2009 5.3 DOD with AFM gets bad MPG...HELP

Discussion in 'General Chevy & GM Tech Questions' started by jscookson, Feb 23, 2011.

  1. jscookson

    jscookson New Member

    Hey Guys, I have a 2009 Silerado Crew cab with the new 5.3 DOD motor with the active fuel management system on it and equipt with the new Allison 6 speed trans. I am only getting about 9.5 mpg driving like I have a bed full of eggs. IS anyone else having issues with this?
  2. cshoule

    cshoule New Member

    Your not alone,i have a 2010 4.8 silverado crew and shes a pig. i tried driving with the tailgate off, seemed to help abit but not sure if its legal. hope someone can help. good luck.
  3. jscookson

    jscookson New Member

    LOL, thanks for the sympathy.. I've been told by my Chevy mech that if I put a new exhaust from header back I will gain maybe 1-2 mpg at a cost of over $3,000 and If I buy the programmer and disable the AFM system I might gain another 1 mpg at a cost of about $400. So for about $3500 I Might gain 3 mpg.....not sure if that’s worth it or not...
  4. 98Hotrod98

    98Hotrod98 Rockstar 100 Posts

    i seem to be suffering something similar. On the highway i get about 12mpg with fuel additives, 10 without. The truck only has 4k miles on it, so i know the motor isnt broken in good yet, but shouldn't i be getting better? I would just be glad to get somewhere in the ball park of the window sticker (19).
  5. silveradotrailblazer

    silveradotrailblazer Epic Member 5+ Years ROTM Winner 5000 Posts

    I see alot of the NBS owners with the AFM/DOD complaining about bad mileage. I would hope GM starts addressing this. My '05, 5.3, 4x4 crewcab silverado with 6" lift 35" tires and 4.10 gears gets 16-17 mpg highway and 13-14 city. I'd be pissed if I ownly got 12mpg highway in a newer truck.
  6. 98Hotrod98

    98Hotrod98 Rockstar 100 Posts

    Dealer wont even acknowledge it. They just say mileage is subject to driving habits which is out of their control, and as long as the computer isn't throwing any codes, there is nothing they can do. ( IE... we made a faulty product, and wont admit it)
  7. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    Wow, that is bad MPG.
    A stock 5.3- with stock wheels stock tires 3/4 ton no lift 4x4 should easily get 15 mpg at say 65 mph with the CC set on a level hy.

    An aftermarket exhaust won't help-waste of $$.

    You have stock tires and wheels- no heavily lugged mud type tires?
    No bigger wheels/tires?

    Now city stop and go- mpg varies.Heavy vehicle- 6500-7000 lbs easily- so 9.5 is plausible.
    Test it on pure hy driving- let us know what you get.
    What is your usual hy speed?

    Silverado's mpg is about what I would expect from someone who is trying to get good mpg- average guy maybe 2 mpg less.
    12 mpg hy is terrible - if you are driving 65 mph- about what I would expect at 75mph?

    SBC generally get good hy mpg at 60-65 mph.
    My 1998 Suburban - 5.7 216,000 miles- 1/2 ton 2wd worn street(P) tires- gets 20-21 mpg at 62 mph. The 5.3 is generally 2 mpg better than the 5.7.
    Don't spend $$ adding exhausts.CAI or any other stuff to improve mpg- won't work.
    GM must be aware of this- maybe they will do some sort of reprogram??
  8. 98Hotrod98

    98Hotrod98 Rockstar 100 Posts

    I got stock tires and only a small lift.
    I typically drive on highway 70mph. For the round trip i take once a month, it comes out to almost exactly 303miles. I fill up, jump on the highway and run about 70, that night i return doing about 65mph ( night time reduced limit ). I get home, i'm usually right under a 1/4 tank. Typically about 25gals for that 300mile trip. ( 12mpg )
    I do use cruise control, but i've tried without it too.
  9. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    Hotrod- dead on 12 mpg at 70 mph- level hy with modest lift- is too low even for a big truck with 4x4 and modest rear end- not a 4.10 like Silverado with big lift and big tires.(He gets better than an average driver with that setup- drives to get good no doubt)

    I wouldn't expect your lift to cost more than .5 mpg or so. I would expect you to easily get 15mpg at 70 mph-

    Have you checked your odometer against some known distance? I doubt it can be off very much since the ECM knows your tire height and knows how many RPMS the driveshaft is turning-.
    Any chance your brakes are dragging-tires aren't wearing funny- horrible alignment??

    Now the ethanol in the gas hurts mpg- it can be up to 15% ethanol-only supposed to cost you 3-5% in mpg but many folks claim more like 10%

    I've seen this sort of thing with other vehicles-folks getting 14-16 mpg hy with Honda Pilot-should get 22 mpg at 65mph.
    Honda would check it- no codes- say it was "just fine" but everyone else is getting 25% better mpg- so no way is it "just fine".
    Some had some luck doing some sort of "relearn" but it would revert to crummy mpg after a few hundred miles.
    Yeah, something isn't quite right, but usually the manufacturers deny deny until they come out with some sort of revision that cures it.

    Check all the obvious stuff- poor alignment- goofy odometer-dragging brakes-then bug GM until they come out with some sort of service bulletin
  10. 98Hotrod98

    98Hotrod98 Rockstar 100 Posts

    Thanks alot for your reply.

    After my lift i got my alignment done ( 2k miles ago ) so i assume thats good considering i dont feel any steering issues.
    The Odo is accurate, as i've been running the same once a month trip for years now, and the odo shows about the same as prev vehicles.

    I hadnt thought about the brakes, i'll call the dealer today and see if i can get it in for another inspection. Last time i was there getting my rattle in the dash fixed ( which they didnt fix ), and they broke my glovebox, which is still broken after 2 repair attempts. So my confidence in the dealer is rather low at this point :( ....

    Best Regards,

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