I cannot believe I just read 30 posts of this...

A single-tank MPG reading is completely and utterly useless. I miss Gene, but this is elementary school math! The AVERAGE of these (2) MPG 'estimates' is 16.7 MPG. There is a 99% chance the first 'fill' was inadvertently a few gallons short of full................

Some of the suggestions here are downright comical!!!

 

Let me clear the air about this MPG issue. First, the MPG's have been up and down over the 20-30 fills. I fuel at the same station, with the same pump, 90% of the time. I drive the same roads, 99% of the time. I check my mileage, with a pencil and calculator, every time.. If I wanted to play numbers games, I guess I could average the fuel use over the past, week, month, year, and since I've owned the truck. But, that number manipulation doesn't answer the question, WHY are the MPG's varying 3-5 mpg when driving the same roadway, under the same conditions? There's no damn way I could have a 8-11 gallon fill-up difference between trips by fueling at the same pump...(overfilling prior to trip, then underfilling upon return) Think of it this way... considering a 28 gal tank:: 28 gal x 19 mpg = 532 miles. 28 gal x 13.5 mpg (seems to be my avg) = 378 532 - 378 = 154 mile difference. if my truck really gets 13.5, and 19 is a fluke because I'm incompetent in fueling by pushing more in tank and less upon fill, then explain to me this; at 13.5 mpg it takes 11.4 gal to go 154 miles.. which is the difference shown above.. So, I stand firm, there's no way in hell there's an eleven gallon difference when fueling. That's simple math and common sense!

And, I know the following statement is comparing fruit, but of different types. How can a friend of mine's dodge one ton pulling a 48ft two level car hauler (loaded) get 16.2 mpg. (figured with a calculator, odometer compaired to gps miles for accuracy)( I know these figures are accurate, because I drove from KC, MO, to Littlerock, AR to StLouis, MO, then home, when he was injured and needed help)

My brother owned my truck before I did (I bought it at 141,000 miles), he was getting in the 17-19 category on the highway empty, and 12-13 mpg pulling a 28 ft steel gooseneck trailer loaded with cattle at 80 mph. Then I get in the 17-19 range for a short time then it drops to where it is now for no apparent reason.

Yes, I drive a truck, not a Yaris or an Accord.. I realize i'm not going to get 30 mpg, but, it's a diesel truck that's under 300 hp.. It should do better than it is...

 

I'm headed back to simple....

Going to check fuel pressure under all driving conditions. Can anyone tell me the size/thread of the fuel bowl plugs? Had to replace my fuel test gauge set due to a theft. and, I don't think I have the size needed to thread into the fuel bowl and connect the 6 ft of hose....

Going to drop the fuel tank to check the pickup screens, wouldn't be surprised if they are full of crud.
And, does anyone sell all the components to do the Hutch Mod, in a kit? Might save me time running all over town buying them individually.

Thanks

 

Without the harpoon mod - your 'fills' could totally be that far off. But I'm happy to help you chase rainbows and unicorns! (note: meant to be funny - mmmkay? I don't take myself that seriously...)

First, build a boost leak detector and look for boost leaks:




The spider-to-plenum boots almost always leak eventually. The only way to keep those clamps tight is to REPLACE them. You need these in order to use better clamps on the plenums:
Riffraff Diesel: RDP Plenum Reinforcing Inserts™

Clamps:
Riffraff Diesel: T-Bolt Boot Clamps

Make sure you don't have up-pipe leaks as well. Either of these 2 things will make a LARGE difference between loaded/unloaded MPG. Higher boost and drive pressure when towing will exacerbate the loss in MPG.

Here's the fitting for FP gauge:
1/8" NPT 90º elbow pressure port adapter.

As far as in-tank mods 'kit' - Strictly Diesel had a kit, but it was $159!! I'm sure I didn't have much more than a Happy Meal in mine including a WIX 33972 pre-filter... Clay was putting a kit together, but I don't see it on his site yet - give him a call!!

Good luck. Keep us posted!