GM Truck Club
THE PREMIER CHEVY TRUCK & SUV FORUM
Founded in 2004 ~ We're the #1 Chevy Truck & SUV Forum.
Silverado & Sierra | Tahoe & Yukon | Suburban & Yukon XL | SUV & CROSSOVER
Results 1 to 8 of 8
  1. #1

    Default Your 4.8 4x4 fuel economy..

    Hello all,

    I am new to the site but have used it in the past to help modify my truck. The truck is a 2002 regular cab 310 000kms - 192 000 miles, - step side. 4.8 auto, z71, 3:73 gears. I absolutely love the truck and it's been great to me so far.

    I just did a lot of highway driving over the last two days with little city driving. I have recently replaced the plugs and wires, fuel filter and it has a ebay air intake kit.

    I got an amazing 11.8mpg while doing driving between 60 and 70 mph over a couple long trips. Seems a little low to me..
    If anyone else could chime in with their numbers that would be great.

    I have tested the fuel pressure and it tested pretty low.. 41 psi, it does have one engine code for the evap filter being clogged.

    Thanks for any help.

  2. #2

    Default

    Have you changed out the fuel filter? I am not saying that that is causing your low MPG but, you did mention changing plugs and wires. That does seem pretty low. My 2005 yukon xl 4x4 5.3L gets between 18-21 mpg on the highway depending on conditions. My 02 silverado extended cab 2wd 5.3L consistently got 24 mpg cruising at 72mph, with a jet programer, it had 3:43 gears. What kind of plugs did you put in? I got talked into some Autolite plugs for the 2002 one time. It dropped my mpg significantly. I noticed this after one 800 mile road trip. I changed to plugs out to the AC delco that GM recommended and the next week when I did the exact same trip my mpg went back to normal. I have never had a 4.8L but those numbers seem pretty low. What pressure are you running your tires at? I know with the yukon if I run 32 psi I get around 16mpg if I run 35psi I get much better numbers

    1995 Silverado 4x4
    6" BDS Suspension Lift-3" Body Lift-Add A Leaf in rear -Trailmaster SSV Shocks-Duel Steering Stabilizer Kit -AirAid Cold air intake-
    4.56 Gears with Detroit Auburn Locker-Pro-Comp Traction Bars with duel shocks-Aluminum Skid Plate Kit-38.5" x 16.5" Mickey Thompson Baja Claws-Constant Dropping fuel gauge

    2005 Yukon XL Jet Power Programmer, Bilstein Shocks, Bilstein rear springs, Helwig Anti-sway bars, EGR Window Visors, EGR Hood Shield, Denali Headlights, Headlight harness upgrade, GE NightHawk Bulbs, White Night Rear lighting system, Russell Braided SS brake lines, PowerStop Brake pads, PowerStop cross drilled and Slotted Rotors, http://www.gmtruckclub.com/forum/sho...5-GMC-Yukon-XL
    2002 Silverado ext cab 2wd (Sold)
    2003 Yukon XL (Totaled)

  3. #3

    Default

    I am running NGK TR55 3951 V-Power Spark Plugs and I replaced the fuel filter with the plugs. My tires are 265/75/16, so a little bigger then the stock ones, filled to 50 psi. Would low fuel pressure cause poor fuel economy? Thanks for the help.

    Jake

    Quote Originally Posted by Pikey View Post
    Have you changed out the fuel filter? I am not saying that that is causing your low MPG but, you did mention changing plugs and wires. That does seem pretty low. My 2005 yukon xl 4x4 5.3L gets between 18-21 mpg on the highway depending on conditions. My 02 silverado extended cab 2wd 5.3L consistently got 24 mpg cruising at 72mph, with a jet programer, it had 3:43 gears. What kind of plugs did you put in? I got talked into some Autolite plugs for the 2002 one time. It dropped my mpg significantly. I noticed this after one 800 mile road trip. I changed to plugs out to the AC delco that GM recommended and the next week when I did the exact same trip my mpg went back to normal. I have never had a 4.8L but those numbers seem pretty low. What pressure are you running your tires at? I know with the yukon if I run 32 psi I get around 16mpg if I run 35psi I get much better numbers

  4. #4

    Default

    For some reason, the 4.8s appear to offer poorer (by 1, or 2 mpg) mileage than the slightly larger 5.3. You should be seeing around 17 to 18 driving at 65 (IMO).

    I like to change the front O2 sensors when I change plugs. The sensors will get tired and switch slower (may still be in spec, just slower).

    Tires a little bit bigger should hurt, the air pressure is good, but what thread pattern are they? The best mileage is with an almost smooth pattern, like a touring tire, the more aggressive the thread pattern, the higher the rolling resistance.
    Ray

    '09 Avalanche LTZ - Black
    '05 Envoy XL (sold)

  5. #5

    Default

    Here's an update..

    I put in a new AC Delco fuel pressure regulator, and a new AC Delco fuel pump/sending unit.

    My pressure with key on is 50 and running it is 48.
    With the vacuum line off the FPR pressure goes up to 58
    With the vacuum line on and return line blocked I get 58

    Any input would be great, thanks!

  6. #6
    Legend

    Join Date
    Feb 2008
    Location
    Red Wing, Minnesota, United States
    Posts
    3,386

    Default

    Put the factory spec plugs back in it, vortec motors just don't run we'll on anything but the ad/delco plugs, if you do a search you can find many threads on here that agree with that. I have 2 trucks with different motors from different line of motors and the same is true for both they ran like crap on anything but ac/delco iridium plugs.....
    99 K1500 Suburban LT "THE BEAST"
    Hypertech III, K&N, true dual
    285/75/16
    ___________________________
    Jason

  7. #7

    Default

    Just wondering what AC Delco plugs I should get. Thanks



    Quote Originally Posted by vncj96 View Post
    Put the factory spec plugs back in it, vortec motors just don't run we'll on anything but the ad/delco plugs, if you do a search you can find many threads on here that agree with that. I have 2 trucks with different motors from different line of motors and the same is true for both they ran like crap on anything but ac/delco iridium plugs.....

  8. #8
    Legend

    Join Date
    Feb 2008
    Location
    Red Wing, Minnesota, United States
    Posts
    3,386

    Default

    Any parts store will be able to tell you the exact number, they have changed over the years as they used to be called double platinum but now more common as iridium tip you just want to make sure you have OE plugs in it. Also check your fan shroud under the hood, they usually will show a part number on it as well, right next to the picture of the correct flow of the serpentine belt

Similar Threads

  1. 6.0 L Fuel Economy
    By islander_25_06 in forum Performance & Fuel
    Replies: 1
    Last: 03-22-2011, 08:02 AM
  2. Fuel Economy
    By Boltazar in forum Performance & Fuel
    Replies: 9
    Last: 02-21-2010, 08:01 AM
  3. fuel economy
    By juiceman in forum General Chevy & GM Tech Questions
    Replies: 13
    Last: 09-09-2009, 10:33 PM
  4. What's your fuel economy?
    By ChevyFan in forum Performance & Fuel
    Replies: 55
    Last: 04-03-2008, 08:30 AM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •