How lean is too lean for a modern (non-lean burn) car and how rich is too rich? Reason I'm asking is my new 4 cylinder Mazda 3 is going through catalytic converters like shit through goose. The dealer has been unable to solve this problem. Looking at the fuel mixture and its ECU, Its WOT fuel mixture is set at mid 11.5:1 air fuel ratio and part throttle is stoich 14.5:1. I want to do my best to keep the cat safe and prevent meltdowns. Do you think it's set to run too rich? Would 12.5:1 be a safer ratio given I retard spark to prevent knock? thanks...
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