ok folks. my truck is officially driving me nuttier than squirrel droppings!!

the 02 runs perfect. starts rite up no matter how cold, no romps anymore with the synthetic oil, no black smoke out of the exhaust.

6637 air filter, and a 4 inch exhaust. 16 lbs boost, flickering between 15 and 17, at full throttle .
373 gears, 265/75/16 tires, overdrive is on, and the front hubs are unlocked.
no matter how i drive this thing, i can only get 11-12 mpg in town, and 14 mpg max on the highway, 130 mile trip, with the cruise set at 65 mph.
these numbers are with the overhead console, and also doing the math; 245 miles divided by 21 gallons of fuel =11.66666 mpg

and those numbers are not correct either, cause today with the GPS unit in the truck, i noticed that when the GPS says 65, the speedo is reading 69.

i constantly hear everyone saying these trucks get 17-20 mpg.
what the heck is wrong with this thing??

or is everybody just lying about fuel mileage, and this is as good as it gets?


don't get me wrong, i love the truck, and put 13k miles on it in the past year, and only twice went more than 25 miles from home.
it is a keeper, and no matter what the mileage it gets, it is here to stay, like the 88. i am just wondering if something is wrong with it.

 

For a 4wd auto, I would think 17-20 would have been on the LSD fuel. Expect 1 - 1.5 drop for ULSD. Drop a little more for winter blend you're running now, but you're still low.

The hubs may say they're unlocked, but have you manually checked to make sure they really are? Sounds like you're speedo is off farther than mine. My truck speedo says 67 when I'm doing 55. Have you calculated MPG based on mileage according to the GPS?

Fuel filter in good shape? Where do you buy fuel? Try switching stations. There have been several threads here about some stations selling lower cetane fuel and mileage taking a dump with the "cheap" fuel in town.

 

I was getting (consistently) 18-19 mpg with pretty much the same mod's and 37's.... but it was that way since I bought it so I'm not sure what the stock mpg was. Now with 38's I'm getting 14-16 but I drive all hwy... a long way.

 

Clean the Exhaust Backpressure sensor/tube so you can mark that off your list for possible causes of poor mpg, while you narrow it down.

 

something must be wrong my dually does a good bit better

 

boost seems off. might want to check your boots.

 

The highest I have gotten out of mine is 15.98, I am normally around 14 but I have a lift and oversized tires. I have really only heard of the 2bys getting really good mileage.

Do you have any boost leaks? How old is your fuel filter?

 

And something else to consider. If you're not going more than 25 miles from home, you're probably not doing a lot of highway miles. The diesel is most efficient when it's up to full operating temp holding a steady speed.

If you're doing a lot of stop and go driving, and you're tach is going over 2,000 rpm's while you accelerate, that can explain the poor mileage.

 

Exact same boost numbers,gear and tires as I. I was going to do 6637 and 4" exhaust also but now it got me thinking. that is the only difference other i dont have 4x4. i don't get that low of GPM pulling my 10klbs 5th wheel. Around town empty i get 17-20. All they home from florida(empty,well had about 200#s in the back) i was getting 22-24.5 consistently. 1600 miles.cruise @68mph 2000rpm Not sure on how to help yea but i am also curious because my dads is somewhat like yours but his is slightly better still.

My gps matches up pefectly to my speedo

 

You boost doesn't sound right at WOT, mines at 24-25 when i mash on it and the engine light comes on the dash, SES i guess. My mileage dropped off bigtime since the winter blend, highway 15-16 with a very very light foot.

 

ok, what, where, and how??

that is on my list of things to do.
i need to get a pvc cap and make a "pressure test cap"

the 14 mpg was with a full tank, trip meter reset, and cruise set at 65 mph for 130 miles. it is currently reading 14.1 mpg, after 131 miles.

 

Had it always gotten poor mileage or just now in the winter?


Summer with a heavy foot, 4.56s and 38" tires I get 13-14mpg around town.....mostly in the 75hp setting of my TS chip.

 

no tuner here, all stock except for the air filter and exhaust.

 

ebpv clean Welcome to guzzle's Exhaust Backpressure Sensor Cleaning Maintenance Web Page

 

yup. the mileage has always been this lousy. the new fuel filter did nothing.
the only thing that made any difference was ford switching from dino oil to synthetic.
i get the oil changed at the dealer, cause it costs about the same as if i do it myself, and i don't have to get rid of the old stuff