What big block engines were available in the 1990 f-250 ext. cab xlt. and what rpm should the engine be running at 55 mph? My father in law just bought one to pull his camper with and while the truck has plenty of power the gas mileage is not so great,( below 10 mpg) weather he is pulling or not thanks for any help.

 

460 and the rpm`s depend on rears tires and transmissions.

 

the 90 F250 engine options were the 4.9 liter 300 inline 6 cylinder, the 5.0 liter(302), the 5.8 liter(351W), the 7.3 diesel, and the 7.5liter(460)
look at the 8th character in the vin. this will identify the engine size.

Y= 4.9 300cid
N= 5.0 302
H=5.8 351W
G= 7.5 460
M=7.3 diesel