[Norm Peterson]

It's a durability thing. Running slightly leaner can make a little more power as well, but exhaust gas temperatures tend to climb, which brings onthe potential for damaging the converter(s) and possibly other components, particularly in sustained higher rpm / higher load running. So Ford errs on the rich side in order to reduce warranty expense (and I'm sure that they have people running the money numbers between measured fuel economy/CAFE vs anticipated warranty). Probably why the FRPP power upgrade packages need to be dealer-installed in order to get any warranty on them at all.


Norm