My 99 F250 7.3 PS, 3.73 gears with 97,000 miles on it is getting now getting 15.4 mpg. When I bought it and after the break in period I use to average 17.3. Then all of a sudden it dropped down to the 15. That was after my fuel sending unit went out and I had Ford put in a new one. My last trip from AL to CA on one tank full it averaged 17.0. Go figure. I still run it at 75 on Cruise control. I thought I saw a post that said something about the filler tube on the 99 model had some type of problem of allowing more air in to the system. Anyone have any ideas? What is a good chip for the truck.

1999 Ford Lariat SD 7.3
1962 & 63 Ford Econoline P/U

 

I have a f-350 dually crew cab with the 7.3.Wether (i know my spelling sucks lol) im in the city or on the highway,loaded or unload my milage stays the same (15 mpg) even with the 6637 mod didnt help any.Im in constuction so i let the truck idle alot.But this does not seem to affect it to much in anyway.But i have heard that alot of people are getting 13 to 21,but never happened with me.This is my 2nd truck and they were both the same way.Even my buddys truck gets the same as mine,same truck just 1 year older then mine.

 

The Magic number is somewhere around 70mph, right around 2000rpms -- That's the sweet spot on the 6.0L's

 

I run my 99 F250 C/C at 70 mph / 2000 rpm and it still gets 15.6 down from 17.3 that I use to get a couple of years ago with it.

 

Just by chance, is that because the max torque for the 6.0 is rated at 2000 rpms?