I verify the ethanol content via my fuel trim. If I put in appox E30 and put the setting jn for E30 and the fuel trim stays at 0-3%, then I know I'm at E30. If I do the samething and the fuel trim says "+7% " I simply adjust the stoich setting more towards the Ethanol being greater. If I set it to the E30 setting and the STFT says "-6%", then I change the Stoich more towards the higher gas content and i know I'm not at E30.
I error on the side of more ethanol than gasoline. I can simply stop at any fuel station and add .5-2gal if the ethanol content is too high. If the gas content is too high, I have to tap into my extra 5gal tank that I keep at home, but I never run "too much gasoline".
Its a little bit of math. But at least its fairly easy. I generally work off of 4gal of E85 to a full tank of 93oct.
With the map switching in access tuner, its epicly easy after you do it once or twice.
If I'm running a new mix ( more or less than 4gal Eth per tank ), I'll give it my best guess at map #3. Then if I guessed high, I simply switch to map #2. If that still isn't enough, i switch to map #1.
Once I get the stoich setting, I lock it in across all 5 map slots reflash and carry on like nothing is new ( assuming the tune permits the same timing/boost ).
My way is almost $300 cheaper and just as accurate, if not more so since your actually seeing what the car is currently doing on the fuel in your tank. That being said, if you knew basically what the real content was right off the hit, then you could avoid this simple, but sometimes cumbersome step.
If you never change your mix... Like generally never leave my 4gal per tank of eth vs the rest being 93oct then its gonna be about the same.
The system can swing 30% in ethanol direction or 30% in the gasoline direction in real time. So 5-7% isn't going to sink the boat, the idea is just to be as accurate as you can for the ECU, so that it doesn't have to put forth as much effort to change the fueling for you based on other calculations and inputs, which by nature have a bit of built in flaw-ing ( but are pretty dang awesome still ).
Also when you guys are pumping E85 at the station, keep in mind your fuel system holds a good bit of fuel. Its not like the second you start the engine its going to be running a perfect mix of the fuel in the tank. It may take a second for the high Eth fuel to reach the cylinders, and it may even take a bit for the mixture to reach its end E30-type number.
IE: you may start your engine on 93 oct, then it will suck almost pure E85 from the bottom of your tank, the finally the fuel will mix and you'll start to get the correct mix for that tank. It happens fairly quick, just be aware. I baby the car for the first mile or two ( after I idle the car for a couple seconds and see the STFT going "holy crap". Then I drive real soft for about 1-2 miles. Then I watch the stft at idle to see where I'm at.
In text, it prob sounds like a lot. It maybe for the first time. Just remember how easy sex is now, and how complicated it seemed when you were 15... By the 3rd tank of E30, you'll be an expert
