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Discussion Starter #1
I just changed out my plugs with the OEM plugs that I bought from my Jeep dealer(NGK). They are the exact same plug that I took out.

I checked the gap on each plug, had to adjust one or two but for the most part they were perfect.

I just took a 700 mile round trip yesterday and only averaged 11.5 mpg highway. On this same trip which I do regularly I normally get 16-17mpg due to the hilly terrain. On flat road I use to get 18 easily.

I put my scanner on it and I'm not getting any codes. No CEL either

It runs great, plenty of power and acceleration and a smooth idle.

What the %@(( is going on?
 

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Discussion Starter #2
I went deeper into my scanner and checked "misfire" history. All 8 cylinders read the same number of fires and no miss fires stored in the history at all. A/F ratio was dead on perfect. All sensors and outputs were in the middle of the range.

Air pressure in the tires are all dead on 37psi. I ran 67mph for the whole trip.

My tires are new with less that 1k on them (Nitto Crossteks, stock size)

I'm at a loss. The Jeep has 27k on it and is in A-1 condition inside and out. I have always maintained it well since I bought it new.

On a side note, my climate control on the drivers side blows hot all the time no matter where I have the temp set at. Very annoying. Going to the dealer about that one. I think its either the thermostat, sensor or blend door.
 

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Try disconnecting the battery, turn the key on, wait 15 minutes, turn key off, reconnect battery, drive it around for a while and see what happens.
Hmm, Do you really think this will help the fuel mileage. I can see where it may help the climate control issue.

I'm about due my first battery so I might just kill two birds with one stone. I'll post back a report in a week or so after I get some everyday driving out of it.
 

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I can see how it would help the gas mileage but do you really think it will help the climate control issue? How?
 

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I can see how it would help the gas mileage but do you really think it will help the climate control issue? How?
Well, the issue with the climate control could be the computer that controls it. I have no way to monitor it.

However I can monitor the ECU inputs/outputs and I do not see any apparent issues.
 

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Try disconnecting the battery, turn the key on, wait 15 minutes, turn key off, reconnect battery, drive it around for a while and see what happens.
I'm having similar mileage issues. What is it about disconnecting the battery and draining capacitors that helps with the poor mileage?
 

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I'm having similar mileage issues. What is it about disconnecting the battery and draining capacitors that helps with the poor mileage?
It resets the computer, which will then relearn your driving habits.
 

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It resets the computer, which will then relearn your driving habits.
Oh, I didn't know that. I've bought about four tanks of fuel since I noticed my city mileage was down to around 11-12 mpg. I wish I'd asked sooner! Thanks for the tip. Cheers. Jorge
 

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Discussion Starter #11
I did this today, we will see how the mileage thing goes but my climate control is now working again LOL!
5 days later and a couple hundred miles and its still getting 11 in town and that is babying it. I'm wondering if they switched to winter gas about the same time I installed the new plugs?

I'm getting a slight "surge" or "pulse" on steady throttle and I have not felt the MDS/VVT kick in since the plug change. Still no codes, all of the output/input data looks normal.

I'm still at a loss.
 

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Discussion Starter #12
Just an update. I took the Jeep to the dealer for its last warranty trip before the 3/36 ran out. They said all was well with everything and no repairs were needed.

Today I ran the same trip that just 3 weeks ago I only got 11.5mpg on and I averaged 18.5 for the same trip! So whatever the dealer did that they did not do seems to have "fixed" the poor fuel economy issue:dunno:
 

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Huh, very interesting.
 
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