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Discussion Starter #1
Hello all, I am scratching my head and hoping to save some hair.
I have 2002 Xterra with the the 2.4L 4. I have been tracing a rich burn condition that baffles me. When the outside temperature is above 40 F my gas mileage drops by 3-4 mpg and after a while I get a code indicating the catalytic converter. Below 40 F my mileage goes back up and after a while the code clears. I have tested the MAF and the IAT sensors and both are functioning within spec. I am suspecting that possibly they are not operating in a linear fashion and the ECU is getting bad input at only higher temps
Does anyone have resistance specs to check calibration of the sensors? Any other thoughts or directions would also be appreciated.
 

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Discussion Starter #2
Further thing that I should make evident. The change point is fuzzy not hard like my first post seems to say. It consistently is in the rich condition before the temp is 50 degrees ambient. It is consistently running good by about 33-35 degrees. The mid point seems to be at 40.
 

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Great question. Yes, both of then have been replaced. It is also confusing that the MPG drops along with the change in the light. If I stay Highway only the difference is a little over 2 mpg
 

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Discussion Starter #5
One further item as I continue to chase this. I reviewed history in the ECU and found a code for random misfire that occasionally accompanies this issue. I am having thoughts that a failing crank position sensor is starting the loop issue. Then the ECU is compensating for the misfire and resulting in the slightly rich condition which is active.
Any thoughts from the gang?
 
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