Not another MPG thread - JeepForum.com
 
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post #1 of 9 Old 11-16-2016, 05:28 PM Thread Starter
Airborne Lee
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Not another MPG thread

I don't want to start another MPG argument but there is something fishy about hitting 5k miles and having the MPG drop through the floor.

Recently bought my second Jeep Wrangler 4dr JK. Both with Penstar engines, auto trans, 3.73 gears stock wheels/tires.

My 2013 bought new got 17-20mpg average mixed highway and city driving until 5k miles, then it instantly dropped sharply to 12-15mpg. Everything stayed the same but miles on the odometer.

Dealership service manager said use only premium unleaded gas, no ethanol. I switch and mileage never went above 17mpg highway only. there was nothing else to do or wrong.

Now I have just purchased a new 2016 JK exactly the same thing just newer. Last month I drove over 5k miles again and my mileage did the exact same thing - instantly plunging to 12-15mpg. Only this time I have never used anything but premium unleaded with NO ethanol at all.

What gives, there is something in the programming that causes this and I want it fixed. Is there a reset in the ECM or TCM?


'16 JKU Rubicon, Tan, RR Front Bumper, 9500i, Atlas Rear w/Tire Carrier M416 Trailer
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post #2 of 9 Old 11-16-2016, 06:00 PM
pentastarguy
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hasnt happened to my 2 door. only ethanol in the tristate area.
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post #3 of 9 Old 11-16-2016, 06:18 PM
cranbiz
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How are you checking MPG? By the EVIC or calculating mileage divided by gas used?

The EVIC is not an accurate test of MPG.

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post #4 of 9 Old 11-16-2016, 07:00 PM
Kev M
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Something is wrong, but it could be you.

Here in the Northeast, and ethanol land, I see small seasonal swings in mpg with colder temps (denser air means more power but more fuel used) and winter formula oxygenated fuels that pack fewer hydrocarbons per gallon.

That said, even I don't dip below 18 mpg (JKU, 3.73, 6-spd, Non-highway).

Of course if your usage is true city, constant stop and go, lots of traffic lights, and short runs, then your mileage could be normal.

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post #5 of 9 Old 11-17-2016, 07:43 AM Thread Starter
Airborne Lee
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YEP, good thoughts, could be mixture of fuel, could be weather. Except it is not either.

Both Jeeps bought in January - both jeeps hit 5k in similar fall weather. This is not an additive, fuel mixture issue. Fuel mixtures are not going to make a drop in MPG of over 5 mpg overnight. And if mixtures did make that change it would have gotten better in spring and dropped again the following fall in my 2013. That never happened.

MPG checked both by dash and by calculation of gallons put in and miles driven. My calculations are correct.

This is clearly a change in the computers or engine itself.

Can the computers be reset to work as before?

'16 JKU Rubicon, Tan, RR Front Bumper, 9500i, Atlas Rear w/Tire Carrier M416 Trailer
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post #6 of 9 Old 11-17-2016, 08:02 AM
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Pull the Negative battery cable for 10 min to reset the computer. This may help. There could be a failsafe built in for 5k break in period, but then you should notice more power at the same time.

^^Jeff^^
2008 Black and Khaki Sahara Unlimited Trax-Lok rear diff. 3.5" Rock Krawler fr springs, rear TeraFlex 2.5 BB, D44HD/J8 w/ OX locker and RCVs, 37x12.50x17 Pitbull Rockers on ProComp 2635 Predator Alloys, AEV Prem Bumper, Smitty X2O 12K ETC..
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post #7 of 9 Old 11-17-2016, 08:07 AM
Kev M
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You seem to have it covered from a variables standpoint, but I'll ask just to be sure. There are no changes in usage then? More shorter trips, more traffic, etc?

If not, yeah, something I'd amiss.

There was no break-in calibration change that I noticed this past year. I just hit 10k miles on the JKU I picked up almost exactly a year ago. Like I said my mileage has been great (18-22, though the latter of the range only on true highway or long trips with few stops).

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post #8 of 9 Old 11-17-2016, 12:41 PM Thread Starter
Airborne Lee
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Quote:
Originally Posted by JTPhoto View Post
Pull the meg cable for 10 min to reset the computer. This may help. There could be a failsafe built in for 5k break in period, but then you should notice more power at the same time.
I've never done this can you help me identify the correct cable. Honestly, it does seem like it determined driving habits and adjusted. I remember something about the variable timing that "learns" driving habits. I can't help but thing there is something like this going on.

I have not seen any change in power good or bad. I have absolutely NOT changed any driving habits. I'm suddenly just sucking the tank dry.

'16 JKU Rubicon, Tan, RR Front Bumper, 9500i, Atlas Rear w/Tire Carrier M416 Trailer
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post #9 of 9 Old 11-17-2016, 12:55 PM
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Quote:
Originally Posted by Airborne Lee
I've never done this can you help me identify the correct cable. Honestly, it does seem like it determined driving habits and adjusted. I remember something about the variable timing that "learns" driving habits. I can't help but thing there is something like this going on. I have not seen any change in power good or bad. I have absolutely NOT changed any driving habits. I'm suddenly just sucking the tank dry.
Just realized my typo. It should have been Neg cable or Negative battery cable. And yes the computer is adaptive both in shift patterns and drivability

^^Jeff^^
2008 Black and Khaki Sahara Unlimited Trax-Lok rear diff. 3.5" Rock Krawler fr springs, rear TeraFlex 2.5 BB, D44HD/J8 w/ OX locker and RCVs, 37x12.50x17 Pitbull Rockers on ProComp 2635 Predator Alloys, AEV Prem Bumper, Smitty X2O 12K ETC..
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