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5.3L with active fuel management ~ Getting Terrible Fuel Mileage

Discussion in 'GM Powertrain' started by mxracer919, Sep 13, 2009.

  1. mxracer919

    mxracer919 Rockstar

    I recently traded back in june for a 2009 silverado z71 with the 5.3l and active fuel management. I love the truck, but it is getting terrible fuel mileage. I have been averaging 13 in town and like 15 if i am lucky on the highway. My last truck with the 4.8l averaged atleast 18 on the highway without AFM. So here is my question, how do i even know if it is working, anyone know? I dont have the model that has the DIC(driver information center) that shows current mpg and such.....any ideas? I have considered putting exhaust on it so that i will atleast be able to hear it when it switches to 4 cyl mode. Just sucks when it stickers at 14 and 19, and says with reasonable driving habits can expect up to 23 mpg on the highway.
    Last edited: Sep 14, 2009
  2. s5belford

    s5belford Epic Member 5+ Years 1000 Posts

    I have an 09 with the 5.3 and AFM, I don't have the driver infor center either and the best gas mileage I've ever seen was about 19 on the highway with about 14-15 in the city. I have an exhaust on my truck and it is nice being about to tell when it drops down from 8 to 4 but at the same time it sounds like crap, my only suggestion is a tonneau cover and I don't regret putting on the exhaust if that help you at all? good luck!
  3. mxracer919

    mxracer919 Rockstar

    So how bad does it sound? I would do a tonneu, but I ride motocross so I have a bike in the back of my truck atleast once or twice a week. What kind of exhaust did you do? I did a cherry bomb pro muffler dumped under the bed on my 4.8l about two weeks before i traded it......it sounded good, and was cheap too! bought the muffler off of ebay for 50, and had it installed for 50.
  4. s5belford

    s5belford Epic Member 5+ Years 1000 Posts

    it doesn't sound too bad, don't really notice it unless I'm on the highway and I'm the only one hearing it, and if anyone else in the truck they don't usally know enough to hear it. It sucked at first but now its kind of nice being able to tell when it drops down to the 4. As far as the tonneau goes they are super easy to just roll up for putting your bikes, quad, etc in there. My exhaust is the flowmaster 44 knock off, and I just got the muffler because I haven't any duals that I really like and like how the stock dumps out so when its running 8 it sounds real nice, I spend $125 at the local muffler man, overall I'm happy with it. let me know if you have any other questions
  5. ahmitchell1

    ahmitchell1 Rockstar 4 Years ROTM Winner 1000 Posts

    Im glad to get 13-14 my old dodge got 10-11 when i was being nice to the pedal
  6. 2ToNe04

    2ToNe04 Epic Member 5+ Years 1000 Posts

    afm mostly comes on highway driving where speed is steady.

    i might be wrong.
  7. mxracer919

    mxracer919 Rockstar

    Yeah i figured that. Does anyone that has the DIC have any tips for the speeds at which it works the best? 65? trying to milk a little more mileage out of it. Just did the first oil change yesterday and went with the 0-30 mobil 1 fuel economy, that usually gets a mile or two per gallon.

    So.......any tips would be nice on driving speeds from you other guys with afm and the dic so i know what speeds to shoot for when i am out on the highway, thanks!
  8. ahmitchell1

    ahmitchell1 Rockstar 4 Years ROTM Winner 1000 Posts

    I just went a drove the tahoe it seemed to only switch when i didnt touhthe gas at all and at and speed then right when i touch the gas itswitched back.
  9. ahmitchell1

    ahmitchell1 Rockstar 4 Years ROTM Winner 1000 Posts

    Then again i never went over 70
  10. ChevyFan

    ChevyFan Administrator Staff Member 5+ Years 5000 Posts

    Did anything else change if how you drove between the two trucks? hauling more or less? Driving further? Did you move to a new location and on different roads (hills vs. flat, etc)? Are you in heavier traffic than before?

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