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Poor MPG. New plugs, wires next?

Discussion in 'Maintenance & Upkeep' started by cbroberts88, Aug 27, 2013.

  1. cbroberts88

    cbroberts88 New Member

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    Hey all,

    My Avalanche has been averaging around 12 MPG per tank. It's 4x4 with 3.73s, stock ride height, with Diablo 87 octane tune, and a K&N CAI. I made sure I reset the computer by disconnecting the battery after I installed the CAI. Anyways, last weekend I decided to clean the MAF sensor and change out my plugs. These were the stock plugs with 70k miles on them. I replaced them with Denso Platinum TTs (PT16TT) because I figured I'd trying something different. Next might be wires if my mileage doesn't improve much. Any other ideas? Also, what do you think of the plugs below?


    20130825_134805[1].jpg 20130825_134840[1].jpg 20130825_150400[1].jpg
    #1
  2. rileyjr16

    rileyjr16 New Member

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    Are you throwing any codes?
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  3. cbroberts88

    cbroberts88 New Member

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    No codes. I even check every once ina while.

    - - - Updated - - -

    what did you think of those plugs? Pretty dirty?
    #3
  4. rileyjr16

    rileyjr16 New Member

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    Yeah. Mine looked like that after 40,000. But my knock sensors need to be replaced. You don't drive like a bat out of hell I'd assume. Does it have the 5.3 or 4.8?
    #4
  5. McClintoc

    McClintoc Super Moderator

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    I don't think those plugs look that bad. Other than changing plugs, modern engines don't require much of a "tune up" like they used to. Change the plugs and fuel filter, clean the air filter and keep the tires aired up (go a little above the recommended air pressure on the door, maybe 5 to 10 pounds) and you should be getting most out of your fuel mileage.
    #5
  6. cbroberts88

    cbroberts88 New Member

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    5.3L. I keep the rpms under 2000.
    #6
  7. stchman

    stchman New Member

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    The plug wires on the 5.3L V8 engines are really short, so they are really easy to replace. I don't know how much they cost, but it can't be that much.
    #7
  8. cbroberts88

    cbroberts88 New Member

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    That might be the next thing to do after I take it to the dealer. It's under warranty and I want them to see if there are any recalls or TSBs applicable to it and see if they can find anything wrong with the vehicle and fix it then.
    #8
  9. RayVoy

    RayVoy Active Member

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    Fresh O2 sensors (front ones) might help. I like to change mine when the plugs are changed.

    But, the thing that impacts mileage is rolling resistance. Tire pressure, thread pattern, rubber compound, alignment. tight brake pads.

    Anything that increases the amount of power required to roll the vehicle will cut into the mpg.
    #9
  10. cbroberts88

    cbroberts88 New Member

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    brand new Bridgestone Dueler H/L Alenza filled at 36 psi approx.

    I appreciate all of the responses. Maybe the truck is just THAT BAD on gas. My 2011 Silverado averaged 16 mpg and I thought that was terrible!
    #10
  11. RayVoy

    RayVoy Active Member

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    My '09 is not as bad as yours (it does have the 6 speed tranny and 3.42 gears). A lot of city and a bit of highway will give me around 16 mpg (at least, that's what the DIC tells me).

    As I posted in an other thread a couple of days ago, I tried a speed test last week while driving in ME. 45 mph gave me the best mpg (around 25), 55 to 60 knocked it down a bit (I think it was around 20 mpg), driving at 75 knocked it down to 18. Speed makes a difference.

    I change the front O2 sensors when I change the plugs, because I've read that they start getting lazy around 80k, if this is true, or not, IDK.
    #11
  12. cbroberts88

    cbroberts88 New Member

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    Thanks for the info! I would love to get mileage like that!

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    Took the truck to the dealer today. They said they checked everything and it all seemed fine. maybe the truck is just that bad on gas. oh well. I went ahead and changed the plug wires as well.
    #12

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