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Discussion Starter · #1 ·
I have a 2012 JKU Sport 3.73 gears, automatic with 2.5" lift and 35" tires. Dealer did an update flash on the ECM and now my mileage has dropped to 14.7 actual or 15.4 EVIC on dash from 17.5-18 mpg since I bought it in July. Dealer says it's the colder weather not the flash. I was wondering if this mileage dropping is happening to alot of JK's, mine has just over 4000 miles on it.
 

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Are you comparing your MPGs to when you got it, or after you installed massive tires?
 

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Discussion Starter · #5 ·
Tires were put on right away. Since new this thing has gotten 17.5 - 18 mpg all day long and I was loving it. After dealer flash it dropped to 14.7-15.4??
 

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Discussion Starter · #8 ·
I have heard of winter grade fuels dropping mileage but not this much. My Hummer H3 with 5.3L GM V8 and 34" tires got 13.9 all year round so I dont suspect its the winter blend fuel.
 

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Discussion Starter · #9 ·
Yes I have the Procal and im wondering the same thing. I did have to zero out my TPMS to zero again after the dealer flash. Speed seems right though. No head issues so far but im also wondering if this is a warning of an upcoming problem. Heading up north to deer hunt soon so I hope not.
 

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mpg is not just reduced by winter fuel. if you do a lot of highway miles, the air is more dense when it is cold, so it takes more effort for the jeep to push through.
 

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winter grade fuel? educate me please... I thought all fuel was winter grade as it doesn't freeze until -40 to -50 C.

From what I always understood, the cold makes the tires harder, shrinks the air inside and you loose a couple pounds of psi. A couple pounds low will cause enough drag to cause the increase your seeing. Have you checked your tire pressures while cold? Seriously, 1 low tire by 3-5 psi can cause a decrease by 3-5mpg on average.
 

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Winter is just a appetite for less mpg. I go from 16.5 all summer and already I'm pulling 14's now. Engine takes longer to get to operating temperature so it is not as efficient as a fully warmed up engine. Cold air is denser thus more is sucked into the engine which in turn burns more gas to compensate.
 

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I have heard of winter grade fuels dropping mileage but not this much. My Hummer H3 with 5.3L GM V8 and 34" tires got 13.9 all year round so I dont suspect its the winter blend fuel.
My Hemi Grand drops 1-2mpg for the exact same trips winter vs summer. I count on 21-23mpg highway (long haul Chicago to Green Bay round trip) in the summer and it drops to 19-21mpg on winter blends. The range of mpg is due to the better non-IL gas I get in WI for the return trip. Needless to say that fuel can make a large effect on economy and performance.

Double-check your speed/odometer calibration and then run a few more tanks from a reliable high volume gas station. If no dice there, a fuel economy hit is related to an impending head issue, FWIW. Keep an ear on it.
 

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Yes I have the Procal and im wondering the same thing. I did have to zero out my TPMS to zero again after the dealer flash. Speed seems right though. No head issues so far but im also wondering if this is a warning of an upcoming problem. Heading up north to deer hunt soon so I hope not.
Since you had to re-do the TPMS could you need to re-do the tire size?
 

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Discussion Starter · #17 ·
Just spoke with Greg at AEV and he suggested that dealer may have erased all codes before setting the new flash. Reset BFG All Terrain T/A KO's 315's with a measurement of 33.50 as measured under weight of vehicle. Hope this fixes the problem.
 

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Discussion Starter · #18 ·
Why are you guys getting the dealer re-flash?
I was not aware the dealer was doing a update flash. I took it in to replace the passenger door seal that they hacked up trying to fix the leaking into my floorboard. Now I will request no update flashes when its in for service.
 

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Discussion Starter · #19 ·
Dealer said the flash was an update to eliminate early check engine light codes that were coming on falsely. Probably the one recognizing the head issue im guessing.
 

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Discussion Starter · #20 ·
Tires are all set to 31 psi as this offers the best ride and fuel mileage so far. AEV set them at 28psi but I went with 31 psi after chalk test and ride quality and fuel mileage figured.
 
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