muleyman

i just bought a 98.5 24v with 68k on it about a month ago. after calculating my mpg 3 times i got 13.04, 13.84, and 13.4. i had a fuel pressure test done and it was 14-idle, 8-wot. i changed the fuel filter that day also. the dealer says the truck is running great. obviously something is wrong. im getting this on hwy miles too(55mph) i run 285-75-16's, and also a camper shell. they serviced my tranny also.

what could possibly cause such poor fuel milage??

when i fill up i stop after 1st click. could my calculations be off because im not truely getting a full tank??

please respond
muleyman

RickCJ

Is your speedo set for the bigger tires?? That would make your mileage low.

phox_mulder

Yes, you never know how full you are if you let it click itself off.
Only way to know for sure is to fight the foam till you can see fuel in the neck,
then you know to fill it to that exact spot next time.

Has your speedometer/odometer been corrected for the bigger tires?
They came stock with 245's, might have had 265's as an option.
55mpg will actually be more like 60mpg with the bigger tires.
You will be traveling further than your odometer says as well.

Also, what rear end do you have, 4.10 will get worse milege than 3.55.

My 2002, 3.55 rear, auto tranny, 315/74R16 tires, corrected odometer gets 14mpg average.
Best mileage is at 55-60mph, drops like a rock after that.


phox

muleyman

will the tire size change the odometer though? im not sure if the speedo and odo. are in relation?

ill fill up tonight and run a 100mi. and check it again.
any other suggestions would be appreciated.

muleyman

Shovelhead

Speedo & Odo use the same signal feed.
If one's off, the other will be too.

Taller or Shorter tires will cause inaccurate readings.

dctoner

Muleyman: looks like we have the same truck if yours is the QC.

I would definately have your Odo matched to your tires! Mine has the stock size tires. Before my Lift Pump and Filter, I was getting 15mpg if I was light on the throttle. Now I get 16.6 around town and 19.7 on the highway.

good luck.

BIG&BAD

try changing your air filter
i've heard that can make a difference

mpfireman

He will run at 70 MPH,at 2000 RPM with the 3.55 rear end. I am not sure what the 4.10 will do at 2000 RPM? But with the bigger tires, and the 3.55, the spedo should read about 72-73 at 2000 rpm.




98.5 Quad cab, 2500HD series. 3.55, rear, 265x16 Steeltech tires, line X, Full flares,

Shovelhead

My 4:10s with stock 215 tires turned ~62MPH @ 2000RPM.

I'm now running 235s and I know my speedo & Odo are off.

Ed

muleyman

i did a mile check on the way home from work today and all 3 times i came up .1 of a mile off on my odometer. i just picked up my afe and will be slapping that on tonight as well. i know i can do all these mods and pick up a mile here and there, but i shouldnt have to. ill go in and get my computer reset. see what that does.

muleyman