With computer fuel injection a dirty air filter has no real effect on fuel mileage. The computer controls the mixture and compensates as needed.

 

In reply to post #16 about air filter effects.
The reply is not strictly true.
The Ox sensors will see a reduction is Oxygen in the exhaust and reduce fuel injected and engine power begins to drop.
The result is the driver applies more throttle which is more airflow through the engine up to the limit of the blocked filter.
The result of that is the Ox sensors detect more Ox in the exhaust gas.
The result of that is now more fuel injected that tends to lower the fuel mileage.
These are loop systems such that the last dominant loop determines the end result.
A blocked filter in FI has the same 'end result' it would have in a carbureted system.
Good luck.

 

jrossjr, if you used a half-tank of gas to drive to work and back, are you sure someone didn't siphon your tank?

 

I just purchased a 2010 f150 with 5.4 engine. In town and trips I only get around 14 mpg. Ant suggestions on improving the trip mpg