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Unread 07-19-2013, 09:49 AM   #1
dualtjs
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Avg MPG Calculator Error: Sign of Other Issues?

All of my searches have returned MPG discussions related to tire size, weight, etc, so I'll apologize if this has been discussed, but I can't find it (either via JF search or google search).

I got home from a trip to the coffee shop this morning and the Avg Eco reading was 18 mpg (not unusual, since I filled up, reset and almost all subsequent driving was highway). I got back in it a couple hrs later with the same reading and went to the store a couple miles away. When I got back in for the trip home, the Avg Eco mpg read 9.0.

I'm not naive enough to believe that these calculators are 100% accurate (in fact, the reading on my JK is usually 1-1.5 mpg lower than actual based on pump and odometer readings at fill up), but this isn't a calculator error. In this case, the system is simply not working correctly and appears to give random numbers when it wants to. Has anyone else experienced similar results? Is there a chance that this is an indication of other possible problems?

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Unread 07-19-2013, 09:56 AM   #2
SoCal_HEMIHead
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I find mine varies a lot after a reset. I believe this to be true since it's calculating the "average", so it doesn't take much to throw off the average. The longer I drive, the more it will balance out the highs and lows.
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Unread 07-19-2013, 10:55 AM   #3
222Doc
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THis^^^^^^^

if you are on a steep grade going down hill. Hit the reset on our 012 I can get that thing to read over 1000mpg. who says a Jeep aint like priuse
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Unread 07-19-2013, 10:55 AM   #4
dualtjs
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The problem in my scenario is that I drove almost 40 miles to get the 18 MPG when I arrived at home. The trip to the store was 2 miles. I would have to get less than 1/2 MPG, to get 9 MPG when I got back in for the drive home. No way this is real fluctuations in due to different driving conditions, early after reset.

Edit: upon recalculating, the MPG for the trip to the store would have to be negative, to go from 18 MPG at 40 miles, to 9 MPG at 42 miles.
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Unread 07-19-2013, 02:57 PM   #5
rha600
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You absolutely could be getting 1/2 mpg.

Like SoCal said, it varies A LOT when you first reset, and what it will do is that if you are say, at a traffic like, you are still burning fuel, but you're now getting 0 mpg. It factors that in. I've literally watched mine go from 24mpg down to 13mpg while waiting for one red light. Now this was within 1-2 miles of resetting it, but point being, if you did sit at a traffic like, or had the Jeep running while you ran in the store...that's what hosed you.
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Unread 07-19-2013, 03:49 PM   #6
JoonHoss
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probably just hit the reset while driving right before you got home

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Unread 07-19-2013, 07:03 PM   #7
dualtjs
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Quote:
Originally Posted by rha600 View Post
You absolutely could be getting 1/2 mpg.
I suppose if I let it idle for 15 min or more, that's possible. I wouldn't bring up the matter, if that were the case. We're talking about a 3-4 min trip to a store ~2 miles away, which means that the trip would have to have negative MPG to get the results.

The accidentally hitting reset is a logical suggestion. I don't think that I did (my system requires at least 1 full second press to reset), but anything is possible.
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Unread 07-19-2013, 10:21 PM   #8
ncb
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Don't lose sleep over it. It's not a very accurate gauge if you reset it and immediately check it. To be even close to accurate I've noticed you have to leave it alone and run a couple tanks through it. Checking mpg the old fashioned way is more accurate.
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Unread 07-20-2013, 09:58 AM   #9
rayder1
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I accidentally bump the reset switch from time to time. Maybe that happened.
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Unread 07-21-2013, 01:55 PM   #10
rha600
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Quote:
Originally Posted by dualtjs View Post
I suppose if I let it idle for 15 min or more, that's possible. I wouldn't bring up the matter, if that were the case. We're talking about a 3-4 min trip to a store ~2 miles away, which means that the trip would have to have negative MPG to get the results.

The accidentally hitting reset is a logical suggestion. I don't think that I did (my system requires at least 1 full second press to reset), but anything is possible.
The distance to the store doesn't matter. it's how long it took to get there.

Read the rest of my post, right after resetting mine, I lose 11mpg just sitting at one red light. I don't believe that would be accurate, but it did do it. So if you did just reset the mpg and went to the store, even it it were 1/3 mile away, if there were 2 red lights in between and maybe it took a while pulling out of your street, it will drop big time.

On a side note, my last jeep did not do this. Sure it would drop as I sat in place longer and longer, but this one drops FAST.

Oh, and it's never been as much as you experienced, but I have been at 18mpg when I get home, wake up the next morning, go to leave for work and it shows 15 or 16mpg. Dunno what's up with that.
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Unread 07-21-2013, 07:34 PM   #11
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Quote:
Originally Posted by rha600 View Post
The distance to the store doesn't matter. it's how long it took to get there.
Distance certainly does matter. Short distance taking a long time will cause the correct MPG to drop significantly. Sitting an idling in my driveway for 15 min can cause a large drop in MPG. I stated distance and time, to ensure that anyone reading it didn't hypothesize that I sat at idle for a lengthy time period.
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Unread 07-22-2013, 06:08 AM   #12
rha600
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Nevermind.

If you keep reading past the part where I lost 11mpg at ONE RED LIGHT then I can't get it through your head that 3-4 minutes is long if you just reset the system.
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Unread 07-22-2013, 06:38 AM   #13
murfysflaw
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Quote:
Originally Posted by rayder1 View Post
I accidentally bump the reset switch from time to time. Maybe that happened.
I'd bet this is your issue too. Happens to me quite often.
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Unread 07-22-2013, 09:03 AM   #14
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Quote:
Originally Posted by dualtjs View Post
Is there a chance that this is an indication of other possible problems?
Probably not.
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Unread 07-22-2013, 10:09 AM   #15
Wavedatya
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Talk about mpg. I drove 2000 miles and an average of 12 mpg. Now that sucks.
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