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Old 08-21-2013, 04:46 AM   #16
Hughlysses
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Quote:
Originally Posted by Mr. Canoehead View Post
You could do the same with a relay, if there isn't one already (that would be surprising).

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The electrical system has a relay for the fan; the problem is apparently with the wiring harness or the internal circuitry of the ECM on the particular Uly that's being referrenced. The owner tried everything he could to eliminate the problem until in desparation, he wired a manual switch in to the relay that controls the fan. This switch grounds the wire from the relay that normally goes through the ECM. Apparently what was happening was that the small current required to close the relay for the fan was sufficient to cause "wonkiness" with the ECM. It's definitely a work-around fix, but it was simple and has proved relaible.

I still think it's worthwhile to verify that the grounds in the tail section are good. If the ECM isn't grounded properly, it can cause really odd issues like this. Mr. Canoehead- your description of the operation of the sensor is obviously correct, however I think that a problem with the ECM grounding can result in it mis-reading the signal from the sensor. Excessive resistance in the ECM ground may mimic low resistance in the sensor.

If the bike is actually going into skip spark, it should display a check engine light (flashing IIRC) while it's happening.
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Old 08-21-2013, 09:04 AM   #17
Mr. Canoehead
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Quote:
Originally Posted by Hughlysses View Post
The electrical system has a relay for the fan; the problem is apparently with the wiring harness or the internal circuitry of the ECM on the particular Uly that's being referrenced. The owner tried everything he could to eliminate the problem until in desparation, he wired a manual switch in to the relay that controls the fan. This switch grounds the wire from the relay that normally goes through the ECM. Apparently what was happening was that the small current required to close the relay for the fan was sufficient to cause "wonkiness" with the ECM. It's definitely a work-around fix, but it was simple and has proved relaible.

I still think it's worthwhile to verify that the grounds in the tail section are good. If the ECM isn't grounded properly, it can cause really odd issues like this. Mr. Canoehead- your description of the operation of the sensor is obviously correct, however I think that a problem with the ECM grounding can result in it mis-reading the signal from the sensor. Excessive resistance in the ECM ground may mimic low resistance in the sensor.

If the bike is actually going into skip spark, it should display a check engine light (flashing IIRC) while it's happening.
Good point. I hadn't thought about ECU grounding affecting resistance measurement. However, that would cause all your sensors to read incorrectly (which may be the case here).

If the microamps required to operate the fan relay is too much for the ECM, the ECM is definitely on its way out. Or maybe the relay was bad in that case, causing it to draw too much current from the trigger circuit? I'm guessing in that example, the bike went crazy whenever the fan started up?

We haven't heard back from the OP but I would like to know why he thinks it is skip fire and not just a simple misfiring cylinder.

I still think that using an ECM reader to look at the live data would be the next step in the troubleshooting process. Blindly throwing parts at the problem is expensive.

Slightly off topic, I read an article a while ago about how BMW won't pay the car dealerships for replacing parts without justification just to prevent parts swapping as a diagnostic process.
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Old 08-21-2013, 05:12 PM   #18
gdsob OP
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Quote:
Originally Posted by Mr. Canoehead View Post
Good point. I hadn't thought about ECU grounding affecting resistance measurement. However, that would cause all your sensors to read incorrectly (which may be the case here).

If the microamps required to operate the fan relay is too much for the ECM, the ECM is definitely on its way out. Or maybe the relay was bad in that case, causing it to draw too much current from the trigger circuit? I'm guessing in that example, the bike went crazy whenever the fan started up?

We haven't heard back from the OP but I would like to know why he thinks it is skip fire and not just a simple misfiring cylinder.

I still think that using an ECM reader to look at the live data would be the next step in the troubleshooting process. Blindly throwing parts at the problem is expensive.

Slightly off topic, I read an article a while ago about how BMW won't pay the car dealerships for replacing parts without justification just to prevent parts swapping as a diagnostic process.
Guess it would help for me to subscribe to this thread..

I don't know if it really is skip spark, but it cuts out noticably after a while. The engine light sometimes comes on briefly then goes out.

I am going to borrow a Fluke meter from work and check the resistance of the sensors, then re-do the grounds as suggested. It does act like it could still be a temp sensor issue, but I'm just guessing at this point.
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Old 08-21-2013, 05:32 PM   #19
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Originally Posted by gdsob View Post
Guess it would help for me to subscribe to this thread..

I don't know if it really is skip spark, but it cuts out noticably after a while. The engine light sometimes comes on briefly then goes out.

I am going to borrow a Fluke meter from work and check the resistance of the sensors, then re-do the grounds as suggested. It does act like it could still be a temp sensor issue, but I'm just guessing at this point.

Does the engine actually stop running or does it just stumble?

My 06 had a lot of running issues, stalling, stumbling, surging and poor fuel economy. Turned out to be a bad TPS. Do you have ECMSpy and a cable?
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Old 08-21-2013, 05:45 PM   #20
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Quote:
Originally Posted by gdsob View Post
Guess it would help for me to subscribe to this thread..

I don't know if it really is skip spark, but it cuts out noticably after a while. The engine light sometimes comes on briefly then goes out.

I am going to borrow a Fluke meter from work and check the resistance of the sensors, then re-do the grounds as suggested. It does act like it could still be a temp sensor issue, but I'm just guessing at this point.
If it actually goes into the protective skip spark mode, the engine light will start to flash. From the owner's manual:

"If a fuel-injected engine exceeds normal operating temperature, the engine will operate in a "skip spark" mode until the temperature is back in the normal operating range. Reduced power will be experienced until operating temperature returns to the normal range. The check engine lamp will blink warning the rider of this condition. The check engine lamp will only blink as long as the operating temperature remains above normal. If the check engine lamp blinks excessively or potential overheating is not suspected, see a Buell dealer. "
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Old 08-21-2013, 08:28 PM   #21
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Originally Posted by Sharkguy View Post
If I remember correctly there is a member over on Badweb that cured his skip spark problem by manually wiring the fan to a switch on the bars. Supposedly the thinking is that the fan is powered through the ecm and the draw is too much for the ecm to handle on some bikes. Wiring it to the bars on a switch and bypassing the ecm takes a big electricial draw off of the ecm. I'm sure others can explain it better, but it can be found over at badweb.
My 2007 was also affected the same way. Etennuly found that putting in the manual switch to the fan stopped the skip-spark type running. I did the same mod to mine, and finally put an end to all the endless "try this" scenarios. Believe me, I tried all the suggestions at the time.
It was finally back to running great, right up until I found that I also had one of the 2007s with the bad cranks (43,000 miles - RIP).
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Old 08-22-2013, 05:15 PM   #22
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Fan ground

I don't know about earlier bikes, but my 08 XT fan gets it ground from pins 2 & 3 of the ECM J2 connector. I didn't like this current load going through the ECM so I added a relay that switches ground for the fan operation from a lug on the bike frame. The ECM just has to command the relay!

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Old 08-23-2013, 07:48 PM   #23
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Had codes 11 and 16. Sensors checked out ok. Re-did grounds. Not sure why the Tps code, didn't have one before, it might be from the reset I did.

Hopefully i have time for a test ride tomorrow, got three kids with opening day soccer. Freaking Cincinnati, opening day anything is cause for a parade.
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Old 08-28-2013, 04:55 PM   #24
Hughlysses
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Originally Posted by gdsob View Post
Had codes 11 and 16. Sensors checked out ok. Re-did grounds. Not sure why the Tps code, didn't have one before, it might be from the reset I did.

Hopefully i have time for a test ride tomorrow, got three kids with opening day soccer. Freaking Cincinnati, opening day anything is cause for a parade.
Any verdict on the attempted fix?
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Old 08-28-2013, 07:10 PM   #25
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Hugh, thanks for asking.

Haven't solved it yet. I got excited when i thought the temp sensor was open, but I was measuring the wrong pin on the connector. No obvious problems yet.

Was all set to order a diagnostic plug for the ECMspy, when my credit card got hacked. So there goes another week. Not too broken up about that since it's the hottest week of the year and I wouldn't be riding much anyway. Went dirt biking with my 9 yo last weekend and that helped scratch the itch.

I think once I can see the status of all the sensors and inputs, it should tell what is really happening. I also have a few 12v relays around to reduce the fan current from the ecm as suggested.
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