2008 XB12XT Poor Idle & Backfire

[steve92106]

I went out for another look and to do the TPS reset just now. When I looked really hard at the ECM I noticed very fine cracks in the rubber case at juncture with the forwardmost of the two multiplex connectors. It looks as though maybe the seat has been putting pressure on the connector itself and the hard rubber casing material has fatigued. When I pushed down on the connector I saw the cracks widen a bit. Could this be causing my problems? The bike runs fine until I get it home from a long (150-200 mile) ride then the idle goes to crap and the CEL illuminates. Would applying some silicone sealant over the cracked rubber be a good idea?

[BuellyBagger]

@steve: I suggest getting the bike warmed up and do a little "wiggle" testing while its idling. Give the connector on the ECM a good shake and tug (don't try to rip them out or break them just try to move em). If your CEL comes on when u begin the wiggle test (or ur idle goes to crap) you may have just found your issue. I had an ECM go bad in my ULY a year ago with no warning and no apparent damage. It thru TPS trouble code which I promptly shot from the hip and replaced (to no avail) and then I got a service manual and actually went thru the steps of diagnosing it. Came down to the ECM. So I got an EBR one (set up for my exhaust) and so far for 1.2 riding seasons, she's all good (knock on wood)

[steve92106]

Buelly, Many thanks for the suggestion. I'll take a stab at that. Even if it doesn't confirm a problem, I think I'm going to cut away some of the seat shell and make sure it can't put any more pressure on the part. I think I'll also use the sealant. Even if it's not the source of the problem, it can't be good to have those cracks.

[steve92106]

Post Mortem: After not getting any reaction to BuellyBagger's wiggle test, I did seal up the ECM and ride the bike again. Again, after a short (100 mile) ride the idle started doing it's possessed by demons thing. So, regretfully, I took it into the HD dealer for a diagnostic and was told yesterday the immediate culprit is the "idle air motor". I have no idea what that is but it's an estimated $315 fix which seems like a bargain considering what I was afraid of hearing. The tech also recommended replacing the ECM since the the harness can be moved when the plugs are wiggled. I figured since the problem only occurs at idle and since there were no error codes indicating a bad ECM, I would just wait. The factory ECM is over $500 before the cost of a new download! It may come to that but I don't see any sense in dropping that kind of money until it's confirmed. The EBR ECM isn't legal in CA and they've been getting pretty sticky about that. Only good thing about waiting for the part is I get to rent a Fat Bob for cheap and I've been wanting to test ride one for months.

[steve92106]

Next Chapter in My Little Saga: After paying for the idle air motor plus another $95 for the diagnosis (I always thought a diagnostic charge came off the repair bill, what happened there?) I rode it to work on Thursday. On the way home I "diverted" to a little twisty back road and was just exiting to the freeway interchange twenty minutes later when the CEL light came back on. Now the dealer has it again. I guess they've had a number of conversations with HD with no brilliant ideas to date. It's probably a good thing I don't have the money to buy another bike.

[steve92106]

Well, almost $1100 later the shop claims it's solved the problem with a new ECU.