Your engine's ECU operates in open loop control before the engine is up to operating temp., under WOT, and under heavy load conditions.
Otherwise, while cruising or at idle, it operates in closed loop, and references O2S input signal to continuously balance fuel injection, in order to maintain a stoich AFR. That is what fuel trims indicate - the minute, incremental adjustments to fueling, in order to achieve stoichiometry.
And the stoich AFR between ETOH laden gas and conventional (or E10) is different.
Your E30, oxygen enriched gasoline is starving the engine for fuel, which is why you see fuel trims max out in the positives, and why your mileage Sucks, and the ECU is dumping tons of fuel into the cylinders.
But, under WOT, when you're having the most fun, the E30 (or whatever) will lose its effect pretty quickly, because the stock ECU tables are not formatted to truly utilize the benefits of ethanol blends - your utilizing E10 open loop tables formulated by Ford engineers with your E-whatever. Your AFR and timing tables will act accordingly.
Though, I do figure, like I've already stated, there is a possibility the ECU references a separate set of tables, if certain conditions are right, onset by E15 or E20 use. These cars, afterall, are "E15 ready", correct?
Even so, I dont doubt the benefits at all of E. In fact, I threw a couple gallons in with my super the other day. Seems to work nicely with my stage 4 Livernois tune. I haven't logged any date yet, however.
Check out black death or fuel pump black gunk on Google. Some people go too far with E.
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