1998 expedition, 5.4. i just got the superchips programmer and used it and can already tell a difference even though i only have it on the 87 octane setting. my question is this, i live in south dakota and in order to get gas in a higher octane rating i have to get it with ethanol added into it. so does one keep it on 87 octane and regular gas or will it hurt or maybe help if i set it on the tow setting and used 89 or 91 octane that has 10% ethanol?

 

You really need to ask Superchips. They may have any updated tune that accounts for ethanol (which, BTW, typically has a higher octane rating).

 

You go by the octane rating of the fuel, forget about if it is E10 fuel or not. I'd bet money the 87 octane you run has ethanol in it.