So when most people run an alternate fuel such as q16 they simply program a different MAP and then switch between them when they change fuels. This works because Q16 = Q16. The problem with E85 is that there can be a very significant variance between gas stations….geographical locations, time of year..etc etc. So, If you tune your car on E85 that happens to have X% ethanol and then 2 months later fill up with E85 that has 85% of X ethanol content your ECU is still referencing the static map that it was tuned on. This could cause your car to run poorly…or become to lean during a 30PSI pull. Either way, its no bueno. So the solution that Haltech uses is a GM modified flex fuel sensor that detects the Ethanol content in the return fuel line. Not what it is supposed to be….but what it actually is. So plumbing would be as follows: Fuel pump -> Filter -> Fuel Rail -> FPR-> Haltech Flex Fuel Sensor->Return line to tank To tune with E85 a 93 (or 91) octane tune is done first to establish a baseline. Then a tune is done with only E85 in the tank. But instead of building a separate map everything is done on a gradient table which changes based on the percentage ethanol present in the fuel. So at the point you have a 93 table and data from E85. From there they start doing blends…50/50, 70,30 etc etc. To make sure that what is expected to happens from an A/F and timing standpoint actually happens. So if with 93 octane you can safely run 20 psi And with E85 you can run 30psi If it’s a half / half blend boost would in theory automatically be set to 25 psi (just a guess but it should be close) Ignition timing and A/F are done the same way and then checked at different mid way points. This works because Haltech is tuned off of volumetric efficiency. So once it knows exactly how your engine moves air it can make any other adjustments. What I like about this is if your out and can’t find E85 but you still have ¼ tank you can still fill up with 93 and not have to worry about it. The other cool feature is that with their wideband system you can plug in X% trim and based on temp, humidity, altitude etc etc it will adjust your tune in real time to make sure everything is where it needs to be. If you have anymore questions let me know and Ill do my best to help. Here are a couple of pics of the setup on my Supra. 


Madhatter10-6
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