1999 K2500 continuously gets 5mpg

[Jeepwalker]

Did you say what your rear end gearing was? Also, is your tk lifted with large tires? If you have the wrong gearing (tires and gears), electric fan on all the time ...those things could make a difference. Is it going into closed-loop mode? Is the temp sensor reading correctly? (sorry if you mentioned those already). I would think the worst it should get is 8-9mpg.

Try this TCC test: On your TCC, take a drive down the highway, flat road, steady cruising at, say, 55 mph and just 'tap' the brake pedal while steady cruising. The TCC should disengage, and you'd see (& hear) a slight rpm increase. It's almost like shifting out of a gear but not as dramatic.

 

[L31MaxExpress]

Yes rich. What you've stated is also my understanding about the ECU's ability, and why the tuner said it isn't really anything to worry about. He's convinced that the ECU (black box) is getting bunk information form something but I have literally swapped every sensor on the engine to no avail. At this point the only things I can think of is either a ground somewhere that is funky or driveline drag.

Yes, you are right - EGR would not drop milage by this much.

My L31 got better mileage without EGR and the 383 gets nearly the same mileage as the 350 did.

I would be checking the truck after a trip around to make sure that brakes are not dragging. A hanging caliper will make the truck feel down on power and heavily increase fuel use. The wheel would be scorching hot on a dragging caliper situation.

 

[Keeper]

Any noticeable fuel smell from cab/bed gap? Those fuel tanks have a plastic shroud that holds debris/salt between it and the tank. A small hole will leak at the evaporative rate so no fuel ever hits the ground, but you should smell it. The lower on the tank that the hole is, the worse the mpg.

 

[Philip Parker]

Tire size, lift?

stock.

 

[Philip Parker]

Any noticeable fuel smell from cab/bed gap? Those fuel tanks have a plastic shroud that holds debris/salt between it and the tank. A small hole will leak at the evaporative rate so no fuel ever hits the ground, but you should smell it. The lower on the tank that the hole is, the worse the mpg.

There is a faint smell of fuel actually. I will check it out, thank you.