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  1. #11

    Default

    I put some Sea Foam in last night. Now averaging 16.7 MPG in the city. I have a long drive to class tonight so I will see how it does on the freeway

    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)

  2. #12
    Legend

    Join Date
    Jun 2006
    Location
    River Ridge Louisiana-4 miles W of New Orleans-didn't flood-water stopped 800 yards away.
    Posts
    1,612

    Default

    4mpg- HUGE difference just from AC use.
    Any chance the prevailing winds were different?
    Of course a this should balance out in a roundtrip
    But maybe not-perhaps the wind switched directions on the return trip.
    I would check prevailing winds-you did the 1st trip in a different season -right??
    4mpg- too much for just AC use.

    Another possibility- are these mpg numbers 22 vs 17.9 the NAV readings or actual distance over gallons pumped in?
    I wouldn't expect the NAV to change over time like that
    BUT if you did actual measurements- distance over gallons pumped in
    Small differences in tank filling-say 1/2 to 1 gallon more filled-can make a HUGE difference in calculated mpg- especially on short trips 150 miles or so??

    Well just some ideas- 4 mpg- the truck still runs well and you are still getting good city mpg
    Makes me think nothing wrong with truck-and you don't have any codes
    Maybe winds maybe just a filling difference maybe AC use maybe just an unlucky combination of winds AC filling difference(if you weren't using onboard mpg gauge)

    No codes- still running well -same city mpg- means nothing wrong with truck
    Wind AC filling difference "bad gas" lower octane than claimed so less advance possible hurts mpg

    Pure guesses of course-post your next trip-curious about anything to do with mpg-I'm a mpg nut- mild hypermiler-98 Suburban(very good -21mpg- pure hy mpg-city 12-13 mpg wife kills my city mpg) 2006 Prius
    Charlie
    1998 suburban-
    1/2 ton

    199500 miles
    River
    Ridge,LA

  3. #13

    Default

    ok, time resurrect an old thread. My highway mpg is staying at 17-18. I was getting 19-21mpg. Here is the odd thing, my city mpg is at 16-17mpg with a light foot. So, my city has stayed the same but, my highway has decreased. No new mods. Any new ideas on this? thanks guys.

    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)

  4. #14

    Default

    Tire pressure change due to colder weather? Winter fuel mix finally arrive at a fuel station near you? Time for a tune up? Observer error?

  5. #15
    Legend

    Join Date
    Jun 2006
    Location
    River Ridge Louisiana-4 miles W of New Orleans-didn't flood-water stopped 800 yards away.
    Posts
    1,612

    Default

    I'm with Surreal
    fuel changes- tire pressure- just some fill to fill variation
    BUT in the winter MPG goes down-but usually city mpg goes also
    1998 suburban-
    1/2 ton

    199500 miles
    River
    Ridge,LA

  6. #16

    Default

    Try adding some octane booster to it and see if gets better. Also, with the colder weather the engine will utilize more fuel until it reaches running temp.
    2009 Chevy Silverado 2500HDLT 6.0L w/ Towing Package, Dick Cepek GM8 Rims, Dick Cepek FC II 33X11.50R17,RKSport Ram-Air Hood(Functional), Lazer Lite Aluminum Tonneau Cover, Road Armor Stealth Bumper, PIAA Lighting, Diablo Trinity Tuner, Diablew Custom Tune, BullyDog Cold Air Intake, American Racing Headers w/highflow cats, Corsa Performance Sport Exhaust, Custom Striping, Black Bowties front and rear, Fuel Grille Inserts, Recon Headlights, Readylift Shocks, Readylift Upper Contol Arms, 2" Blocks in the Rear..

    Future Plans: HD Tie Rods, Under hood upgrades, Crower Camshaft and possibly electric fans.

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