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Unread 12-19-2013, 01:55 PM   #1
Yendor
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Fooled by the MPG-ometer

WTH, the first couple of tanks full, it was really close. This last tank, it said 18.4, and was really 16.8.

Not really that big of a deal, but if they went to the trouble of putting it in, and I paid for it, I want it to be more accurate than that.

Winter blend gas, perhaps?
Is this one of the things that can be re calibrated with a tuner?

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Unread 12-19-2013, 05:17 PM   #2
4x4jkx
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Mine has never been dead on accurate. Without knowing how Chrysler computes mpg on their vehicles I can't say as to why. General guess would be compounding errors in sensor readings.

I'm typically of by anywhere from .5 to 1.5 mpg
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Unread 12-19-2013, 05:24 PM   #3
krawler510
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More stop and go? More hills?
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Unread 12-19-2013, 05:42 PM   #4
442Wrangler
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Quote:
Originally Posted by Yendor View Post
WTH, the first couple of tanks full, it was really close. This last tank, it said 18.4, and was really 16.8.

Not really that big of a deal, but if they went to the trouble of putting it in, and I paid for it, I want it to be more accurate than that.

Winter blend gas, perhaps?
Is this one of the things that can be re calibrated with a tuner?
My 08 has never worked right either. Always been .5-1.0 off. Just a retarded set up IMHO
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Unread 12-19-2013, 05:49 PM   #5
Dead-On
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Chrysler's MPG calculator just sucks. If I reset it while accelerating or going up hill it reports a low number till I reset it again. If I reset it while going downhill or coasting it will give me a high number till I reset it. And some times it acts just whacky.
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Unread 12-19-2013, 05:51 PM   #6
ronjenx
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Quote:
Originally Posted by 442Wrangler View Post
My 08 has never worked right either. Always been .5-1.0 off. Just a retarded set up IMHO
That's about how much mine has been off, too.

On systems that can be tweaked, it takes a while to get it to be accurate.
The JK system can't be tweaked. I suppose one could play with the tire diameter, but then the speedometer/odometer would suffer.
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Unread 12-19-2013, 06:35 PM   #7
HAFICON
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I reset mine almost every day and it stays close, but I don't really care what is says I am going to drive my Jeep regardless..
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Unread 12-19-2013, 08:03 PM   #8
Tragyn
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Quote:
Originally Posted by Dead-On View Post
Chrysler's MPG calculator just sucks. If I reset it while accelerating or going up hill it reports a low number till I reset it again. If I reset it while going downhill or coasting it will give me a high number till I reset it. And some times it acts just whacky.
Um, what's it supposed to do? You're taking an average of fuel consumed over distance traveled. If you're going down hill, you'll cover more distance while using less fuel. Of course it'll report a high MPG...
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Unread 12-19-2013, 08:29 PM   #9
Dead-On
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Quote:
Originally Posted by Tragyn View Post
Um, what's it supposed to do? You're taking an average of fuel consumed over distance traveled. If you're going down hill, you'll cover more distance while using less fuel. Of course it'll report a high MPG...
I fully understand that but the calculations are affected by when I press the reset button. I have to be on relatively flat ground and accelerating at an average speed for it to be relatively correct. If I decide to hit the reset button and let off the gas for just 5 seconds to hit it the average will read high even if my trip is hundreds of miles. It seems to be worse if I hit the accelerator. If I am accelerating when I hit it (even for a few seconds) the average will read about 2-3 MPG lower than the actual usage even if I'm driving hundreds of miles. There's something up with the initial calculation process when you hit the reset button on my JKU .
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Unread 12-19-2013, 08:38 PM   #10
Tragyn
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Quote:
Originally Posted by Dead-On View Post
I fully understand that but the calculations are affected by when I press the reset button. I have to be on relatively flat ground and accelerating at an average speed for it to be relatively correct. If I decide to hit the reset button and let off the gas for just 5 seconds to hit it the average will read high even if my trip is hundreds of miles. It seems to be worse if I hit the accelerator. If I am accelerating when I hit it (even for a few seconds) the average will read about 2-3 MPG lower than the actual usage even if I'm driving hundreds of miles. There's something up with the initial calculation process when you hit the reset button on my JKU .
Ah, maybe you're right. I never paid particular attention. Usually I'll wait until I'm at cruising speed before resetting.
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Unread 12-19-2013, 08:43 PM   #11
JTPhoto
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The documentation specifies that the system records a value averaged over the past 500 miles if you don't reset it. If I reset mine at every fill up it seems to be pretty accurate. In order for it to be accurate the speedo/odometer must be accurate as well.
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Unread 12-19-2013, 08:50 PM   #12
Neo1130
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Mine is always within .2. I will fill the tank and reset the meter...
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Unread 12-19-2013, 11:30 PM   #13
SubAtomicGenius
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Could be temperature changes, cold weather, blended fuel, etc. Accuracy is also highly dependent on the driver's driving habits.
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Unread 12-19-2013, 11:34 PM   #14
ronjenx
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Quote:
Originally Posted by SubAtomicGenius View Post
Could be temperature changes, cold weather, blended fuel, etc. Accuracy is also highly dependent on the driver's driving habits.
Another thing that affects the accuracy is the fact that it doesn't directly measure fuel flow.
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Unread 12-19-2013, 11:40 PM   #15
SubAtomicGenius
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Yeah, I can sit outside the store idling (OMG! ) while waiting for the woman and watch the MPG go down... down... down...
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