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Old 11-14-2012, 02:26 PM   #1
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Angry Fuel mileage dropping???

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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Old 11-14-2012, 02:28 PM   #2
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winter grade fuel does drop mpgs or fuel economy its just a question of how much.

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Old 11-14-2012, 02:29 PM   #3
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Are you comparing your MPGs to when you got it, or after you installed massive tires?
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Old 11-14-2012, 02:30 PM   #4
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and youre lucky to be getting that good of a mileage. mine is getting 10-12mpgs
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Old 11-14-2012, 02:31 PM   #5
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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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Old 11-14-2012, 02:32 PM   #6
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Any head issues?
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Old 11-14-2012, 02:33 PM   #7
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Did you use a Procal to adjust for the larger tires? Could the dealer flash have wiped out that change?
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Old 11-14-2012, 02:37 PM   #8
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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.
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Old 11-14-2012, 02:40 PM   #9
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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.
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Old 11-14-2012, 02:42 PM   #10
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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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Old 11-14-2012, 02:43 PM   #11
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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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Old 11-14-2012, 02:50 PM   #12
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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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Old 11-14-2012, 02:54 PM   #13
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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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Old 11-14-2012, 02:57 PM   #14
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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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Old 11-14-2012, 02:59 PM   #15
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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??
Why are you guys getting the dealer re-flash?
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Old 11-14-2012, 03:03 PM   #16
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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.

.
HowStuffWorks "Summer-grade versus Winter-grade Fuel"
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Old 11-14-2012, 03:17 PM   #17
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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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Old 11-14-2012, 03:21 PM   #18
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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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Old 11-14-2012, 03:23 PM   #19
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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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Old 11-14-2012, 03:26 PM   #20
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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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Old 11-14-2012, 03:36 PM   #21
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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.
sounds good, have you double checked them since the problem started to be sure none are low?
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Old 11-14-2012, 03:37 PM   #22
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I had no idea... thanks for the link!
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Old 11-14-2012, 03:55 PM   #23
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Yes I have checked them all at 31psi. Im guessing it is the dealer cancelling out the AEV calibration before they flashed the ECM.
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Old 11-14-2012, 04:01 PM   #24
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Hi everyone. I have a '12 JKU. I got it new last October ('11). I have 30000+miles on it. When it had 9000 miles I had to have a header replaced. Runs better since then. I typically get 19-21 miles/gal. When I drive on the hwy I get around 21-22. My problem is that all of the sudden I've been getting around 15 miles/gal and I have NOT changed my driving. In fact when I saw the milage go down, I started to drive even slower and tried to keep it down. I read someone ahead of me on this post say that the dealer said it was the colder weather? Is that what's going on? I have a hard time believing this because I had it last year and my milage was fine EXCEPT before I had the header replaced. It got better afterwards.
Any thoughts?
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I posted this on a different thread too. Any help would be appreciated. I'm taking it in the shop tomorrow to check for a water leak above the passenger door. I have water in the floor boards and on the seat belt when it rains hard.
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Old 11-14-2012, 06:00 PM   #25
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Has anyone tried the older trucker method of putting a piece of cardboard over the front grill to see if it makes any difference? I know it would be ugly and all, but I have heard it may help with gas mileage because your engine warms up faster and stays warmer longer between trips and it keeps the cold wind out. I don't know how true it is on Jeeps vs trucks though. I notice a 1-2 mpg drop in winter usually.
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Old 11-14-2012, 06:07 PM   #26
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My 12 jk with 3.73 6 speed was getting 20 mpg all summer.. Now I'm down to 19 since it got cold! All stock, same driving as before..
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Old 11-14-2012, 07:09 PM   #27
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If you are in an area that requires ethyl alcohol blended gasoline to reduce emissions, understand that alcohol has less energy per volume [BTU] than gasoline, thus the engine has to work harder and burn more fuel to achieve equivalent performance.
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Old 11-14-2012, 07:17 PM   #28
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Has anyone tried the older trucker method of putting a piece of cardboard over the front grill to see if it makes any difference? I know it would be ugly and all, but I have heard it may help with gas mileage because your engine warms up faster and stays warmer longer between trips and it keeps the cold wind out. I don't know how true it is on Jeeps vs trucks though. I notice a 1-2 mpg drop in winter usually.

Truckers blanket their radiators for increased thermal efficiency, not for fuel consumption. Physically blocking a radiator makes the Diesel engine run hotter for the heater.

Gasoline engines won't benefit, except to warm up quicker due to a restricted radiator. A remote start option will do the same thing for a Jeep.

Both tractor trailers and Wranglers are horribly un-aerodynamic and increasing the physical restriction isn't going to help mpg.
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Old 11-14-2012, 07:47 PM   #29
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Do not put a piece of cardboard in front of your radiator. It will not help with any kind of significance. A Diesel engine gets more efficient as it gets hotter. A gas engine blows up as it gets hotter.

The only benefit you will get from something blocking your grill is that you will make air pass around your jeep instead of into the engine bay. This in essence makes it more aerodynamic, but will cause more problems for you in the long run unless you have a way to remove the blocker when it gets hot. The new dodge is going to have flaps in the grill that will close when the engine is going and open when it needs the extra airflow for cooling.
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Old 11-14-2012, 08:31 PM   #30
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I've seen this debated on all the auto forums I use. As brought up here winter fuel and drop in tire PSI seem to be valid points people seem to agree on.

One more is the cold start mode most modern engines seem to have. Until the thermostat reaches normal operating temperature, ECU's will run a generic tune which does not use feedback from the MAF and 02 sensors. This tune is usually richer than the one that kicks in once operating temps are met (I assume because the a/f ratio is not controlled by the ECU the manufacturers play it safe by keeping it rich.) People who drive short distances around town will see the biggest MPG hit in cold weather.

Of course I don't actually own a Jeep yet so I have not dug into the specifics of how the engine management works. I'm merely in the market right now...soon enough.

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