So if I data log for an email tune using E85, will the tuner be able to tune for 91/93oct? Obvious answer would seem that I would need to be running the fuel type to tune for, but maybe I'm wrong?

For a flexfuel capable truck.

 

Only tune for what fuel is being used. There is nothing wrong with switching fuels if you are tuned for it, but you can't accurately tune for pump gas when you are running E85. My truck for example advances spark when you are using E85. If you would like to swap back and forth, start with pump gas, then switch over to E85 after your tuner has successfully tuned for pump gas. Let you tuner know what you are doing though. They might even tell you that they will only stay with one fuel because it can be a pain.

 

Makes sense. I think that has been a problem, that my tuner hasn't been clear that I'm running E85 when he tunes for me. So you think it's better to tune on gas before E85?

 

Yes because when the E85 threshold is met, it will add timing based off of your base spark tables. If your base spark tables are not correct from proper tuning, you are adding degrees of timing to something that is not accurate. That is just one example.

 

That makes sense. Thanks!