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Thread: Earthing of the ECM

  1. #1

    Earthing of the ECM

    Hi all
    I've been looking at the earthing of the wiring loom because I've got a random misfire and so many threads say that's the place to start.
    I've come across something strange and want a second opinion.
    My 07 Uly has 2 black wires from the black Deutsch plug on the ECM going to earth. They go to a single crimped lug that clamps to the cable from the battery negative inside the cast subframe.
    When I measure the resistance of just those 2 wires with a Fluke digital multimeter and a pin the right size pushed into either socket, I get a reading of 7.0 ohms +/- 0.1 on each one even though they're different sizes. I've checked with another meter and it confirms the high resistance.
    That size wires and that short a distance should have almost no resistance, 0.2 ohm at worst.
    Is this normal on a Buell? Could someone please check their wiring and see what it reads?
    I imagine that the ECM being at some voltage above earth might corrupt the information from the O2 and Engine temperature sensors since they both earth through the engine/frame.
    Comments pls
    Thanks - jv

  2. #2
    Senior Member
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    Did you remember to zero your meter, and are your connections clean ?

  3. #3
    Yep meter zero and connected to clean 1.4mm pin inserted into plug. Pretty sure it's reading properly.
    Because both wires read same it's got to be a bad crimp right?

  4. #4
    Senior Member lunaticfringe's Avatar
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    yes john that seems to be a correct assumption. i'll also mention this: i've owned probably 8 ulysses to date and every single one of them had a light throttle/low speed/moderate rpm cough or hiccup or misfire or stutter or pop or whatever you want to call it. the 2006-08 models i've owned were the worst offenders. what always resolved it? an installed generic race-map tune....fresh set of plug wires.....NGK DCPR9EIX (OR 8) plugs....and an auxilary ground wire.

  5. #5
    Thx Lunatic. I'd discovered the auxilliary ground wire which cured my misfire (I think) but then found the earth problem with the ECM. Can see the plugs and plug wires helping and will do. I have the std exhaust (and exhaust valve working now which had been wired open) - is the Buell race map advisable with this? Its richer low down is it? I have ECMdroid - jv

  6. #6
    Senior Member lunaticfringe's Avatar
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    Quote Originally Posted by John Vreede View Post
    Thx Lunatic. I'd discovered the auxilliary ground wire which cured my misfire (I think) but then found the earth problem with the ECM. Can see the plugs and plug wires helping and will do. I have the std exhaust (and exhaust valve working now which had been wired open) - is the Buell race map advisable with this? Its richer low down is it? I have ECMdroid - jv
    always my pleasure john. those sub-harness ecm grounds to inside of the frame rail critical. hoping that solves your problem. on the map john the one i was referring to is the generic ecmspy race map for 03-07 inclusive XB12 models. came with my ecmspy software i bought ions ago. i THINK it retains stock fuel mapping for cold start and open loop idle....then "richens" things up when in closed loop and off-idle throttle commences but don't quote me. i am NO ecm guru. half of my ulys' retained stock muffler and operational IEV system and this mapping worked nicely.

  7. #7
    Great. Forgot to say has a new std filter in too (was trying to get it to run well as std before trying anything else).
    The generic race maps still ok even though has no high flow filter?
    Will try the plugs and map when I get home in a week and report back then. Thx - jv

  8. #8
    Sorry its been a month. Got back to the bike after 3 weeks of late autumn bad weather.
    I implemented Lunatics recipe in stages to see what cured the misfire and found the following, riding it ~60 miles between changes:
    1. 99% of the misfires ceased when I put in an earth from the battery -ve to all the other earth points (forward one inside frame rail looped to the back one, braid at the dogbone on upper frame, under fixing bolt for coil and on the front of the frame by the steering head)
    2. Richened the mixture in stages with EcmDroid. Last of misfire gone when I locked the AFV at 107-109% (before started AFV was 102.2%), so presume it was a lean stumble. No improvement going from std to 105% then dramatic improvement in ride-ability as well as misfire gone at 107%, couldn't tell the difference between 107% and 109%
    3. Plug wires made no difference to my bike (not saying that it isn't good to do, just that I couldn't tell the difference)
    4. Ditto sparkplugs (Iridiums are equivalent of $30US each in NZ - plug wires were cheaper)
    Haven't dealt to the high resistance crimp yet. Whatever it doesn't seem to be implicated in the misfire problem.
    Really appreciate your help - jv

    Edit: I originally found the high resistance crimp with my $10 DMM (measured 4 Ohms). I wondered if I'd measured right or it was accurate enough, so borrowed a $1000 Fluke DMM. Result was even higher resistance (the 7 Ohm above). After reassembling with CRC2.26, I measured over a period of weeks with the cheap DMM and kept getting lower (but not near-zero) resistances each time I measured, so got an electrician with a Fluke meter to measure again and now the resistance of the crimp is the same as touching the probes together (0.1 Ohm - where it should be). The high resistance didn't ever seem to be part of my misfire problem, though you'd expect it to be an issue. Poor original measuring or bad crimp fixed by CRC 2.26 'improv(ing) the electrical properties' - who knows? I won't be changing the crimped lug - just yet.


    Last edited by John Vreede; 07-30-2018 at 09:13 AM. Reason: New info

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