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Thread: Lean fouling the front plug xb12r?

  1. #1

    Lean fouling the front plug xb12r?

    It has a low idle and will stall after approx 20minutes of riding. When I first start out riding everything seems normal, and when Iím on the throttle it runs great, but after it hits operating temp, it wonít idle well. Iím running ngk 9s, an ebr ecm for the spec ops pipe I have. I have a breather-reroute and a k&n filter also.

    Iíve done TPS resets, Iíve cleaned, troubleshot every sensor on the throttle body, and checked for intake leaks. Everything is testing normal. My AFV is 100 for the front, 85 for the rear. I have an EGO of 78. Warm up enrichment of 103.

    The only consistent finding after 2 sets of fresh plugs is the front cylinder is fouling lean, the tip of the plug is white with ash. the rear plug looks great
    There are no CEL codes.

    Iím at a loss on this one. Any help would be great. I canít find any shop willing to help me with this bike. I have eeprom and maps from the bike

  2. #2
    Senior Member 34nineteen's Avatar
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    This happens a lot on 2005 models.

  3. #3
    Senior Member Cooter's Avatar
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    The greyed out front AFV of 100 means nothing. You don't even have a front O2 sensor. But both your AFV and EGO are leaning the bike WAAAY out almost to their limits. Why?

  4. #4
    Thatís where Iím confused. I think Iíve got the correct maps since itís the EBR ECM for the setup on the bike. I canít seem to find any mechanical issues causing it, but I havenít checked the fuel system. Could this be caused by failing injectors or something else?

  5. #5
    Senior Member Cooter's Avatar
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    1)A bad sensor or bad wiring can give bad info to the ECM causing this and many issues.
    2) ECM's RARELY go bad.

    IMO, check all the basics first and start at the beginning.
    Set your AFV and EGO both back to 100 and I bet the bike runs amazing. BUT I also bet it will adjust itself back to running lean again, soon. Avoid the temptation to lock the values at 100 because that would be masking an issue you have possibly causing more (and worse) problems.

    If you want to throw parts at it, a new O2 sensor isn't a bad guess and cheap enough.
    Hang the rear of the bike off the rafters or an A-frame ladder
    Remove the rear shock
    remove the fan
    Unplug the single wire to the sensor and use a O2 sensor socket or a 7/8" (22mm) crowsfoot wrench on a 6" extension to remove the sensor.
    anti-seize should be on the threads of the new one.
    Part# from the cross-reference thread:
    -GM OEM= 25162693
    -NTK= 21002
    -Airtex= 553071
    -Bosch= 12014
    -Denso= 234-1001
    -Walker= 250-21001
    -SNG= SN1-15

  6. #6
    awesome. I'll swap the o2 sensor this week and report back.

    I was able to find a complete throttle body assembly with new injectors, new sensors, and seals for a decent enough price. If the o2 sensor doesn't fix the issue, should I move to swap all of those things out at once with the new TB (since the price is cheaper than buying all those parts individually)?

  7. #7
    Senior Member Cooter's Avatar
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    Shotgun parts at it? Not my style, but you do you man.

  8. #8
    itís not ideal to shotgun parts, I get that, but without a shop thatíll touch it, and lacking the knowledge myself, I gotta try something. Iíd prefer to do things one at a time so Iím not wasting cash, but that complete throttle body really is a steal, and I couldnít find the individual parts cheaper. Iíf I donít need the parts now, itís nice to have the extras on hand.

    I swapped out the o2 sensor today, and reset the AFV like advised. It did run better, but itís doing the same thing as before, low idle and stalls when running at temp. The AFV held at 100 after a 30 minute ride, but my ego correction is now down into the 50-60s. Hereís the numbers I pulled today after the ride and o2 swap. WUE 103, IAT 102, AFV 100, EGO corr. 56.5. RPM is 800-900.

    I did notice for a short period my ego shot up into the 90s and the idle smoothed out, but it dropped back down shortly after and stayed in the 60s until it stalled.

    Now Iím left wondering Where should I check next? I ordered intake seals, and a crank sensor, weíll see what that does for it.

    Thanks for the help
    Last edited by patrickXB; 06-01-2021 at 07:11 PM.

  9. #9
    Senior Member outthere's Avatar
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    Check grounds also.

  10. #10
    Senior Member Cooter's Avatar
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    Ok so... what year bike are you riding?
    It depends on my TPS re-set instructions next.
    You can limit both the AFV and EGO correction limits to 90-110 and it should run OK as a band-aid for now.
    Checking intake seals is super easy, replacing them is a PITA but either way the ECM would compensate the other way with a high AFV, not a low one.
    "crank sensor"? Do you mean CPS? for ignition timing? If your bike is -08 and up only, and it wouldn't cause your issue.


    Last edited by Cooter; 06-02-2021 at 01:46 AM.

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