Fuel guzzling troubles
 

Hello, I am new to the Ford idiot lifestyle and thought I would try it so I went out and bought myself a 1986 ford F350 work Truck with a 6.9 mated to a t19 tranny. I have heard people rave about fuel economy on these trucks, saying that they get anywhere from 20-30,and I thought OK, that's great, a diesel that I use for work with great fuel economy, awesome, then I got the first gas bill. 10 mpg, are you serious?! So I swapped all eight injectors because I noticed an unnatural amount of smoke coming out my tailpipe, swapped those and it eliminated 80% of the smoke, however when I replaced the injectors, one of them scared me that my engine might just be cooked from the previous owner, it changed from the regular grey to dark brown on almost the whole body of the injector, and just the one. I put the engine back together and then do another fuel economy run, and guess what, 10.5 mpg still!! I always weigh 9k and I am very light on the throttle, any suggestions?

Oops didn't mean idiot I meant IDI, stupid auto correct

What gears do you have and how fast do you drive?

Being a work truck, do you have any extra weight added, like a flat bed, utility bed, etc.. If you are smoking a lot, the PO may have turned up the fuel screw in the injection pump. My 93 with 4:10's and a 5spd got 18mpg when I first got it, but after my grill guard, tool box, bigger tires and all the other junk I bolted on, I was usually around 14.5mpg, closer to 12 on the freeway. I did have an 86 F-250 with 3:55 gears and the t19 that would get 20mpg all day long, but it was a bone stock standard cab long box truck.