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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 Peeking Turtle's Avatar
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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
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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

  9. #9
    Junior Member Polishblood's Avatar
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    Hello friends. Two years later and I am still dealing with the same issue. Now that the coronavirus is giving me more time at home, I want to fix this issue immediately.

    I need your diagnostic help. Everything that I said in the original post applies. To clarify, it is not a complete loss of power or even a sputtering issue, rather its a large hesitation in power which is happening at EXACTLY 4,500rpms. The bike runs AMAZING at every other rpm.

    My thoughts are that it maybe an oxygen sensor, IAT, fuel injector, or fuel pressure related issue. What are your thoughts? Could these items be the issue? How do I go about diagnosing these items? I am unfamiliar with the diagnostic software out there so please leave a link if you mention one.

    Let's get this done guys. I am looking forward to everyone's expertise.

    Cooter, you mentioned ECMDroid, I will look into it tonight.
    Triumph, ground cables are good and attached well.
    Malaguita, never heard of the "white wire Mod". What is it? I will try to check it out tonight.
    Last edited by Polishblood; 04-07-2020 at 08:11 PM.

  10. #10
    Senior Member 34nineteen's Avatar
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    Your first step would be to get a service manual. Being that you asked if the motorcycle has 2 sets of injectors per cylinder tells a lot.

    And yes, it does sound like the 2nd set isn't kicking in and the sensor probably needs to be recalibrated using dedicated service equipment. There are actually 4 sets of injectors per cylinder. The first set does idle to 1500 rpm, the second covers 1500-3000, the third covers 3000-4500 and the 4th set covers 4500-redline. On the 1125's all the injectors kick on at once, which is why they make so much more power than an XB.


    For someone who wants to fix an issue "immediately", you're are going to wait until "tonight" to look into diagnostic tools? Is Bridgewater in Hawaii?


    Start your diagnosis here... www.buelltooth.com. Tell him Cooter sent you, not me...



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