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Thread: 2003 XB9R running TERRIBLE please help!

  1. #1
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    2003 XB9R running TERRIBLE please help!

    2003 xb9r 30k miles. Bought it as a project. Will start and idle for a short time before stalking out. You can rev it and keep it running but it runs like absolute crap spitting popping backfiring etc. I replaced the fuel pump assembly from the get go knowing it would be needed at some point anyways. 50psi with switch on and will hold right at 49-50 while running. TPS has been reset countless times, a known good ECU has been tested with, relays and fuses all checked. OEM plugs, wires and reluctantly a coil have been replaced after I tested my original coil with my DMM on the wrong setting. After getting desperate I noticed that unplugging the engine temp sensor allowed the engine to continue idling great and made the bike rideable but not great. As any normal person would do I ordered a new temp sensor and after weeks of waiting for it I got it in annnnd it ran like it crap again. I checked ignition timing and found the cam sensor to be what I thought was burnt. I replaced it and timed the bike but it made zero difference in runability. The bike doesn’t throw any codes unless I unplug a sensor while it’s running. When I original got the bike AFV’s were 108 so nothing abnormal there. The intake seals aren’t leaking. What should I look at next? Any ideas at all? I’m desperate at this point and just about ready to boot the project and cut my losses.

    Edit this is my 7th XB. I was on bad web for ages but lost my log in and it appears there’s no mods approving memberships anymore there so I can’t sign back up. I’ve scoured the Facebook groups with zero luck.
    Last edited by Sagostino; 01-18-2023 at 09:26 PM.

  2. #2
    Senior Member Cooter's Avatar
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    Have you actually set the idle?

    Did you perform the procedure exactly like the service manual states too? It will run exactly how you describe if done incorrectly, no matter how many times you do it.

    http://buellmods.com/content/downloa...olt_manual.pdf

    Section 1.16 for Idle, section 1.19 for TPS

  3. #3
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    Yeah, unfortunately I’ve reset it 20+ times. I’ve even intentionally set it WAY out of spec just to see what type of reaction it causes and honestly it doesn’t change a whole lot…..one detail I forgot to mention is that if I set the AFV to 150% the bike will start and idle correctly all day long. I’m aware that the AFV that high is compensating for some other type of issue, just not sure what that issue could be.

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    Quote Originally Posted by Sagostino View Post
    .one detail I forgot to mention is that if I set the AFV to 150% the bike will start and idle correctly all day long.
    So, you're saying if you trick the ECM into thinking its running really lean, it will run correctly? So, it sounds like the bike is dumping a lot of fuel into the engine and if setting the ECM to trick the injection into going super lean resolves it, you probably have something like an injector stuck open. I would pull the injectors and run the injector test on ECM Spy or Droid and look for the difference. Either way, I would send them to our friend Chaz Aagaard for cleaning and flow testing.


    Have you checked the O2 sensor? This is kind of a really long shot, but the Bosch ones are only $20-ish.

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    High AFV equates to more fuel so it’s actually like the bike is running lean without turning AFV’s abnormally high. I have pulled the injectors and tested the spray pattern. I did not check the flow rate on them though. I have also spoken with Chaz several times. He’s a wealth of knowledge and very helpful. We were convinced it was fuel pressure issue but I have 100% eliminated that.

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    You are right, I had them mixed up.

  7. #7
    Senior Member Barrett's Avatar
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    You are increasing the "pulse width" of the fuel injectors by 50% every time you dead-lock the AFV to value 150. That is masking a serious issue elsewhere.

    If you are receiving an occasional active CEL blip with no stored historicals it is almost always FC's #13 & 16.
    A failing( I did NOT say faulty) 2003-only side stand switch can adversely effect idling by intermittently cutting off ignition.
    Cracked/leaking TB intake assembly
    Failing O2 sensor without stored historical
    Missing or improperly installed airbox baseplate-to-TB connector boot
    Perform both static room temp WOT compression check both cylinders and leak-down test
    Two of your symptoms point towards an unhealthy engine from both abuse and excess heat cycling

    Good luck.

  8. #8
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    Hey thanks for the reply! No check engine light activation at all after start up. Can you explain a little more about 2 of the 4 symptoms. Which two symptoms are pointing to an unhealthy motor and what’s indicating abuse and excessive heat? Any ideas on why the bike runs much better with AFV’s set to 100 and the temp sensor unplugged?

  9. #9
    Senior Member Barrett's Avatar
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    Yes Sir my pleasure. First edition XB9 Lightnings and Firebolts are the 68 Road Runners of the motorcycle world. One of the most disgustingly abused motorcycles in modern history. Tradition..."project bike"...20 years old....air-cooled...all combined to point towards a motor that's internally unhealthy. Additionally, you have no baseline from which to move forward with your diagnostics and trouble-shooting.
    An accurate compression test @ WOT for both cylinders along with a simple cylinder leak-down test will reveal the engine's health. You'll have no idea what you're truly working with here until you perform these tests. Plus the peace-of-mind they provide is priceless.

  10. #10
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    and with that said, school is out.

    Principal Barrett Strickland will be keeping an eye on you slackers.




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