I had these symptoms.
https://www.ft86club.com/forums/show...&postcount=243
My cause was the flex fuel kit's feed pressure sensor was reading low, which triggers a "safety" feature of the kit to zero out the E%. The cause of the low feed pressure was the in-tank fuel sender pump not being fully seated. If your kit has Bluetooth and the pressure sensor, try downloading the DT app and reading the feed pressure.