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Thread: So what's the problem!?!

  1. #1
    Senior Member lowkey's Avatar
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    So what's the problem!?!




    I could write a novel, but I'll try and keep it short and sweet. I went for a ride last week about 50 miles to start dataloging to tune my maps, also worked on dialing in a square idle for two days before that. It was either later the same day or the next day that when I started the bike, it wouldn't idle for more than 20-30 seconds and backfiring through the intake. I flashed the saved EEPROM I had on the bike since I bought it but no change. Keep in mind the ride I did with the modded map was fine, just back to the stock one to rule it out.

    Here is the video description to quickly cover what I've already done/looked over.

    No codes(ECMSpy), TPS reset, purged fuel, changed plugs, tested coil/wires(OK), checked all harness wiring/ecu for cracks, wiggle tested(OK),static timing checked(OK), inspected cps(visibly looks OK)

    In the video I hold the throttle steady trying to keep 3,000RPM's the fluctuations are the bike not throttle input to be clear. This is also the longest it has kept running at idle all week, and engine was cold for video. Note you can see EGO's going wild to keep it idling.

    So I'm open to ideas here, I feel like it is going to end up being the cam position sensor but I really can't drop $130.00 without knowing for sure. From the threads I could find SOME people describe similar symptoms and no codes, except it gets worse as it gets hot(on theirs). Other posts say it threw all kinds of codes or won't run at all.

    To test it proper I'd need an oscilloscope, which I don't have.http://www.badweatherbikers.com/cgib...89#POST2241189

    Or there was this tread stating he saw abnormal voltage for CPS in TunerPro but never followed up if the bike was fixed. He also posted screen shots of doing it with TunerPro but I'm not a member so can't see em...
    http://www.buelletinboard.com/forums...with-CEL/page1

    Is that lag on the diagnostic page with the CPS box (0 green 5 red)? Its either signal lag/drop out from the CPS or bluetooth to ECMSpy refresh lag but I'm not sure which...

  2. #2
    Senior Member Cooter's Avatar
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    It's gonna be hard to start diagnosis in the middle of where you are now and not know the basics.


    Backfiring through the intake can be a sign of bad or erratic timing, a bad CPS can do that, and so can a lot of other things.

    Being lean can do that too. Checking Fuel pressure should be easier.

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    Senior Member AZmidget91's Avatar
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    Always check the mechanical stuff first. Fuel pressure and intake seals.

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    Senior Member lowkey's Avatar
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    Quote Originally Posted by Cooter View Post
    It's gonna be hard to start diagnosis in the middle of where you are now and not know the basics.


    Backfiring through the intake can be a sign of bad or erratic timing, a bad CPS can do that, and so can a lot of other things.

    Being lean can do that too. Checking Fuel pressure should be easier.
    Basics of what?
    Quote Originally Posted by AZmidget91 View Post
    Always check the mechanical stuff first. Fuel pressure and intake seals.
    Forgot to mention I checked seals and that they've been replaced not to long ago with James blue seals

    As for fuel pressure, if pump primes and shuts off as normal is it not triggered by proper pressure? Seems it would keep pumping to build pressure. The last ride mentioned had no issue with power/lean condition... then all of a sudden...

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    Senior Member AZmidget91's Avatar
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    The pump needs to provide constant pressure while flowing. If it isn't flowing it is easy to build the pressure even with a problem.

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    Senior Member lowkey's Avatar
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    Quote Originally Posted by AZmidget91 View Post
    The pump needs to provide constant pressure while flowing. If it isn't flowing it is easy to build the pressure even with a problem.
    Should I see constant 51PSI even when running? No pressure drop for open injectors? I can borrow one and try tomorrow.

    Cole, what about the CPS box lag in the video on ECMSpy? Normal to read like that?
    Last edited by lowkey; 03-13-2017 at 04:20 AM.

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    Senior Member Simplymichaeljr's Avatar
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    In the video it looks like the drop in rpm is happening at the same time as the lag in timing. Did you check the timing by putting the bike on a stand and putting it in fifth gear and checking it using ecmspy?

  8. #8
    Senior Member Chicknstripn's Avatar
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    I believe he stated that he did perform a static timing test.
    Normally in a situation like this I would say to check the intake seals. Even if they have been replaced recently the repair could have been done halfhazardly. I'd perform a test to make sure the intake seals are sound. Google "Buellxb intake seal test" and you should get some good direction on that.
    The other thing I would check is the fuel pump. However, you have mentioned that it primes normally.
    How old is your O2 sensor? Your issue could be the O2 not reading correctly.
    What does your AFV read before and after a ride?

    There's a way to test the CPS using a heat gun or hair dryer. I wish I could lead you to the post where someone used this procedure but it been a while.
    I think the gist if the test is you heat the CPS with the hair dryer and the bike starts to act more and more erratic as the heat builds up. I've never tried this test but see if you can find info on it.
    The above test might not help you if your O2 is bad and hasn't been ruled out. Faulty O2s exhibit symptoms as heat builds up.

    Not sure if I've helped or just confused you more.

    Good luck

  9. #9
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    There's a way to test the CPS using a heat gun or hair dryer. I wish I could lead you to the post where someone used this procedure but it been a while.
    I think the gist if the test is you heat the CPS with the hair dryer and the bike starts to act more and more erratic as the heat builds up.


    that's precisely correct carlos. a heat-gun works well...a hair dryer won't do the job. run the bike till you can feel warmth however slight in the cam cover particularly around the bullet area. then with bike idling heat the bullet area which holds the cps assembly. use common sense but if the cps is faulty and in particular those with "goop" leaking out of the assembly....the addition of heat will cause erratic behavior and even shut-down.

  10. #10
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    I will say that I had this problem with my 09' XB12 back when i first got it... It turned out to be a TPS sensor on its way out... never threw a code. It would backfire out the intake and sputter and die unless I rolled on the throttle.



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