So I bought my cummins knowing they are THE boss at mileage.. my old psd 6spd 2x4 got 20mpg city, 18mpg city when harping on it.

My cummins is getting 11mpg when driving very moderately, and 19.3 mpg highway driving easy also.

The fuel filter hasn't been changed in about 3 years (last owner never changed it and owner before that didn't change it in the 2 years he owned it), so I'm HOPING its a bad fuel filter. Also, the intake is very dirty.. plus, with 256k miles I'm thinking the cat is clogged. Hopefully thats where my bad mileage is coming from, since I'm changing the f-filter, doing my bhaf, and doing a 3" straight pipe this weekend. But seriously.. 11mpg babying it? Ouch. You guys think the things I just mentioned are where the issues lie?

 

I think you just answered most of your own questions. Change your filters and lose the quarter-million-mile cat and report back. My truck HATES even slightly dirty air filters when it comes to fuel mileage.

It's really not fair comparing a 3/4-ton 4x2 with a 1-ton dually. Lots more weight, wider body and 2 more tires on the ground. It all adds up to increased wind and rolling resistance. Got those tires aired-up to where they should be (70-80 psi max)? Is the Dodge a 4x4? What's the axle gearing?

 

quarter million mile cat. That had me chuckling. But you think that could be the issue? The things I mentioned?

 

Absolutly!

 

Ok good so by the end of this weekend I hope to report in with earth-shattering fuel mileage! hehe.

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Also I've heard that AUTOMATIC cummins 4x4's get 18mpg city, so I'll be damned if my granny driven 2x4 5spd cummins cant get better! Yes I realize that it's a lot bigger, but still. This is nowhere near where it should be.
The truck has 3.55 gears, and as far as airing up the tires I cant find the damn valve stems on the drw's?? How do I air them up? Because I'm fairly certain the aren't 70-80psi...

 

Give it some more timing. 15* will do wonders.

 

Ya trust me I'm working on it, but I need to find somebody that knows wtf they are doing and somebody that has a kit

 

Easy to do. Snap On has the kit "SP500" for around $165.

 

No - thats kit is around $250

 

My old '97 5-spd Dually got a best of 19mpg on the first two tanks of fuel after I bought it. I changed the fuel filter, fuel strainer screen, added the bhaf, and straightpiped it and the fuel mileage jumped to 24mpg. It got better as the mods came, but it averaged 22mpg city & highway combined.

On the truck in my sig, which I've only owned for about 2 weeks, it got 20mpg on the first tank bone stock. I changed the fuel filter, fuel strainer, engine oil, gear oil, flushed transmission/power steering/brake fluid, changed the belt...got 23mpg. BHAF goes in tomorrow...straight pipe in the next couple weeks, hoping to gain another couple mpg or so. This was on daily driving, 75% highway, 25% city.

I think you'll see a very noticeable increase after this weekend.