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Thread: XB9 sudden misfire.

  1. #1

    XB9 sudden misfire.

    Hello.

    I got a strange phenomenon today when driving my XB9S on the highway, i had been driving for about 80mph in 20 minutes when the engine suddenly misfired when i gave full throttle and the engine-light flickered. I did press in the clutch and the engine reved nice. And when driving off the highway was everything ok. I know the plug wires rubber caps are cracked, can it be the reason? But i did only happen on the highway.

    I did check the system with ECMspy and did notice the AFV value had went from 115 to 135. The misfire did happen a few km from home so it might have gone high and not got back to normal value.

    There was no fault codes.

    Any ideas? Can it be the very hot weather we have today that affect? About 30 degrees C.

  2. #2
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    Well, first idea would be to replace your plug wires and then see if it happens again.

  3. #3
    Quote Originally Posted by njloco View Post
    Well, first idea would be to replace your plug wires and then see if it happens again.
    Hi, it seems it was so called ”skip spark”. Probably in combination of very hot weather and speed around 130-140 km/h, but i will for sure change the plug wires any way. Thx for support.

  4. #4
    Senior Member Cooter's Avatar
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    Probably not "skip spark".
    And an AFV of 135 is telling you it has a problem. Most likely an intake leak.

  5. #5
    Quote Originally Posted by Cooter View Post
    Probably not "skip spark".
    And an AFV of 135 is telling you it has a problem. Most likely an intake leak.
    It had 135 10 min after it happened, it went down till 116 again. Intake seals are new, but it did happen again a few days ago. When giving full throttle does it misfire but when open it slowly is it ok. This only happen on the highway in 5 gear when accelrating from like 140 km/h, not during normal accelration. Strange.

  6. #6
    Senior Member Cooter's Avatar
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    That high load, high RPM situation taxes the fuel pump to max demand, and will show a weak one or compromised fuel line in the tank (pinholes).

    An AFV of 135 is showing the ECM is trying to richen the global fuel map quite a bit, also possibly from a weak fuel pump?

    You should test it.

  7. #7
    Quote Originally Posted by Cooter View Post
    That high load, high RPM situation taxes the fuel pump to max demand, and will show a weak one or compromised fuel line in the tank (pinholes).

    An AFV of 135 is showing the ECM is trying to richen the global fuel map quite a bit, also possibly from a weak fuel pump?

    You should test it.
    Sounds like a good theory, is it enough to check the fuel pressure or do i need to remove the pump?

  8. #8
    Quote Originally Posted by Barrett View Post
    it's starved for fuel. you mentioned in 1 of your threads that you "rebuilt" the pump.
    you mentioned in the thread below that the pump is "new".
    which is it?
    if new, it's a faulty installation or faulty pump.
    if you rebuilt it, something incorrectly done during that process.

    https://www.buellxb.com/forum/showth...358#post623358
    Pump is new. But i will have to remove it and check. I did not change the hoses inside based on they looked like new, but they might be bad. Is it ordinary fuel hose used inside the tank? To be honest do i not think the stock pump was bad, maybe better to put it back again.

  9. #9
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    Quote Originally Posted by Fredrikrosen View Post
    Pump is new. But i will have to remove it and check. I did not change the hoses inside based on they looked like new, but they might be bad. Is it ordinary fuel hose used inside the tank? To be honest do i not think the stock pump was bad, maybe better to put it back again.
    It is ordinary FUEL INJECTION fuel line. High pressure. Make sure you get HIGH PRESSURE fuel line.

  10. #10
    Today did i put back the stock Walbro pump, a new hose between the regulator and the metal filter and a new regulator from Quantum. It primes nice, have a good flow when putting the fuel line in a bottle. The fuel pressure was 50psi when the pump primes. Now just waiting for my new ht leads before i will take if for a test ride.



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