I have an '89 F250 with a 351 and a 4-barrel. Im getting about 6 MPG in city and 8 highway at 60mph. The only mods i really have is the 33" tires, but even with the stock 235/75/r16 tires the gas mileage was horrible.. i recently installed a new intake from K&N and have changed plugs, wires, dist. cap, went to a full synthetic oil and even had a fuel system plush done on the vehicle. The truck felt like it had run stronger, but the mileage stayed the same. Any thoughts on what could be the problem or any parts i can add to make this mileage better?

 

These trucks don't get good gas mileage. But I can say those big tires and the size of the gear ratio's front and rear has a lot to do with it.

First thing that hurts it is a F250 the second thing is the 4X4 and the third are your tires. Did you check your timing and see if the carb were set right?

 

I agree with SuperSnake, check the timing, the carb. float level and mixture screws. Also check that the exhaust is not restricted and that none of the brakes is dragging. Good luck with it.

 

Carb? is the power valve stuck open slightly?

Has the pollution control system been removed from this truck?

Is the inside of the tail pipe always dark soot black, spit black crap at anything sitting by it's tail pipe when it runs? Even before the mileage took a header?

If its not a hung up power valve and has always done it, it may need to be re jetted to lean it out a little, keep in mind to far is a bad thing. Not enough is bad to, running rich or to rich all the time leads to excessive ring to cylinder wear and will kill it almost as fast as being to lean.

 

This truck would have been EFI originally...
What gears does the truck have? It likely has a C6 tranny so hwy milage will always be single digits at anything over a double nickel. City milage will depend upon driving habits.

 

<i>This truck would have been EFI originally... </i>

Oh yea, seen the "carb" part and thought it was the same as my 87.

 

My 2wd on the smallest tires I could find and the EFI still in place only get 12-13 on the hwy with the lightest foot I can manage.

8mpg doesn't sound that far off for 4bl, 4wd, 33" tires.

Also make sure you are using both tanks when checking mileage. Gas has been known to miracle itself from one tank to the other on these trucks.

 

Did you adjust the odometer / speedometer to reflect the bigger tires? Bigger tires will make the mileage appear to drop if you don't adjust it.

Of course, I'm not sure how the speedo and odo get their readings on an '89...

 

Bear in mind that anything that creates friction will affect gas mileage, worn u-joints, wheel bearings, differential bearings, tire alignment etc. Alittle friction here and there and it begins to add up. Dan.

 

The truck is fuel injected and i changed the pollution control valve because it was horribly filthy and the hose clamp broke on one end. The timing was checked a few months ago and it was right on the money. As for the exhaust, there is a 2.5" glasspack exhaust accompanied by a 3" tailpipe.

 

He did say "4-barrel" in the first post.....

2nd on the PV, or perhaps the choke is hanging up.

What kind of K&N intake???
My stub stack was binding the choke rod until I took a Dremel to it.

8 is good for around town with my drivetrain.

 

the ujoints and bearings were all changed and everything with a grease fitting was filled with grease.

 

the only intake available from K&N for this year truck was the fuel injection performance kit.

 

So which is it? EFI vehicles (particularly these trucks) don't have a "4-barrel"...they don't have ANY "barrels", unless they are throttle body injected (which I don't believe trucks of this era ever were).

Jason

 

Sorry, I missed that, we posted at the same time......