94 k2500 fuel mileage terrible

[hunter4ever12]

So I have an 94 k2500 HD extended cab, long bed, auto trans, with the 5.7L. I'm getting what I believe to be terrible mileage. I am only getting 12.5 mpg hwy and 10 mpg city. Granted I do have the stock steel rims so that doesn't help but I feel like I should still be getting higher mpg.

I have a few mods done to it as well, I gutted the silencer baffle for the intake, also removed the actuated gate for the pre heater hose and plugged off the opening in the air filter housing. I have done the ultimate TBI mod, quarter in the FPR (running about 17 psi now) installed the "salad bowl" and doubled gaskets under the injectors to make a homemade injector spacer. I also have a cherry bomb glass pack muffler. I'm not getting any codes, and the truck runs great has plenty of power. I do know I have 2 minor exhaust leaks at the donut gaskets that I plan on taking care of once the rain here stops.

But I can't figure out for the life of me why I'm still getting such horrible fuel mileage. In high school I drove around the exact same pickup only 2 wheel drive and was getting like 20 hwy and 16-17 city, so I feel like even though my current pickup is a 4wd I should still be getting 16ish hwy and 13 ish city or am I wrong? Any thoughts or ideas where I should begin?

[MikeCStig]

Check the ignition system starting with the easy stuff; plugs, wires, and distributor cap. Other than that, all I can say is that with what you have and what you've done to it, your fuel mileage is always kind of going to suck.

[777stickman]

What's the gear ratio compared to the high school truck? How accurate is the current speedo? Stock size tires?

[hunter4ever12]

Originally Posted by 777stickman

What's the gear ratio compared to the high school truck? How accurate is the current speedo? Stock size tires?

Shoot I didn't even think about the ratio... Not sure what it was in my old truck but my current truck has 4.10's...with stock tire size yes... Current speedo is spot on according to my GPS.

[777stickman]

4:10's in a 3/4 ton 4x4. I think you're MPG is just about what you should expect. (Love those GPS's for checking speedo.)

[Schurkey]

Originally Posted by hunter4ever12

So I have an 94 k2500 HD extended cab, long bed, auto trans, with the 5.7L. I'm getting what I believe to be terrible mileage. I am only getting 12.5 mpg hwy and 10 mpg city.

That's not far away from what my 5.7L, 1/2 ton, standard-cab long-box 4X4 is getting. And I have 3.42 gear ratio.

You're right in the ballpark.

[j cAT]

you have to fix the exhaust leaks. these cause the engine to run rich . 16mpg hyway is normal this old 15mpg is good. too much noise from the leaks will create also the timing to get kicked back KS reporting detonation because of the exhaust.

speed over 65MPH will cause rapid MPG drop .

[hunter4ever12]

I plan on fixing the leaks this evening so we will see what happens. Also as far as over 65 goes I rarely ever drive interstates here and literally all other highways have a speed of 65 or less so that's not an issue at all.