just for reference, i have a 97 F350 crew cab dually, 460 with a 5 speed and 2 wheel drive, if I keep it under 55 I can attain 16 miles per gallon, mods so far are the air intake and exhaust, if you take the intake air tubes off and cut the plastic bells off inside where they neck down it helps a lot, I also cut my cat off and shortened the exhaust sending it out the side before the rear end, I also took off all of my EGR system and air pump, but it was worth it to get 16 mpg

 

i cut out those air horns, and did not see much, if any difference.

 

You mentioned straight axle up front? And 4.63 gears?

Is this a utility truck, dump truck?

That is one heavy freak'n truck. I can see why it fails in the MPG category.

I had a '96 SC dually, 460/E4od/4.10 that got a solid 10 mpg daily, and 7 mpg pulling my 14K Haulmark trailer. Back then gas was CHEAP!!! (around a buck still)


Yours likely doesn't get into OD much around town(since it has to be going 35+ mph to do it). It is likely never going to get great mileage no matter what.

I can see replacing the cats with something free flowing. Don't put a Flowmaster on it, that will likely kill your low end power(though you do have 4.63 gears). I ran a Dynomax Turbo muffler on my truck with just a turndown on it(no tailpipes). Mine had the twin tailpipes and didn't have anything to replace them with when I put the muffler on it.

 

I took my truck (96 4x4 460 MT) on a road trip this past weekend. About 220 miles total. Since I rarely get it out on the highway unless I'm towing, I checked the mileage carefully. I ran at a steady 65 MPH (cruise set most of the time) and got 14.6 MPG. This was at 6000 ft elevation on a winding & hilly road. I'm sure at sea level on a straight road I could do a little better.

 

^^ does your truck have 3.73 or 4.10?

 

I believe only 3.55 and 4.10 were options with the 460. My guess is that Doug has 3.55. My truck in my sig get 14 or so on long highway trips at the same speed.

 

The truck has 4.10 gears. At 65 MPH I'm showing about 2200 RPM.

 

truck is a utility/service bodied truck. i understand that it is heavy, and is not going to be efficient, but 4mpg is rediculous

 

I think you're doing VERY well considering the 4.10s.

 

I agree-that seems awfully low. I regularly get 11 MPG flat-towing a Jeep in the Colorado mountains.

 

Something does sound wrong. Even at 10K lbs, it should do better then 4 mpg.

 

I agree with that, I was getting 8.5 with a 16,120 lb combination, and dealing with the air drag on a 5th wheel. 4 mpg is Chevy 454 levels.

 

thats what i'm saying. i'm thinking i should get alomost double what i do. the truck runs good; a little "chuggy" at idle. but runs and pulls well for a gas truck. i almost wish the truck would throw more codes than it does

 

If it's chuggy at idle, it sounds like it's a bit rich? Likely the reason why it gets lousy fuel mileage.

Wonder if you have a/few bad injectors?? dripping/leaking??

 

that crossed my mind too. the truck does make an awful lot of "exhaust" at idle. not smoke, but just "exhaust". like what comes out of the tailpipe in the winter when its cold and you first start it; only i get it when its 70* when the truck runs for the first 5 minutes. ive never had another truck do that.