I just picked up an original F150 4x4 with a 4.9L with 30,000Miles on it and it is in great shape
I replaced the plugs, wires, rotor, cap, air filter and used some pretty strong cleaner in the throttle body and let it soak over night, and yes a lot of black came out the pipe
I have the stock size tires that I am running 35psi in them, and I put a cap on it
I took some wd-40 and sprayed it around the motor to see if I had any vacuum leaks
I don't drive around with hugs locked at all
WHen I first got it I was getting about 370KM per tank, now I am getting 300K or less which is about 10miles per gallon
I have checked and I don't have cross filling in the tanks
I do mostly highway driving and I drive like and old lady because of the bad mileage


I do not drive it hard at all and slow down in advance for lights things like that

Am I missing something here? I am stumped

any suggestions would be appreciated

Gunnar

 

Hence the reason they stopped making them.

The few friends I know that have I6s, 10-12 mpg seems to be the standard

 

The decrease could be winter blend gas. You also may need a new front O2 sensor.