Asking a cat to tackle 2300ppm is asking alot. I don't think I'd look at the cat. Using a lower grade fuel than the car calls for can increase nox, but again not that much. The 3rd cause you posted may be the key. The engine may not be geting rid of the heat.I am still waiting for the chance to prove this myself, but several months back a guy posted that his 107 SL was running 1200ppm. He replaced the radiator for different reason and nox went to way below passing.


Peter

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