If the ecm doesn't actually know what fuel mixture your engine is running at, then it cannot adjust the Inj. Pulse width to compensate for altitude, weather, ect... So.... Why have Sensors at all.... Do away with Map, Coolant temp, Man. Temp, throttle Position, ect... the reason it was done away with on the Saudi exports, along with the Cat, was Leaded fuel, and they had to program around it on the chip... these trucks had to be tuned just about every 10k miles..., like in the old days on Pre 74 model/points triggered cars... Damn, Just about told my age... :grin: