Been running E85 in my 02 5.4L for quite a while. Decided to switch back to gasoline. The 25 gal tank had 8 gals left in it so I was gonna switch tunes back to gas and fill up. I switched to the gas tune and ran the truck on the remaining E85 to the gas station. I filled up with premium and drove back home. It ran good and since I still had 27.2% alcohol I kept an eye on the fuel trims. Runs a little rich but not bad.

 

I've heard that a STOCK non-flex engine without a tune can handle up to about 35% alcohol without throwing a lean CEL