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Thread: Very noticeable flat-spot/sputtering in power-band between 4-4.5krpm

  1. #1
    Junior Member Polishblood's Avatar
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    Very noticeable flat-spot/sputtering in power-band between 4-4.5krpm

    Hello,

    When I bought my 2008 xb9sx (6+ months ago), I noticed a flat-spot in power-band around 4-4.5krpm. It's been getting worse and more noticeable ever since.

    It happens when I am using normal throttle operation, 50% roll on, to WOT operation, 100% roll on. (With the WOT roll on, the flat-spot can occur for a duration of up to 2 full seconds. Like literally my friends will be accelerating and my bike feels like it is just coasting with no power). As soon as the flat-spot/sputter is gone, by bike instantly kicks back into life with tons of torque. So top end power is very good. Literally the problem occurs only between 4-4.5krpm.

    (Under 3 conditions is the symptom less noticeable/avoidable) #1 To avoid the flat-spot or sputter, I have be VERY smooth on the throttle, roll on super slowly, and it won't happen. #2 If the fuel tank is topped off, especially with fresh gas, it is less noticeable. #3 When rolling on (normal to WOT) in first gear, sometimes the symptom is non-existent. The bike seems to power through it due to gearing.

    Bike has 12k miles. No check engine lights or codes (I think). Air-Filter was cleaned recently. Did a TPS reset, might do another. Spark plugs are new and gapped (I am using the colder ones). Stock exhaust. Everything is pretty much stock but air filter which is K&N.

    Do our xb9 bulls have two sets of injectors? Perhaps a second set of injectors that come on around 4-4.5krpm? Perhaps they are dirty? Bad fuel pressure? Although as I mentioned before, top end power is very good. So is low end power. Maybe bad AMPS to fuel pump?

    Would like to heard your thoughts. Thank you!
    Last edited by Polishblood; 06-21-2018 at 06:12 PM.

  2. #2
    Mine only has one set of injector (03), I would say check fuel pressure I think it should be around 50 psi, and have you checked your timing?

  3. #3
    Junior Member
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    You figure anything out with this one? I've been waiting for some of the gurus to chime in.

  4. #4
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    Had an 07 xb12Stt and I had something similar happen to me however my check engine would come on along with the issue. It would be right around 4000 - 4500 rpm's it would sputter and ride like hell, got worse and worse. I tried TPS reset and all of that but I eventually figured out that I needed to just clean off my ground cables as they were corroded from the salty air (So Cal by the beach). My battery was overdue for a change too but it literally was just the ground connection, so maybe check your ground wires that are mounted to the subframe.

  5. #5
    Junior Member
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    Have you checked "Noise reduction" on your ECM?
    Sounds like "White Wire Mod".
    In Ecmdroid: Ecm Parameters, General Config, Noise reduction.... Only Ramp Out enabled.

  6. #6
    Senior Member Cooter's Avatar
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    Do you have access and ability to use diagnostic tools like ECMDroid?

    You can check for historical codes, and go to "Live Data" and check the TPS, CPS.... and about a million other items to diagnose it.

    Otherwise we're guessing....

  7. #7
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    Guy's, your slipping, this is from JUNE !

  8. #8
    Senior Member Cooter's Avatar
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    I saw that NJ, just correcting some odd info



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