Lean when going from E85 to 93 oct

[maxgee]

I've been on E85 for 3 yrs. Recently I took a trip on the Hot Rod Power Tour and had to use 93 octane. I was on CL SD and thought putting 93 the computer would adjust and I would be fine. Well as soon as I filled up with 93 the car would go lean under load. I had my labtop and put it in OL, adjusted the VE so I could continue on my trip. Ran 93 the rest of the trip; on a good note I got 33mpg! Car has been sitting since 2nd week of June. Wondering what could be the hiccup with CL SD on 93 octane?

[flame]

The stoich point of E85 is 9.7 where gasoline is 14.7. You are looking at a 50% difference there. The fuel trims can only compensate for 25%. If you want to be able to switch between the 2 you need to tune it with both and reflash when you have to run 93.