What The heck is wrong with my MPG!!!

Discussion in 'Performance & Fuel' started by Z71FTW, Aug 8, 2011.

  1. Z71FTW

    Z71FTW Rockstar

    okay so ive added a Cold Air Intake, Hypertech Power Programmer, and fuel injector cleaners on multiple occassions. so i just took a trip to dallas and have been recording my fuel purchases on an app for my phone the best in city ive gotten is 12.22 mpg and on my dallas trip its like 190 miles or so all highway and i cruised between 70 and 80 miles per hour and when i just filled up i got 12.47 miles to the gallon why is my highway miles per gallon so close in comparison to my city i dont understand!!!????:grrrrrr:
  2. stephan

    stephan Rockstar 4 Years 5000 Posts

    The 70-80 MPH on the freeway could be part of it. Lots of wind resistance at those speeds, & WR kills MPG
  3. LSU truckman

    LSU truckman Rockstar 100 Posts

    Another thing is that almost all gas stations are using 10% minimum ethanol blended fuel. My 2000 silvy with a 5.3 and 3:73 rear axle ratio lost about 3 to 4 mpg when I use ethanol blended fuel. I have to fill up with 93 octane nonethanol blend to keep my highway milage around 19 to 20 mpg with in town about the 15 to 16 mpg range.
  4. Z71FTW

    Z71FTW Rockstar

    well shoot maybe ill tail a semi then haha get rid of that wind resistance on my way home,
    before my trip to college ill fill up with the good stuff and see what happens but that means re-tuning my truck but it doesnt take too long.
    thanks guys
  5. stephan

    stephan Rockstar 4 Years 5000 Posts

    Drafting behind a semi will show you some excellent gains, but unfortunately will get you tickets. Where do you have it tuned now? Towards the HP performance side?

    **good point by LSU about the ethanol percentage. Every time I do smth to improve my MPG, they add more eth % & my mpg stays static. Mo fos have it up to 14%-15% here now.
    Last edited: Aug 8, 2011
  6. Z71FTW

    Z71FTW Rockstar

    well yeah kinda i guess idk, i used the hypertech set it for regular fuel put rpms at 6100 and did +3 for 1-2, +10 for 2-3 and 3-4 i think and firmed up the shifting and i think thats all it asked for
  7. stephan

    stephan Rockstar 4 Years 5000 Posts

    I'd leave it set for regular fuel then, & leave your shifts set at firm (that's a good thing). There won't be any MPG gains setting it for hi-octane, plus you'll just be paying more to begin with. Force yourself to drive 65 on your next highway trip (difficult to do, I'm always creeping up there), but my MPG drops from 17 @ 65, down to 13-14 when I hit 70-75
  8. Z71FTW

    Z71FTW Rockstar

    yeah ill try for the 65 but man i hate being stuck behind ppl i have the need for speed haha which is funny bc i drive a truck and its in no means a sports car
  9. sstoner911

    sstoner911 Epic Member 5+ Years 1000 Posts

    I have a 2008 Sierra with the 4.8 Vortex. I use a custom tune, sort of, its a real basic tune with HP Tuners. I added, shorty headers, CAI, 4.11 gears, and I get 14 in town and 16 on the freeway.

    I usually do 82-84mph between Tucson and Phoenix. I got almost 17mpg from Tucson to Los Angeles a few months ago.

    I know Mythbusters said there was really no change with a bed cover, but I did see a slight improvement with mine.

    PS - I just recently got a Hypertech Max Engery cheap off craigslist mostly for Diagnostic Trouble codes, but I did load the regular fuel tune just to see what happens....so far about the same.
  10. Ethan

    Ethan Rockstar 100 Posts

    It's also illegal, it's called speeding. I-35 in that area is 65-70 mph the whole way.

    Trucks get the best gas mileage at 65 mph, don't care what anybody says, they are geared to get the best at that speed.

    When you put the cold air intake on, did you relocate the Mass Airflow Sensor into the intake, and reprogram the computer to accept the new air intake? Sometimes with the more advanced OBD 2 systems, you have to reprogram the computer to see the air intake and not adjust for it, it sees more air coming in, and thinks you are gunning it, so your TPS sensor and MAS sensor have conflicting data, and it messes with the PCM.

    That's my best guess from my experience. I don't know if I'm right.

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