The case for an ethanol sensor.

Since I found that a dirty mass air flow sensor dramatically reduces MPG. I haven't driven far enough since the "fix" to have tank to tank data but the trip fuel economy has jumped at least 10 MPG. So I've been thinking how the MAF can have such a dramatic effect when the ICE is generally operated "closed loop" with the fuel flow rate adjusted to achieve complete combustion a determined by the sensors in the exaust. My conclusion is that other "tuning" of such things as valve timing, spark advance, exhaust gas recirculation is done primarily on the MAF data. So the dirty MAF "detunes" every thing but the fuel air ratio. Then I observe that EPA testing that gives us their fuel economy rating is done with E0 fuel. Very few of us have access to E0, we are forced to burn what we can get which has been E10 and soon will be E15. All that tuning is off because we are using a different fuel, even the air fuel ratio should different, 14.7-1 for E0, 14.08-1 for E10. In theory E10 should result in about a 3% hit over E0 if the engine is tuned perfectly in each case. But I and several others have observed the hit is between 5% and 10%, I think I understand why now. Hopefully Toyota will add an ethanol sensor, they are on every "flex fuel" vehicle, and multiple tuning maps to the prius family soon so we get close to advertised economy on available fuel.