Flex fuel kits relatability

[Zelek]

Last time I checked, Lund only does wideband flex fuel tunes. Unless something changes, they don't do in-line fuel sensors like other non wideband cars.

Flex is a transition tune not meant to run full time but you can if you want.

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[Plimmer]

The coyote engine operates in closed loop mode all the time, meaning the ecu gets constant feedback from the wideband sensors. It targets a lambda value commanded by your tune. If you’re using e85 or eWhatever the ecu will adjust the fueling to the lambda commanded in the tune. If you have an nguage or similar you will see that it targets lambda 1.0 at cruise and idle and around 0.82 to 0.85 at wot. There is no delay it does this instantly. The adjustment the ecu does shows up as a Long Term Fuel Trim and Short Term Fuel Trim (LTFT and STFT). You can see this on your nguage as well, and you’ll see the STFT changes instantly and all the time as the ecu fines tunes fueling.

Timing is also adjusted by the ecu based on a calculated flex fuel content (if using a flex tune) and feedback from the knock sensors.

Bottom line, if your tuner has setup your tune correctly, I’d be surprised if a piggy back system can do a better job than the stock ecu. I would also love to see a dyno test showing that e85 makes more power than e80 or e75, or even e70.