| I am trying to understand how the ECU calculates A/F alphas. I did a lot of searching on this. I might be wrong about a lot of what I think I know, but here are my questions. I understand that the O2 sensors indicate to the ECU if the AFR is rich or lean as a deviation from a stoichiometric mixture. If I understand A/F alphas, they exist to nudge the mixture richer or leaner by a constant percentage across the closed loop region in the fuel maps. The idea being that the TPs in the fuel map aren't always going to be 100% accurate (with a basis on a stoichiometric mixture) due to slight variations in the performance of various sensors and parts. Since almost none of the fuel map actually calls for a stoichiometric mixture, the existence of A/F alphas seems to indicate that the ECU is capable of determining if a fuel map enrichment/enleanment value actually produced the desired mixture as a deviation from a stoichiometric one. In other words, if a fuel map cell actually called for a 14.7:1 AFR, then we could just nudge fuel one way or the other in some programatic way until the O2 sensor voltage was one that we know always indicates a stoichiometric mixture. But I think only a small number of fuel map cells, at least on my aftermarket ECU, actually call for a mixture near 14.7:1, exactly. Assuming that's not all totally wrong, my question is: how does the ECU determine the AFR for a given O2 sensor voltage reading, which I think it'd need to know in order to work backwards to determine if its TP is actually generating a stoichiometric mixture? Is it just a simple calculation within the narrowband the stock O2 sensor works in, based on the assumption that some value (~450mV I think?) indicates a stoichiometric mixture? Thanks.
Andy
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