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I've been having misfire issues with my UTV 400 when it gets warm and I've thrown all kinds of parts at it so far with no permanent resolution.  Today I removed the O2 sensor and it is black on the end.  To me that means it's running rich and/or the sensor isn't working.  I replaced the sensor with a new one and will see how it goes I guess.  With EFI, I'm wondering why the sensor would be this way with low hours and mileage?  Is there a way to adjust or lean out fueling on these?  Thanks in advance.  

I was randomly and briefly able to connect to my Coleman UTV 400s ECU the other day twice and haven't been able to since.  When I was able to access it, I found the following codes and wondered if anyone may know where I should start or what I should look at?   P0031 - O2 Sensor Heater Control Voltage Low P0107 - Manifold Absolute Pressure/Barometer Pressure Voltage Low P0113 - Intake Air Temperature Sensor Voltage High P0118 - Engine Coolant Temperature Sensor Voltage High P0650 - Malfunction Indicator Lamp (MIL) failure  

Just picked up a Cub Cadet 500 that had shift issues (corroded fan gear) which I fixed. It also didn't seem to be running smoothly then all of a sudden it got worse. It seems to miss on both idle and when pushing the gas pedal to the floor and doesn't seem to be running at full power. I've been working with a local person who is walking me through some steps, but I'd like some input from this group as well. What I've done: - drained the fuel tank and replaced it with 93 octane fuel and added heet to help with any water problems. - replaced the fuel injector. - disconnected the battery (several times) to allow the module to reset. - set the valve clearance, both intake and exhaust, within specs ... intake was tight but exhaust seemed fine. - replaced the battery. - replaced the O2 sensor. Nothing has helped. Not sure what the next steps are, but would appreciate any expertise that can be offered here.  

Just picked up a Hisun 500 that had shift issues (corroded fan gear) which I fixed. It also didn't seem to be running smoothly then all of a sudden it got worse. It seems to miss on both idle and when pushing the gas pedal to the floor and doesn't seem to be running at full power. I've been working with a local person who is walking me through some steps, but I'd like some input from this group as well. What I've done: - drained the fuel tank and replaced it with 93 octane fuel and added heet to help with any water problems. - replaced the fuel injector. - disconnected the battery (several times) to allow the module to reset. - set the valve clearance, both intake and exhaust, within specs ... intake was tight but exhaust seemed fine. - replaced the battery. - replaced the O2 sensor. Nothing has helped. Not sure what the next steps are, but would appreciate any expertise that can be offered here.