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Hey y’all I have a 97 mustang GT with a vortec with 80# ford injectors and bigger fuel pump keeping rail pressure at 40 psi bigger throttle body stock headers with free flowing exhaust. I’m having some issues tunning the car on E85 the car runs great on 91 but as soon as I change the stoich AFR to 9.733 for E85 of course with tested E85 fuel it runs like shit I have to pull the maf curve back and then it throws off my load tables but the car runs good. But then my MAF#min are a lot less do I have to rescale somewhere else ? Any insight would help !!
 

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If you want to run a flex-fuel car, your ECU needs to have flex-fuel capability and you need to have a sensor in your fuel line that minimally reports the % ethanol in the fuel. Ideally, you want % ethanol and fuel temperature. To run an E85 fuel with a variable ethanol content your ECU needs two fueling tables. One table is for gasoline and one table is for ethanol. Depending on the data feed from the flex-fuel sensor the ECU will interpolate between the 100% gas table and the 100% ethanol table to arrive at the proper fueling. The OEM ECU can not do this.

That doesn't mean you can't run E85, however it does mean that the pump variety of E85 which can vary from 51% to 83% ethanol is going to give you a tuning headache without a flex-fuel capable ECU. The correct solution for this is to get the proper GM flex fuel sensor, plumb it into your fuel system and then get a flex-fuel capable ECU. The easiest and IMO best flex-fuel capable ECU choice, is the MS3Pro Plug and Play unit that plugs directly into your existing wiring harness, runs your dash like an OEM ECU, and provides all manner of tuning tools, capabilities, and failsafes that are not available in the OEM ECU.

Do a search on the site here and read up on the MS3Pro PnP. It is the short way home, for you. While you are at it, look up flex fuel sensors on the site and read up on them also.
 
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