Please explain like I am a 5 year old. New Tires, Gas Mileage drop.

  1. Sorbs

    Sorbs Well-Known Member

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    You might wait for the ECM/PCM to adjust to your new setup. Modern ECM/PCM's adapt to driving conditions and your driving habits.

    Follow these steps to reset your EMC/PCM:

    1. Disconnect the battery by removing the Negative battery cable (This will ensure that any possibility of grounding the power side to the vehicle does not happen.)

    2. Disconnect the Positive battery cable

    3. Allow a five minutes to pass before reconnecting the cables

    4. Reconnect the positive cable to the battery

    5. Reconnect the negative cable to the battery

    6. Turn the Vehicle on


    The ECM/PCM parameters for all sensor calibration monitors have now been reset. It can take anywhere from a few minutes to a few days for all of the system parameters to be restored within the unit.
     
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  2. JLUin818

    JLUin818 Well-Known Member

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    is that going to work with the second battery? Do all JLs have a second battery?
     
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  3. Sorbs

    Sorbs Well-Known Member

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    The second battery is for the ESS system. Although it will prevent the vehicle from starting if dead it doesn't provide primary power to the PCM.
     
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  4. OP
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    lepcat

    lepcat Well-Known Member

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    How much did yours drop? I honestly expected a little bit of a drop but not quite as much as I got. It has been windy the last few days since I changed over. So I think I’ll get a better baseline highway and city when the wind stops.
     
  5. OP
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    lepcat

    lepcat Well-Known Member

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    Yes I’m very happy. Kept my stock suspension so the rides really nice in town and on the highway. Doesn’t walk much if at all. It was a rated tires will definitely grab a groove in the highway or rats left by semi’s. But that’s to be expected.
     
  6. JLUin818

    JLUin818 Well-Known Member

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    i havent done any serious calculations but on rubi 33s i would often hit 28mpg on the freeway with cruise control on. Now its like mid to low 20s.
     
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  7. wrangster

    wrangster Well-Known Member

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    Just a bad choice with 3.45 gears, there are graphs for tire to gear ratio.
     
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  8. wolfdog

    wolfdog Well-Known Member

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    I'm kinda thinkin' a JLU or JL Rubi with stock tires downhill with a big tailwind and in neutral wouldn't get 28mpg???? Just sayin'?

    Go Jeep!!!
     
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  9. Spank

    Spank Well-Known Member

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    I don't think the fuel economy calculations are adjusted at all to compensate for changes to the drivetrain when you adjust values such as tire size or even gear ratio. I could be wrong and maybe its different for the JL, but this was certainly true for the JK. The JK had always maintained its set range based on the stock configuration of the vehicle. My regeared '14 with 35s and 4.56s would still report the same general averages even though I was definitely getting less fuel economy in the city.

    I'm running 37s on stock 4.10s on my JL and my fuel economy numbers remain largely unchanged in the EVIC, but I know for damn sure I'm not getting 18mpg on the highway with these meats.
     
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  10. JimLee

    JimLee Well-Known Member

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    My MPG's dropped from 18.5 to 16.1 average going to 35's, it is what it is. I doubt i'll gain anything back when I go to D60 axles and 37's with 4.88 gearing, but hopefully it'll hold somewhere close to there. Would be nice if someone actually started producing an aux fuel tank for the JL, which will ironically drop your MPG's even more with all the extra weight. Oh well, can't own an offroad monster and be a gas miser, have to accept the realities.
     
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  11. OP
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    lepcat

    lepcat Well-Known Member

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    Dang. Okay. Thanks for the reply.
     
  12. wrangster

    wrangster Well-Known Member

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    Lots of jeepers here fail to mention braking with the larger heavier tires. Going to a larger brake set would be another smart choice! so what we have is : axles, gears, tires, rims, brakes etc. etc. Think I would rather go off road onto rocks and such with a Polaris and much cheaper to. Just my take on this! enjoy whatever you love to do.
     
  13. JLUin818

    JLUin818 Well-Known Member

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    i havent noticed any detriment to my braking. I also dont drive my jeep like sports car either. Upgrading the brakes is not cheap and not worth it imo.
     
  14. Dagwood

    Dagwood Well-Known Member

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    Please do, it will make this post far more entertaining.
     
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  15. Dagwood

    Dagwood Well-Known Member

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    Since it's a four door I'll start.
    When the wheels on the bus go round and round.
     
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