Hello folks!

I have own a 1994 Ford F-150 XLT Single Cab, Long Bed, 4.9L Straight Six - 300, 4 speed E40D. I currently get around 10mpg city and 13mpg Highway. I've seen that this truck is rated for at least 15, not granted this isn't new, I assume this is a bit below where I should be. Currently has about 219,021 miles. I tuned it up, replacing all of the filters, spark plugs, spark plug wires, the center tank has a brand new bosch fuel pump. I have 31" A/T's. Any ideas of where to start?

Thanks for your time,
TheKhaos

 

Another thing, I mainly run 92 to 93 octane fuel.

 

what gears are in the axle(s)? Ford put 3.08's in some of these trucks,god only knows why,and 31's and 3.08's will cause poor mpg's for sure.

 

Your bigger than stock tires are sucking up fuel. What gears do you have? Check for stored codes first and foremost. Your truck will know what's going on. If you are running higher than 87 octane, you are wasting money. Your truck isn't making enough compression to NEED that, nor is it self adjusting to the different fuel.

 

Haha, for whatever reason I feel the truck deserves the best, that's why I get 93 octane, pretty stupid. Not sure how to check for what gears I have. I have noticed the Check Engine light flickers on when I turn the key to the ON position. Haven't had a chance to pull the codes.

 

This.

The axle code is on the door jamb sticker on the drivers door...Right below the door striker on the cab.

It'll have a 2 digit code such as "17" or "H7"...Get that and report back.

 

Alright, Thank you sir. AXLE - 18

 

That's a 3.08 open diff. That's your problem (maybe among other things)

 

Well, looks like I may have to just deal then. I really don't want to go back to the stock tires. I'm not sure what gears to get if I did decide to change them, or where to even start. Any recommendations?

 

3.55 is the lowest gear ratio ford offered in the F150. If you wanted to switch to that, you could find a whole rear axle in a junk yard and just swap the rear axle instead of having to tear a diff apart. You can usually get a whole axle for a couple hundred bucks. Whereas gears alone may cost you more than that. If you do a lot of city driving, you may want to swap in 3.73 gears. Ford didn't offer that, so you'd have to order them.
If you have a 4x4, you have to do both front and rear axles by the way.

 

It's 2WD, that is definitely something to consider. I really appreciate the detailed information. Thank you for your time.

 

No problem bud.

 

really i have 31s 3.08s and an e40d and i get 22 mpg regularly what speed do you drive?

 

I wouldn't condemn your gearing and tires so quickly as your main issue. Sure it doesn't help, but it shouldn't effect the mileage that much. I have 33's, stock gearing and a 5.8 with a lift and I can get better mileage than that. There is something else at fault here. Check for codes to see if anything comes up. Even if the light isn't on, there can still be stored codes.

 

I'm not gonna call you out on that; But I'm not exactly buying the farm either...

My truck hit 20.92 mpg ONCE in the 2 years I've had her.

Probably one of the most "In-Depth" tuned up engines around, including a small timing bump..

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As for the gearing....3.08's are fine, if you're not in a hurry, and want some semblance on mpg.

3.55's, (What I'm swapping to) will put you back to the power rating of the I6/3.08's are factory

As for the tires...Anything larger than 235/75/35 sized tires (Stock for F-150), is gonna cut mpg....The tall/wider the tire, the more it'll cut.

And you're truck will absolutely struggle to get the tires rolling.

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I say toss some stock sized tires on, and see where your mpg stands.

Taller tires will also make your odometer mileage un-accurate...So your mpg readings aren't gonna be correct.

If you see how many % the 31's are larger than the stock tires, and add said % into the mileage, it should give you a true-er mpg reading.