I have a 3.0V6 Flex Fuel truck and I put E85 in it for the first time since I have owned it and after a while the CEL came on and its lean codes for both banks. Any ideas what could be causing this?
On the other note the truck is running smoother then it ever has, idle, excel, everything is running much smoother.

 

Welcome to the forum

What year Ranger?
earlier FlexFuel used a sensor on the fuel line, and these did fail, $650 price tag

Lean on both banks means computer is having to open the fuel injectors longer than it calculated for the air flow.
Computer does on the fly calculations based on RPMs and air flow, and opens the fuel injectors for a few milliseconds, based on fuel pressure, to inject the correct amount of fuel.
If computers calculations are off by more than 15-20% then it will set Lean code
It adds the extra fuel, so engine should run OK, the code is set to notify driver of the calculation problem
Gas only will have set "open times", Flex Fuel needs flexible open times

Ethanol is a 'weaker' fuel than gasoline so more is needed in each cylinder, which is what the sensor told the computer, "add more fuel as more ethanol is detected".
In later models they just allowed the computer to add more fuel with out setting lean codes.
Flex Fuel engines needed bigger injectors, and different computer software, thats the only real difference between gas only and FF

Switch back to gas only and see if the Lean codes go away

And post year of the Ranger

 

I Cleared the codes and they didnt come back. maybe it was just adjusting.
Its a 2000