A "Lean O2 Sensor" Code does not necessarily mean that the mixture is actually "Lean".. Remember that the name of the sensor is the "Oxygen Sensor" NOT the Mixture Sensor. Therefore; anything that might cause a lot of Oxygen in the exhaust will generate the conditions that are required for the ECU (Computer) to set a "Lean O2 Sensor" code.

So, what might these be?
1.) The Mixture really might be lean. A bad or plugged Fuel Injector for that cylinder would be the most probably cause if the mixture really is Lean. If it were anything else the problem would either be occuring with both cylinders or your idle speed would be really high.
2.) Any sort of a misfire will increase the amount of Oxygen in the exhaust. The misfire can be caused by either a fuel or an ignition problem; it doesn't matter. Remember that the Oxygen Sensor is only measuring Oxygen; so even though a misfire may be dumping a lot of raw fuel into the exhaust the Oxygen Sensor doesn't measure fuel. A misfire will not use any fuel and it will not use any Oxygen either. So a misfire (no matter what the reason) will look like a Lean Mixture to the Oxygen Sensor because the Oxygen content of the exhaust will ALWAYS increase when there is a misfire!
3.) An exhaust leak between the Cylinder Head and where the Oxygen Sensor is located in the Exhaust Pipe. The leak doesn't have to be very big to cause a lot of headaches. You may not even hear it! While it is true that there is a high pressure shock wave that travels down the exhaust pipe every time the Exhaust Valve opens . . . what is also true is that between each of these High Pressure Shock waves is a Low Pressure wave. This is part of the principle that a Header Exhaust System uses to increase the performance of an engine. Anyhow, when the Low Pressure Wave passes a leak it will draw outside air into the exhaust pipe and the Oxygen Sensor will interpret this as a lean mixture.
4.) An Oxygen Sensor that is failing may not be able to generate it's normal voltage range of 0.0 to 1.0 Volts (Typically 0.450 Volts = 14.65/1) where 0.0 Volts is Lean (lots of Oxygen in the exhaust) and 1.0 Volts is Rich (very little Oxygen in the exhaust).

I think you said that you swapped the front and rear Oxygen Sensors and the problem stayed with the cylinder. This should tell you that the problem is definitely NOT the Oxygen Sensor.

 

thanks for all that...no i did not swap the sensors, replaced exhaust and used new gaskets and properly seated them...with the old headers the o2 sensor situation happened in the rear pipe, with the new headers it happened in the front one, in both cases only one is going crazy ...this is why i don't think the sensors are bad....this would also eliminate the posibility of a blocked fuel injector?...how can i notice a misfire?...the idle is between 976 and lows 1000, without any noticeable changes...
i'll take off the exhaust and put it back together, a time consuming job with a 2 into 1 that has the headers welded together

 

wow while all that may apply to the stock o2 sensors it would not to the wide band. the code for the engine was not lean, it was P0131 Front Oxygen Sensor Low. meaning it is not getting the data pulse it is looking for. I could move the wire around and the code would go away. i replaced the sensor and it was fine. best source of info is to report to TM and they will respond with the info.
http://www.thunder-max.com/Support/F...onSupport.aspx

 

said i would remove the exhaust and put it back...didn't, instead got drunk and watched fifa game...this morning i cleared the code and went for a short ride...everything went fine, no code, no check engine light...so maybe a false alarm?...whatever happened before didn't today, which was the first time out after the mods....thanks all

 

mine still comes and goes when i move the wire so i am sure it is bad

 

does your engine light come on?...any dtc?...which are the symptons?

 

yes all the above
po131

 

excuse my ignorance, could this be related to heat?...have you cleared the code thru the speedo and then ride?...including highway so the engine cools off

 

yes cleared the code but it will return and heat does not have effect on it.
it will go away if i move the o2 sensor wire

 

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vapor from the anti seize some times will mess up Ur sensors...