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Cats are lit by temperature of exhaust gas flow. Oxygen sensors (newer versions) are electrically heated to get them to operating temperature, which is something like 800 degrees. Frequent on off cycles allow the cat to cool below the point of proper function.
If I read correctly the XB passed emissions, on the second test, but did not function in the ideal range of what is normally expected. The second oxygen sensor in the exhaust system is there to monitor the function of the cat and the first sensor.
I Don't think Sentra had any codes except for the misfire codes he posted, which means the system should be functioning within acceptable parameters, but the range of acceptable parameters could be far higher than the ideal, which he made clear he was not happy with readings that did not closely match "ideal".
I'm not posting here to question his judgement in that area. Apparently he has a high threshold of personal responsibility when it comes to pollution, which I find to be an admirable sense of personal responsibility.
It may be that to find a balance between his extraordinary efforts at efficiency he has gone outside of the parameters of the design of emission controls that the factory provides.
The question is where is the balance of emissions and efficiency that satisfies him and only him.
It could be as simple as coasting with the engine idling, but that would affect his mileage significantly. I have tried the techniques of engine off and for the amount of work involved to me it was excessive and had some negative consequences as far as longevity of components.
Not a criticism of any one's efforts at conservation just my personal experience. It's also the reason why when I am travelling alone I usually ride my 2011 CBR, weather permitting, which has a cat, fuel injection and a feedback system like late model cars. I can get 72-85 MPG while employing mild techniques and enjoy the ride at the same time.
Again, Sentra, I hope you can find an acceptable solution. I spent some time thinking about your situation, and try to provide some suggestions based on my knowledge and experience. It does not mean I am right and everyone else is wrong, just some thoughts about possible solutions. They could be right or wrong, I hope they help.
reagrds
Mech
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