'03 XB9R Idle Problem

[audiowize]

Hello everybody,

I've been lurking around for a long time, and finally found myself a decent '03 XB9R with 8500 miles to add to the collection in my garage.

I've been working through the issues it has, including a decent number of chafed wires, a primary chain that was insanely loose, some unusual modifications to the wiring harness, and a TPS with a dead spot.

When I got the bike, and still persisting today, I can start the bike up and it idles wonderfully (especially after the TPS reset) and rides nicely. The issue I have is that about 5-10 seconds after the cooling fan comes on, the idle gets erratic and the bike dies. I had initially thought that I might have an intake boot leak, but the bike is neither reactive to propane nor ether sprayed around those gaskets. I have further convinced myself that an intake leak isn't the issue by repeatedly firing up the bike and observing it die when the cooling fan comes on.

Can anyone point me in the direction of proper diagnosis? Should I be looking at the data from the head temp sensor(s) in ECMspy? A Google search didn't turn up a lot of possibilities.

Thanks in advance for the help!

-Paul

 

[audiowize]

Today I continued working on this problem. I noticed initially that the voltage reported by EcmSpy seems to drop when the fan kicks on, so I replaced the connector from the R/R to the battery. To further check, I noted a bit of a difference in voltage between what the ECU was reporting and what the battery actually measured.

To correct this, I checked on the ground connections around the ECM, and indeed on of them seemed to be a little buggered.

I cycled through a few more tests, and now I'm noticing that when the fan comes on, the ECU stops reporting to EcmSpy. I also measured the current draw of the fan to be about 4.8 amps, which isn't abnormal.

At the moment, I'm considering getting the scope out to see if there's some weird junk riding on the DC rail of the bike from a flaky R/R.

 

[audiowize]

Well, I finally figured out the issue. With the voltage differential between ECM and battery, I started poking around measuring the various grounds on the bike. I then got back to the ground connection I had repaired and realized that it's on the triple tree clamp, insulated from the frame by the steering bearings! My DVM measured 0.5 Ohms of extra DCR, which may have been OK until the fans demanded that 4-5A of current was sunk through that interface!

I grabbed some 12GA wire from a neighbor's wire stash and ran an extra ground wire up from the battery ground next to the wiring loom and connected it with those two grounds on the triple clamp. I can now warm the bike up and cycle the fan with perfectly consistent idle.

 

[Cooter]

Boom.
Thanks for the report. Check yo' grounds people!!

 

[audiowize]

This is more of an issue with how the bike was made. Relying on the steering stem bearings to provide an adequate ground path for 5A of current is just asking for trouble. On other bikes I have, the steering stem tube has threaded bosses for these connections, or there is a wired ground buss that doesn't rely on the chassis at all for grounding.

 

[Cooter]

They don't actually depend on the steering bearings as a ground path as you reported, but I'm glad you found your problem.

 

[audiowize]

My Ecm grounds to the triple tree clamp, I don't see another path from there to ground other than the steering stem bearings. Am I missing a connection?