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Thread: false check engine light

  1. #1
    Junior Member
    Join Date
    Dec 2011
    Posts
    10
    long story. 2006 uly with 20k. drummer installed. about two years ago at higher speeds - usually 70+, and warmer temps - generally over 60f, I would occasionally feel the engine stumble and notice the cel is flashing - feels and looks like it goes into spark skip mode. usually backing off the speed 4-5 mph would resume normal ops. then after a few more minutes it would happen again - back off another few mph and it'd recover. for a few minutes. repeat the cycle until i finally stop, let it cool. then it may or may not happen again on the rest of the ride. i jumpered the pins after the ride - no engine trouble codes. on another forum i heard someone had similar issues and solved it by ward-wring the fan to a toggle switch. the reason was he had heard it was voltage fluctuations in the fan feeding back through the ecm via the path to ground, and the hard-wring to a toggle switch with a direct ground cured it. not wanting to have the fan on all the time , i put in a three position fan with a variation. position 1, normal power feed, normal ground. position 2, interrupt the circuit to the fan. i don't remember if it has power with no ground, or ground with no power. position 3, normal power with a new direct return to ground ( not through the ecm. My thinking was this - position 1 - normal ops. stay there unless i had a problem. position 2 - no fan at all - mostly to test the theory it was the ground through the ecm that was causing the problem. position 3 - i would switch to this if it was hot enough to need the fan but since it avoided grounding through the ecm, it should avoid the spark-skip and stumble. the only issue with position 2 was that the cel would come on steady. the bike would run fine but i worried about over heating. jumping the pins after the ride showed no engine codes. i thought it was working - until today. took a 125 mile ride yesterday and sure enough, 30 minutes into the ride on the highway it went into the false spark-skip. tried position 2 just for fun - no issues but also no cel (unusual) went to position 3 - ran fine. coming back today in a fine rain, 30 minutes in false spark-skip. right to position 3 - no issues. then it went into spark-skip. first time that ever happened. got progressively worse, kept happening no matter what position. then cel came on and stayed on. pulled over, let it cool 15 minutes. back on the highway, low fuel light came on. filled up, got back on the highway. pretty pissed now so i ran it hard for 30 minutes in position 1. no issues. WTF? the rain maybe shorting the toggle switch or something else? i had mentioned the whole thing to a friend between the two trip legs (power production guy who used to have a firebolt) and he thinks there is a bad bimetallic disk on the rear head (part of the temp sensor) that has gone bad and is arcing when the engine get hot. this would explain why it never happened for the first few years of the bikes life. i don't even know if it has such a disc. i am ready to just hard-wire the fan on a two position switch and see what happens. the problem is that since it doesn't happen every ride, under seemingly similar conditions, it'll take a while to prove or disprove the theory. bottom line is this is affecting my riding because i'm afraid i'll get stranded someday. any ideas?

  2. #2
    Senior Member
    Join Date
    Aug 2009
    Posts
    1,344
    make sure ur battery cables are tight; if at 60mph the vehicle vibration can rattle the battery cables it will lose connection for a split second or two. and this will result in CEL, headlights dimming and engine sputtering too

  3. #3
    Junior Member
    Join Date
    Dec 2011
    Posts
    10
    thanks. checked before but i checked again just to make sure.

  4. #4
    Senior Member
    Join Date
    Aug 2009
    Posts
    1,344
    if anything post up a diagram, to the "T", of ur fan switch and let us help u diagnose that. faulty temp sensor could be the culprit along with a faulty coil, this would explain hot temp sputtering and loss of power



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