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Thread: Buell xb12scg after Dyno problems.

  1. #1
    Junior Member
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    Apr 2019
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    Buell xb12scg after Dyno problems.

    Hello. Im looking foor knowledge to help with my Buell. It is a xb12scg 2008 with a HP RS408 muffler and a K&N airfilter. A week ago it was on a Dyno adn it was set up as follows; TPS reset was done. After that the tuner added two dynojet lamdas into the headers. And after that the setting up began. We got a nice 92HP/107Nm.

    The problem is that yesterday as I started it after riding 15 minutes with it, it sounded like this when cold https://www.youtube.com/watch?v=xkh1Ttms7jU (not my video, but almost exactly the same symptoms). What might be the cause of this?

    Afterwards dynoing, I found this info;

    "On a Dyno

    Probably the best way to get the fuel maps right, as long as the dyno operator is good and knows a few basic facts about the Buell ECM.

    Always check or reset the TPS before setting up the Buell on a dyno. If this is not done and the TPS is out, then all maps setup on the dyno will be out by the same amount when the TPS is next reset. This can easily be done by the owner before going to the dyno shop. Don't waste your money asking the dyno operator to do this!

    Reset the AFV to 100. This is also essential and should be done immediately on arrival at the dyno shop. If the AFV is above 100 when you start tuning, it will be adding fuel above the closed loop area.

    Disconnect the O2 sensor! That's right, disconnect it before tuning on the dyno. If you leave it connected when setting up the ECM in the closed loop area, the ECM will adjust the AFV value and screw up the tuning! Remember to reconnect it when you have finished. The Buell ECM must be tuned for 14.7:1 Air/Fuel mixture in the closed loop area. Tuning for anything else will cause the ECM to set the AFV to correct it. End result will be incorrect maps outside of closed loop and potential risk of engine damage!

    If the dyno operator can measure front and rear cylinder mixtures independantly, then go for the best he can do. If not, make sure both cylinders get the same changes or you could run front spot on, and the rear lean!

    Always check the AFV value after tuning, it should be at 100 as the O2 sensor has been disconnected. Test ride the bike, ensuring you do some closed loop riding, then check the AFV again it should be between 90 and 110.

    CARE: It is known for a Buell to be setup perfectly on the dyno with the O2 sensor connected, but then to go off when used for a few hours. This is almost always because the O2 sensor was left connected, the bike goes through closed loop riding and adjusts the AFV. "

    Was the dynoing for nothing, now that we did not do exactly like this on the dyno shop..?

  2. #2
    Senior Member lowkey's Avatar
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    I don't have a ton of experience with the DDFI3 ECM but on a DDFI2 XB you can't simply unplug the 02 sensor to have it run in open loop. You need software and actually turn off the 02 sensor or clear the closed loop table values. Seems to me if you simply unplug the sensor the ECM would see 0 volts feedback and adjust fueling accordingly. On the 02 values within the ECM 0V is max lean and 1.2V is max rich. If you have access to software you can view the TPS value while it is running to rule out if this is your problem or not, or you could datalog and view all sensor feedback through MegalogViewer to chase down what the issue is.

    Again I've never run the bike with the sensor simply unplugged and feedback NOT turned off but I'd also guess you'd quickly get a check engine code for 02 always lean (IIRC code-13).

    AFV can be locked to 100% but this still will have no effect on the closed loop area of the fuel map, only open loop.

    This is the process for fueling inside the ECM:

    Base fuel cell value for TPS/RPM within the fuel map> + modifier (cold start, IAT, Temperature, OL 105%,WOT 110% etc...)>In CL ONLY 02 sensor feedback = GEGO % in real time at the cell value level>In OL ONLY GEGO % average across CL area = AFV% and applied to all OL cells with same %value.
    Last edited by lowkey; 06-01-2019 at 06:00 PM.

  3. #3
    Junior Member
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    Jun 2019
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    Aridrie AB Canada
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    Also make sure that you've disabled "open loop learn". If that is left enabled it will start adjusting your AFV value automatically based on riding conditions


    Last edited by Krypto; 06-21-2019 at 06:04 PM. Reason: spelling

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