Anyone with a dually and an EFI 460.???

I have a 1994 F-350 4-door dually with 117,000 miles on it. I currently get 8.5 to 9.2 mpg city, and about 10.5 to 11 hwy. I have read most of the other posts that I can find, and most people seem to get a bit better mileage. However most of the comparison vehicles don't seem to be big ol' duallys. I have not owned a dually before, only normal trucks and don't expect great gas mileage, but wonder if this appears to be the norm?
Mechanically it has a Hypertech module, Gibson stainless headers and high flow exhaust, a K&N air intake, and factory overdrive. I am somewhat neurotic, (according to my wife), about my vehicles' mechanical condition, so all things such as plugs, wires, cap, etc. are in good or new condition. Also I drive "like a grandpa" as I have been told, and tend not to have a lead foot.The previous owner took extremely good care of the truck. Computer diagnostic check revealed a bad TPS, which was replaced. All other checks were ok. Before spending money on replacing sensors "just to try it", I was wondering what mileage you other guys were getting? If this is normal, I'll live with it, but at $2.00 per gallon here, it's gettin a tad expensive. Good thing I got a motorcycle for work!

Thanks for any help.

 

What ratio gears does it have in the differential?

 

It Has 4.10's with stock size tires

 

That's part of the reason right there.

What RPM does the engine run at when doing 55-60 Mph in high gear?

 

On the freeway, at about 60 mph, with the factory overdrive on, it tachs around 2000 - 2100 on basically level ground.

 

Tlaw,
Suspect you have the same problem I have, The torque band is too high for your cruising rpm, I found I get the same mileage at 65 as I do at 80. 65=2200 rpm

I just intalled a straight uip cam gear set, and it is supposed to bring the power band down in RPM, from what I under stand, once I get the Ignition timing right I'll find out if it helps. I am going on a trip this weekend and will find out if it helps mileage at all.

This is the only confirmed way to move the power band down that I have found so we'll see if it helps, I found stock that all the power started at 2700 rpm and the gearset is suppoesd to drop it 300rpm, not Ideal but worth a try (I had to reseal the chain cover anyway)

Will let ya know what happened next week

 

For an F350 dually with 460, automatic and 4.11 gears, I think your mileage is acceptable. With all that weight, anything less than those grears will require more rpms to overcome initial inertia, offsetting any higher geared cruising gains. You'd need marked improvement to off-set the cost of gears and setting the lash.

 

yeah, for a dually, that is pretty good. My '86 (no overdrive) gets about 6.5 to 7, that is freeway, city, towing, empty...it don't make no nevermind nohow!

Most guys I know with older duallies, whether chevy or ford, get around 6 or 7.

I have recently installed headers so we'll see what it does to my mileage.

 

I have almost the same setup, minus the dually and also have C-6 tranny and no crew cab. I get 11.5 MPG on the highway at 55-60 MPH. The RPMs are higher than yours, closer to 3,000.

In my opinion, what you are getting is about normal for a truck of your configuration. Maybe given OD you should be getting a bit better than that... I don't know.

I am thinking about re-gearing to 3.55 but wonder how cost-efficient this conversion will be. Probably save 1 MPG I am guessing. Any insight on that?

 

On the gearset,
My father-in-law has a '78 f-350 w/460. When he bought the truck it had 4.11 gears in it. It got about 6 mpg city. He had 3.53 gears put in his and got about 1/2 to 1 mpg better. Not a lot of difference considering the cost, ( it was about $450 installed), but it sure made a difference in the way the engine ran. It dropped the rpm noticeably, and the engine seemed to really like that. So I would say that if you don't plan on any heavy towing, (he just tows a 22' boat), and have the money, it may add a little extra longevity to your motor, and it won't be screaming at you on the freeway.

 

I don't have a dually but I do have a 4wd with a 460 and E4OD. My driving is split almost 50/50 between city and highway and I average right at 10 MPG. So if I were to guess I would say that your mileage is normal.

 

Your mileage seem pretty darn good.

A dually will get less MPG because of the extra 2 tires on the road. You have more friction with the road, and therefore you will loose a little on economy. At least, that's what I've been told my whole life.

I get about 13 and drive in a mix of highway/city to the tune of 100+ miles a day, single axle.

 

I have checked this several times with known distances. I have a 4 speed manual tran. and a NP 205 transfer case and am running 235/75/R16's and 410's in my DANA 60 4x4 hi boy.

Where the MPG really drops is if I am driving on hilly roads-- can drop down to around 9 MPG.

I am easy on acceleration to keep my MPG up and I generally don't drive over 55MPH.

Greg