misfire, sputter @ lower RPM only at max engine temps

[xb9r]

Hello again, Eddy here.

I had a chance to put some miles on Dads Firebolt and I will say Buell’s a little unrefined for me but so is Dad. He left me a bunch of parts, the service manual, and ONE inherent issue. He said I could figure it out and I’ve been after it all day.

The issue;
The Buell runs absolutely perfectly for a couple miles until you can feel the heat crawling up your leg (wow) then it sputters between 2500 & 3k RPM in any gear for the rest of the ride or until you shut down and cool off.

Misfire was my interpretation so I have eliminated the following from this chapter to include changing fuel, COMPRESSION tests, new plugs, cleaning all the grounding points (per this forum’s suggestion) I learned how to use ECMSPY and reset my throttle position sensor a couple times to be sure and test rides produced the same scenario.

He had a second (extra) race ECM tuned for Jardine so I swapped that and it ran the exact same scenario, smooth operation for a few miles then misfire between 2500 & 3000 RPM.

The only obvious thing I found was one spark plug wire. Dad said he was aware and had already bought a set so I installed the new ones BUT that didn’t solve the misfire within the lower RPM today. Um... I think I like this hunt, are these not the simplest and easy motors next to Harley's, wait it is a Harley nm.

Because it runs GREAT for a couple miles all potential fuel issues are eliminated in my mind. I ordered a new coil for the heck of it but I can probably test the current one. I have a feeling the coil is fine.

Here is my question to the board;
Given what little is left on this checklist and the nature of perfect engine performance (until warmed up) what else of the remaining 8 can I eliminate off this list (automatically) so I can focus on where this problem might be?

Sorry don’t want it to be the last item LOL that’s just no way to start a new relationship with a Buell. Any help might shorten my effort and YES these are interesting motorcycles!

 

[Chicknstripn]

Running issues that occur once bike builds up heat can be:
O2 sensor
Head temp sensor
CPS(cam position sensor)

Chances are it's the O2. Do you know if the O2 has ever been replaced? They're not too expensive and a quick search should net a Bosch part number that can be found at your local auto parts store.

Does the cooling fan operate normally? If so I'd assume the temp sensor is ok.

To test your CPS ypu can visually inspect it; if the sensor on the back of the timing plate is goey it's probably bad.
You can also test it by allowing the bike to fully cool. Then heat the CPS with a hair dryer till its hot to the touch. Fire bike up, if it exhibits the hot running problems you described with engine cold and CPS hot you know you need to replace it.

BTW I can not take credit for the CPS hair dryer test. Another member came up with it and I wish I could remember who it was so I give due credit.

 

[TPEHAK]

Clean and tighten battery terminals.

 

[Cooter]

Do all that stuff ^^^^^
and it still might point to a lean issue as it only sputters after the cold-enrichment stops.

A simple way to cheat that is to use the ECMSpy you have, and up the AFV to 115 or so. That will globally enriched the entire map. If that helps, you can then go down the tuning wormhole...

 

[xb9r]

Running issues that occur once bike builds up heat can be:
O2 sensor
Head temp sensor
CPS(cam position sensor)
I will get on these right away and get back to you thanks!

Do you know if the O2 has ever been replaced? It has not

Does the cooling fan operate normally? Yes

thank you

 

[xb9r]

A simple way to cheat that is to use the ECMSpy you have, and up the AFV to 115 or so. That will globally enriched the entire map. If that helps, you can then go down the tuning wormhole...

This was too tempting and the result was a sputtering cold and hot engine so I was encouraged because I'm not ready for Buell "tuning wormholes" LOL, I set it back to 100%.

However ECMSPY threw a solid fault after THAT jerky ride ---> 'TPS short to ground' BOOM BABY! I went straight to this wire leading to the TPS sensor that apparently has been scratching on the frame. I don't know if this short is the fix for the whole sputtering but I thank you Cooter for the rough ride as I previously had no errors past or present to know what was happening. You literally had me shake this short out tonight. Congratulations my Dad will be proud.

Chicken's new O2 sensor will be in tomorrow so depending on how the bike runs after I fix the short and how much trouble it is to change an O2 sensor I might do that too. Hey can we let pops think I know something for a couple days at least, then I'll tell him I had good help :up:

 

[Chicknstripn]

There is a method of replacing the O2 sensor that requires rear wheel removal, disconnecting of shock from frame(not swing arm) and removal of cooling fan. This gives direct access to the O2 sensor.
I've used this method myself and it's much easier(and faster) than rotating the engine.
Google "buell XB O2 removal" and you should stumble upon a very informative thread.
Two other tips when performing remove and replace: 1) spray old O2 with liquids wrench or something similar to assist in freeing it from the place it's called home for the last 14yesrs. 2) put a little anti-seize on the threads of the new one so your kid doesn't have the same issues
Good luck

 

[xb9r]

There is a method of replacing the O2 sensor that requires rear wheel removal, disconnecting of shock from frame(not swing arm) and removal of cooling fan. This gives direct access to the O2 sensor.
I've used this method myself and it's much easier(and faster) than rotating the engine.
Google "buell XB O2 removal" and you should stumble upon a very informative thread.
Two other tips when performing remove and replace: 1) spray old O2 with liquids wrench or something similar to assist in freeing it from the place it's called home for the last 14yesrs. 2) put a little anti-seize on the threads of the new one so your kid doesn't have the same issues
Good luck

I'm feeling pretty good about this short being the end of the story tomorrow when I get back out. All buttoned up and fingers crossed I won't forget what you are saying about how to install the 02 sensor if needed. I saw engine rotation in the SM and WHAT! Nice to know there is a short cut. Good luck means the sensor goes in the future parts bin tomorrow and not on the bike

 

[TPEHAK]

If you have chain conversion there is no need to remove rear wheel, just rear shock absorber and fan, it takes 10 minutes to replace the oxygen sensor.

 

[xb9r]

Thanks for the tips and tricks :up: Closing this issue with the chaffed TP sensor wire shown above as being the cause of, and solution for my sputter and missing at certain RPM's that induced enough vibration to short it out against the frame/fuel tank.

Repair was made and the slight repositioning of the TPS jack connector more up and over that tight area. BIKE RUNS PERFECTLY but does not explain why it ran fine until warmed up since this was a short to ground issue. I got nothing on that but maybe one of you can explain.

Now that I had an opportunity to familiarize with the Buell and use diagnostic software I realize the 02 sensor will show an error code if and when I need one. That sensor from my local auto parts store looks like a perfect match for the Buell (good to know) but I took the 40 dollar refund and went for a exhilarating ride instead.

Moved up one rung on Dad's approval ladder today. He says I'm barely good enough to keep his Buell and that I will appreciate the heater as the weather turns LOL.

Eddy rides Buell now................. END!

 

[Cooter]

Glad you got it sorted, and Thanks for posting the solution:up:
Honestly, I'd put in the O2 because you have it. They don't usually just fail, they get lazy slowly.

Enjoy the ride! "You have a headlight out!" haha