, this is what I would do. Remove the pin/wire from the ecm plug and wrap with electrical tape.

    You should have no tach function. This wire appears to only drive the tach on the speedo. If you still have a spastic tach, the problem is in the cluster. If you get nothing, the problem is either in the wire or the ECM. Next, I would run a separate wire from the ECM to the cluster for the tach signal. If this solves your problem, you likely only had a flakey wire, if not then you probably have an ECM getting weird.

    Some ECM's have shown weird things as they age, even though they dont show a code or create running problems.


    I included the wire diagram and instructions on how to remove it without damage. BTW, you dont need a the "special tool" to remove the pin. An awl or small screwdriver will do the trick.

    b1.JPG

    b2.JPG

    PS. CoOter is a spastic tach.



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