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Buell Forum » Big, Bad & Dirty (Buell XB12X Ulysses Adventure Board) » Archive through October 09, 2015 » Occasional Miss Under Acceleration « Previous Next »

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Hughlysses
Posted on Friday, July 31, 2015 - 02:25 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I spent 8 days riding around Little Switzerland, NC last week, the site of some really good roads. Just before the trip and when I was there, I noticed my Uly has developed an occasional miss under acceleration. In the mountains, it almost always happened when I'd get back on the throttle after a few seconds of no throttle, like when I was accelerating out of a turn. It was just like one cylinder missed firing once or twice. Other than that, the bike performed great, and would accelerate hard with no missing under most circumstances.

I know my plug wires are getting a little wonky. The slightest rain will cause the bike to miss under acceleration, so I'm kind of leaning towards the plug wires being the culprit. The other possibilities that occur to me are leaky intake seals (maybe the air leak under deceleration throws off the FI causing a miss when I get back on the throttle), or a bad TPS.

Anybody had something similar? I figure I'll install a set of plug wires and use WD-40 to check the intake seals and proceed from there.
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Readyxb
Posted on Friday, July 31, 2015 - 02:59 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Does it feel like a complete but momentary drop in power, as if the ignition were turned off and back on?

A data log might reveal the culprit for your issue. A TPS issue would be very obvious in a log.

I have seen few other threads about this type of behavior. One in particular I remember was a chaffed harness wire that only contacted the frame under acceleration, but moved away once the g-forces were gone. Could have been for a sensor, ignition switch... something along those lines.

If you had leaking intake seals, I would expect more than just one or two occasional misses only under acceleration, but performing the test is a good sanity check.
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Hughlysses
Posted on Friday, July 31, 2015 - 03:15 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

It's definitely a cylinder misfire, not a complete loss of power.

I did have a problem with a chaffed wiring harness a couple of months after I swapped engines (my bike's an 07 with an 09 engine) a few years back. The leads to one injector rubbed through and would short against a tab on the frame under the airbox resulting in a skip. Before, it would happen when I accelerated at cruising speed, and would happen EVERY time, but it's worth checking again. I taped up the wires then and put a section of ~1/2" hose over the tab when the problem first occurred so it's possible something's gotten out of place or rubbed through again.

I think you're probably right about the intake seals but like you say, it makes sense to check them.
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Tootal
Posted on Sunday, August 02, 2015 - 06:16 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I don't think it's seals, they don't do momentary issues. More of a constant problem. I think you're right, it's plug wires. I raised my coil up and ran the front wire between the throttle cables and it also took some slack out so it doesn't rub the frame/gas tank.
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Hughlysses
Posted on Tuesday, August 04, 2015 - 03:51 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I ordered new plug wires last night from Iron Machine on ebay (because I had a ~$40 PayPal credit burning a hole in my pocket). Hopefully that'll cure my problem.
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