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They decouple estimation of air mass from sensors for redundancy, modularity and diagnostics. Air mass can also be estimated from air pressure sensors and throttle angle or valvetronic lift along with temperatures and other values/calcs.
Fuel mass has a pilot calculation based on desired lambda and estimated air mass. Closed loop feedback from lambda sensor optionally comes later.
It is so much more complex than an ECU of 20 years ago where you could write the entire equation for injector pulse back to the MAF sensor on the back of a small envelope. Slightly simplified leaving out closed loop lambda: IPW = lookup(injdeadtime) + constant * lookup(MAFvolts) / RPM / lambdatarget.
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