Oh yes, I forgot one thing, Before you make the determination that your fuel mileage is poor, Get on the highway, Check the mile markers, and run for 10 miles, and compare to what your odometer says,,,, It could be well off, frustrating you,,, Mine reads slow in the cold weather, But not on warm days!
In the summer, I get 550 miles confirmed be a daily 100 mile ride on about 23 gallons of fuel!

 

One thing I saw mentioned that I would like to clarify is tire pressure. Inflate your tires for the proper wear. Don't over-inflate them to get better mileage. If 56 psi gets you the proper wear pattern and stability with the weight of your vehicle and load, don't put in 80 psi just because the tire says you can. Saving a few dollars here and there on fuel by having tons of pressure in your tires will not come near the price of replacing the tires prematurely.

 

One thing I havent seen addressed is injector condition. Get them checked, as one time, I got them cleaned and reset, and gained 4.5-5 MPG!!! That is right, I went from 15mpg city to almost 20mpg city. Had 4.10s, so hwy MPG was about the same.

Also, since you have an auto, get a tach on there, and see how many revs you are turning at highway speeds. Mom's has a super sloppy aftermarket, stock spec torque convertor, and it turns about the same revs at 70 as it does at 60. I did a stall test, and quit at 2000rpm. It wasnt even trying to lug the engine down. Stock is 1750; ideal is around 16-1700, depending on mods and usage.

Daniel

 

I have two 93 D350 Club Cabs, one with the 5 speed and one auto. the 5 speed has been averaging 20mpg mixed city/highway driving and about 17-18 pulling the 11K trailer.

The auto is getting about 15mpg doing the same driving, I havent hooked the trailer to it yet...

Just sold the 5 speed , so I gotta do soemthign to get the auto running better, sound like its revving high for the speed I am going.. no tach yet to tell tho

 

If it sounds like it's revving too high, it probably is in the torque convertor.

DP

 

Yeah, thats what I am afraid of...$$CHACHING$$$.....
Its got a heavy haze at start-up and idle, so I am also thinking dirty injectors.. gonna check on having them cleaned and pop-tested as soon as I get the $$ from the grey ghost..

 

Mine hazes at start up and idle and the injectors are brand new with a fresh maxed pump rebuild. It smokes darker when I nail it, but clears right up when the turbo spools up. I can't complain except the obvious, need more turbo.

 

I just bought the truck three weeks ago today and it has a brand new( two days before I got it) reman IP from a shop in Hutchinson KS.
I am realy hoping to avoid having to pay to have the tranny pulled and a TC put in right now... i can live with poor mileage for while as long as it will pull the trailer..
clutch is going on the tractor, and I cant afford both..