Thanks for the link. Looks like they anticipate you'll get 5 miles of weird behavior after every blend change so they want to minimize that. If you want to follow the instructions exactly you have to add in the "drive 5 miles immediately" part. Maybe he can just drive 4 miles since he'll be using E10, probably.

His 2003 isn't a flex-fuel vehicle though. It's just been using the "wrong" fuel for years.

"Switching Between E85 and Gasoline
We do not recommend repeatedly alternating between E85 and gasoline. If you switch from using E85 to gasoline, or from gasoline to E85, add as much fuel as possible, at least half a tank. Drive your vehicle immediately for a minimum of 5 mi (8 km) to allow it to adapt to the change in ethanol concentration. If you use E85 exclusively, we recommend that you fill the fuel tank with regular unleaded gasoline at each scheduled oil change."

 

Idle speed parameters are part of PCM memory, and idle speed will most likely change with E10 versus E85 due to different energy values for the fuels. It won't know anything it will just do what it does all the time based on what it measures, idle speed and O2 sensor values.

And, if nothing is changing then why the big deal. Nothing is different. We're kind of going in circles here. Like magic is going to happen.

 

Well, I guess I haven't learned *anything* having owned Ford vehicles for the last 29 years.

 

How about a description of what will happen if he just starts filling with 87 E10? That's what he really wants to know. I'd like to know too. Will something get damaged, will it run poorly? If there's a benefit to running the tank dry first, then there must be a detriment to not doing that.

Still very interesting that a person can apparently run E85 in a 2003 truck spec'ed to E15, with no apparent issues. Besides the conversation about how to get back to normal.

 

Clear codes or disconnect battery when refill.
It should resort to default and learn over again thru drive cycle.

These trucks arent even meant for e-10.

 

Not meant but still "allowed". If E85 didn't damage it, E10 isn't going to.

https://afdc.energy.gov/fuels/ethanol_e15.html

https://afdc.energy.gov/fuels/ethanol_fuel_basics.html