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Author Topic: Misfires, Flat spots and O2 sensors  (Read 373 times)


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Misfires, Flat spots and O2 sensors
« on: October 09, 2018, 08:16:15 AM »

First post here but the forum has helped me out a lot.

I have a 2012 GT250 (Naked) EFI. Its a great starter bike and I love it but it has had an misfire since I started riding it right around the 5.5-6.6k rpm mark.

Fixes I tried were:
-New plugs - nothing
-New caps, leads and coils - nothing
-New ECU - nothing
-New O2 sensors - nothing

There is no dealer where I live and only one bike shop that will work on hyos and they couldn't figure it out.

I have managed to fix the issue by simply unplugging the O2 sensors.

I theorise that given the bike had high flow air filter and exhaust on it when I bought it, that it caused the AF ratio to be different to what the ECU expects/requires when it reaches the emissions testing rev range @ around 5500 rpm, so it responds by leaning the AF ratio but due to the higher airflow it's too lean and it misfires.   

I don't know if that's right but it's fixed so I'm happy.

However, what remains is the annoying FI light on the dash. I have tried resistors to eliminate the sensor/heater but none of them keep the light off.

Does anyone know of a sensor eliminator that works? I have seen the magnum tuning one but they run $100USD a piece and I would need 2 of them (I think) so I'm not leaping at that.

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