Poor Gas Mileage

Discussion in 'KJ General Discussion' started by mtbspm, May 7, 2019.

  1. mtbspm

    mtbspm New Member

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    Hello, I'm sure it's been covered, but in a quick search I can't find the answer I'm looking for. I've got a 3.7 Liberty with the auto trans and in about a year of owning, haven't gotten above 15mpg more than a couple times and those only on road trips.

    I've changed, spark plugs, air filter, O2 sensors, and all fluids. What else can be a cause of mileage issues? I know these aren't overly efficient but consistently getting between 14.5-15mpg seems a bit off.
     
  2. CherokeeLiberty

    CherokeeLiberty Full Access Member

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    Is it all stock? Any lift or big tires? When you take your foot off the gas to coast down a hill, does it maintain speed well or slow down quite a bit?
     
  3. ltd02

    ltd02 Active Member KJ Supporting Member

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    What year is it (should add some info to your signature)?

    My 02 was pretty bad like that but the 05 gets around 21-23 routinely on the highway (I've gotten close to 24 a few times). About 17-19 mixed use.
     
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  4. tommudd

    tommudd Moderator Staff Member Moderator

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    What kind of spark plugs did you use? Plus air filter and sensors, what brand of each
     
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  5. mtbspm

    mtbspm New Member

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    My Jeep is a 2004. All stock and at 98000 miles.

    It doesn't seem to loose speed coasting downhill, but in Kansas I haven't done much of that either.

    As for brand parts, I used Delphi O2 sensors, FRAM air filter, and NGK plugs.
     
  6. inflaymes

    inflaymes New Member

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    I have THE SAME issue! New NGK O2 sensors, new NKG Plugs, Amsoil oil and filter, K&N air filter. I do have larger tires (only by 1 inch though). I'm getting 13.8 mpg in town...
     
  7. uss2defiant

    uss2defiant Full Access Member

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    buy a car
     
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  8. LibertyTC

    LibertyTC Well-Known Member Staff Member Moderator

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    Gas here is $8 per gallon & I get about 13 in town 16 on the highway with a tailwind.
    It is a heavy little jeep that get's up & goes well. Takes me home safely in winter.
    Hauls the boat w/fishing, camping, and I certainly did not buy it for the gas mileage!
    I feel safe in it, it's lifted and is about as aerodynamic as a brick house..:)
    Sorry about the only thing I can offer is remove all unnecessary weight, add 4 extra lbs of air in tires and...
    [​IMG]
    A free sticker for you!
     
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  9. wycowboy

    wycowboy New Member

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    I have an 06 with the 3.7. I have Autolight platinum plugs, a Fram air and oil filter and Walmart store brand synthetic 5w30 oil. No idea on the O2 sensors, probably still factory at 168,000 miles. Yes, I know they need changed and will be this summer, with NGK most likely. I get about 14.5-15 in town and almost 20 on the highway. Try changing the coolant temperature sensor. It acts sort of like a choke on a carbed engine by letting the computer know what the temperature of the coolant is so the computer can adjust how much fuel it lets in the engine. Their are other sensors that help with this too but the CTS and the O2 are the main ones in my opinion.
     
  10. CherokeeLiberty

    CherokeeLiberty Full Access Member

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    That seems normal for in town.
     
  11. HoosierJeeper

    HoosierJeeper Gold Supporter/Admin Staff Member Administrator

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    Any brakes sticking?
     
  12. JasonJ

    JasonJ Full Access Member

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    ONLY an inch larger is a significant difference.

    Meh... depends. Stop go, stop go, stop go... heavy right foot .. sure. I drive "normal", coast a bit to red lights (not in a hurry to get there just so I can stop abruptly), and I routinely get much better than that in town, 03, 145k miles, NGK plugs, basic paper air filter, OE O2 sensors, 29.6" tires.

    Honestly, how aggressive is your driving? When my wife drives my Jeep for a while, fuel economy drops EASILY by 2-3mpg. I get 18.5mpg mixed city/rural highway (55mph) ... sometimes a bit above 19. When she drives the same routes, it's tanked to 15.5-16mpg.
     
  13. mrlavalamp

    mrlavalamp Full Access Member

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    Driver makes a HUGE difference in your MPG.

    If you never push the pedal past 30%, you will get better mpg (but you will also be slower than molasses off the line/in traffic).

    Most drivers tend to use the gas pedal as an ON/ OFF switch, its either 100% or close to it, or they are off the gas and on the brakes. This is an expensive way to drive.

    With my mods and tires, plus a rola rooftop basket not mentioned in my sig, i get 12 to 15 depend on how I am behaving and city vs highway. Usually in the lower end of that though, and if I am having a "bad" day and flooring it off the line, I can get it down to 10/11.
     
  14. wycowboy

    wycowboy New Member

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    My wife gets way worse mileage than me too. She uses more throttle and brakes later then complains about mileage.
     
  15. mtbspm

    mtbspm New Member

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    Driving habits are fairly moderate, not too aggressive but not crazy mild either. I've tried to baby it for a couple tanks to see if there was any difference, and its really made no difference in how much fuel is used.

    I don't think that there are any brake stick issues either. I also never get anything over 17 on the highway.

    And for the comments saying to "get a car", I don't care to have crazy good mileage. I just want it to be better than a full size truck.
     
  16. tommudd

    tommudd Moderator Staff Member Moderator

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    15 is average for my 04 with 32s/ 4.10s / 4.5 inches of lift lots of other extra weight when pulling my loaded 6X10 enclosed trailer . That was moving the wife to North Carolina from Ohio through WVa and Virginia

    on the highway with it 20 is easy, 22 at 75 MPH is average
    The 03 does a little less, 31s/4.10s 2.5 inches of lift, averages 20 at 75 on the highway through mountains . Never check in town, too much fun punching it from lights LOL
    The 05 does the best 22-23 easy but its all stock pretty much
    all 3 have NGK coppers, stock air boxes with Napa gold filters , Mobil 1 syn oil etc
    Oh and on ramps etc , they all hit the rev limiter every time
    Not sure about yours, but none of mine like to be babied
     
  17. J33Pfan

    J33Pfan Full Access Member

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    Check the PCV and all their hoses. Buy Mopar PCV.

    are your brakes dragging?

    too much junk in the back?

    Low tire pressure?

    do you feel the trans slipping?

    usually the operator has a lead foot.
     
  18. inflaymes

    inflaymes New Member

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    I have a car. A pristine 2014 370z Nismo.

     
  19. tommudd

    tommudd Moderator Staff Member Moderator

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    Stop babying these things , they like higher revs , taking off slowly, keeping it under 2000 RPMs etc is just dogging down the engine.
    Don't trash them, but you can run them harder and not cause any ill effects
    My 04 I bought new , always took it to the rev limiter at the very least one time a day from day one, and always got good mileage,
    the 03 was owned by an older couple so broke it in a bit , but with 4.10s and 31s it goes to the higher RPMs as well daily
    Anything under 50 OD is shut off as well , where I live now I mostly have semi paved county roads and 2 lane state hiways which are crooked, curvy, etc and still easily get 18-19 on them.
    I have an 6X10 enclosed and a 5X8 home built trailer with 2 foot high sideboards running 31 inch tires that get pulled on a regular basis and if I got 12-13 MPG when pulling them it would be getting checked out right away.
    Good maintenance, NGK copper plugs every 28-30,000, PCV, oil, everything lubed etc does wonders

    As far as the comments about extra weight, sure it will somewhat, BUT that is why you regear, its why you do regular maintenance
    as stated before , my 04, 4.5 inch lift, 32s, 4.10 heavy aftermarket front and rear bumpers, kilby gas tank skid, skid row and Matrix skid plates, RL roof rack and rock rails , enough tools to rebuild a KJ, spare parts etc and always got 21-22 easy at 75 plus on the highway.
     
  20. mtbspm

    mtbspm New Member

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    Thanks tommudd, those were the kind of numbers I was expecting to see. What interval do you expect for PCV replacement? Also would I stand to benefit from ignition coils?

    I don't feel any dragging brakes, I don't have anything in the Jeep on a daily basis either.

    Again, I know I'm not going to get the mileage of a new Civic. It just seems that it should be better than it is.