Turns out it's because there's more oxygen in ethanol fuel! I know someone here touched on oxygenation of fuel but I didn't look into what they really meant.
"Another effect of the oxygen from ethanol is that
ethanol blends tend to run "leaner" than pure gasoline because there is more oxygen available in the fuel-air mixture.
My car wouldn't change the airflow through the AFM because without the 02 sensor in the system, it has no idea it's getting more oxygen from the ethanol fuel. Since I'm not talking big swings in the AFR, I was never concerned. I just always wondered why I saw that difference when going from pure gas to ethanol.
Quote:
Originally Posted by chapo
My F150 that was Flex Fuel would go from 17 MPG to 13 on Ethanol. Not cheaper in the long run at all
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That's huge! My F250 only drops about 2 mpg but it's a pig. I'd feel happy if it ever got 17 mpg.