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Old 03-12-2014, 03:29 PM   #1
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Something seems off - 10 MPG?!?

Hey guys, I am a newb around here. Just bought my first Jeep a couple of months ago. It is a 2012 Sahara, 4D, lifted (I think 2.5") with 35" Mud Grapplers and auto transmission. I drive ALL pavement. The other day, I was playing around with the instrument panel and saw that it auto calculates MPG. I was astonished to see is was at 9.6MPG. I reset it and ran through a tank of gas to find I was at 10.4. The next tank of gas got 11.1. I've done this a handful of times and been between 10-12 MPG. I certainly was not buying this toy for the mileage, and I knew the lift/tire combo would have some impact on MPG, but certainly had not expected this performance.

I read some previous posts about gear ratio making a big difference in mileage. I do not know what gear ratio I have as jeep's website does not have the window sticker for mine.

Is this likely a gear issue? If so, what options do I have to improve some gas mileage.

Thanks in advance.
Jake
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Old 03-12-2014, 03:37 PM   #2
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Jake. Did you flash the computer for your 35's. If not your computer still thinks you have stock size tires on. Also your shifting schedule will be off on your auto trans. Most likely you need an AEV ProCal or something like it to reset the computer.

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Old 03-12-2014, 03:42 PM   #3
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Originally Posted by Gunner View Post
Jake. Did you flash the computer for your 35's. If not your computer still thinks you have stock size tires on. Also your shifting schedule will be off on your auto trans. Most likely you need an AEV ProCal or something like it to reset the computer.
X2 on this get a superhips Flashcal or aev procal and it should fix that reading as well as your shift points. If you want to know what gearing you have crawl under and look up at the rear axle there should be a sticker on it (maybe still intact) and the ratio is usually printed as the last set of numbers.
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Old 03-13-2014, 08:26 AM   #4
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Gear ratio will make a difference as well. Download your build sheet and see what you have. As well as above posts.
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Old 03-13-2014, 09:23 AM   #5
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Your right foot is kickin your a$$

Oh, and what they said^^^
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Old 03-13-2014, 02:07 PM   #6
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Wink

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Originally Posted by Gunner View Post
Jake. Did you flash the computer for your 35's. If not your computer still thinks you have stock size tires on. Also your shifting schedule will be off on your auto trans. Most likely you need an AEV ProCal or something like it to reset the computer.
I am not a car person - sorry for my lack of knowledge. Last night I asked my girlfriend to pull up her top while we were cruising down the road. My mileage didn't change? I am not sure what it means to flash the computer.
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Old 03-13-2014, 02:12 PM   #7
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I'm in the same boat
Can't pull build sheet, getting 10mpg and bought it used so I have no idea what has been done to it

Flash the computer means basically telling the jeep it's got them big ol wheels on it
It will make your speedo off and some other things off as well
I doubt this has been done to mine but it's hard to tell
One thread I read on here said your jeep dealer might be able to program your computer for the wheels but im not sure how accurate this info is as I haven't gone into one yet
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Old 03-13-2014, 02:57 PM   #8
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If you google superchips flahscal or aev procal (those are exact names) you will find they are really easy to use and are just a plug and play unit. You measure your tires with measuring tape from top to bottom with the jeep on the ground. Round up to the nearest quarter of an inch. Then you input that value into the programer via how the instructions tell you. The programmer does the rest.
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Old 03-13-2014, 03:03 PM   #9
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Originally Posted by cdfreeTJ03 View Post
If you google superchips flahscal or aev procal (those are exact names) you will find they are really easy to use and are just a plug and play unit. You measure your tires with measuring tape from top to bottom with the jeep on the ground. Round up to the nearest quarter of an inch. Then you input that value into the programer via how the instructions tell you. The programmer does the rest.
Nice! Thank you. I will purchase one of these....looks like they are fairly reasonable. Will this have an impact on actual gas mileage (due to the transmission shifting) or will it just correct my computers incorrect calculation?
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Old 03-13-2014, 03:56 PM   #10
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Originally Posted by Tanner1828 View Post
I am not a car person - sorry for my lack of knowledge. Last night I asked my girlfriend to pull up her top while we were cruising down the road. My mileage didn't change? I am not sure what it means to flash the computer.
Pics or it didn't happen.
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Old 03-13-2014, 09:14 PM   #11
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Originally Posted by Tanner1828 View Post
Nice! Thank you. I will purchase one of these....looks like they are fairly reasonable. Will this have an impact on actual gas mileage (due to the transmission shifting) or will it just correct my computers incorrect calculation?
It will do both. Shift points being off are not conducive to ideal performance. And odometer being off will not give accurate MPG calculations. I drove my auto JK with 35"s for about 3 months before I got a procal, it made a big difference.

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