To run true flex fuel where the ECU makes changes on the fly to different ethanol %, you also need a ethanol sensor setup.

DrivenFab makes one. Flexconverter makes one (I use that one). They are both Plug and Play.

Then you will need the Tephra XMOD V3 rom for your ECU to actually enable flex fuel tuning: http://www.tephra.it/v3/

 

A little OT but related question I have for those out there that do tune actual flex fuel. When your doing that are you cutting the E-85 with 87 octane? From what I remember Ethanol is mixed with low octane gas to formulate E-85 so thats what would make sense to me. I have no real world experience trying to do this though so I'd be interested to hear about how its done in practice.

 

No, I use the highest grade available. So 91 or 93.

 

Is that a little CYA for the tuning process?

 

No. It's because a Flex Fuel tune is creating a tune that runs from pump gas up to 85% ethanol, so I tune between pump gas that is put in the car (Premium) and the highest ethanol percentage put in the car (approx E80-E82)

For example, here in California it's going to be between 91 octane (E10) and E85 (approx E80).

 

That makes a lot of sense. That scenario probably happens pretty often for people going back and forth. Thanks for explaining.