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Discussion Starter · #1 ·
Ok so I check my gas mileage every time I fill the jeep up and get about 15mpg
(3.07 gears 31" tires 2" lift 19 gal tank stock speedometer gear as far as I know) now all of a sudden the past 4 times I have filled it up I have been getting about 11.5mpg. I thought it was my driving the first time I filled it up. but after that i started to noticed that I wasnt getting the same miles per tank as I usually do ( the first quarter tank I get about 50-70miles and the rest are 50miles so about 210per tank). Is it the freakin winter gas already? I didn't notice that big of a drop last winter, the only time I got down to 11mpg was when I had to use 4wd last winter. I don't think it is the spark plugs yet I replaced them less than a year ago maybe 10,000 miles ago. What else could be causing this? Oh I should add that I have not noticed any loss in power.
 

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Discussion Starter · #3 ·
It's reformulated gas they use in winter. It has lighter component/ ingredients if you will. They use it to counteract what happens to your vehicle in the cold, it helps it start up easier and keeps emissions down in the winter. That is about all I know about it lmao
 

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To OP......when was the last time you did or had a basic tune-up? First thing I would do is check/ change air filter, and depending on your rig....if it has the coil rail the rest of a tune-up is swapping plugs and some little springs....could also check tire inflation with cooler temps.

Easily possible that it will take all of theses to get back to where you should be, if this doesn't "fix" it, my next GUESS would be one of the sensors is giving bad "juju" to the computer.

Good Luck!!!

Just saw 10,000 miles since plugs....I would still pull and check them..it is not out of the question for them to be bad already.
 

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Discussion Starter · #7 ·
To OP......when was the last time you did or had a basic tune-up? First thing I would do is check/ change air filter, and depending on your rig....if it has the coil rail the rest of a tune-up is swapping plugs and some little springs....could also check tire inflation with cooler temps.

Easily possible that it will take all of theses to get back to where you should be, if this doesn't "fix" it, my next GUESS would be one of the sensors is giving bad "juju" to the computer.

Good Luck!!!

Just saw 10,000 miles since plugs....I would still pull and check them..it is not out of the question for them to be bad already.
Yeah I'm going to check the plugs an everything else is good. Air filter gets changes every few oil changes so its still good too (just checked it to make sure it wasn't dirty.

Can anything else be causing this lack of gas mileage all of a sudden?
 

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If in your opinion everything else is good about has to be a sensor....UNLESS you have cap rotor and plug wire set-up...not telling you to throw money or just change for the CHANCE it might be the issue.....but when you have a computer controlling spark timing and fuel mix...old saying applies "garbage in garbage out"
 

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Discussion Starter · #9 ·
If in your opinion everything else is good about has to be a sensor....UNLESS you have cap rotor and plug wire set-up...not telling you to throw money or just change for the CHANCE it might be the issue.....but when you have a computer controlling spark timing and fuel mix...old saying applies "garbage in garbage out"
What sensor could it be?
 

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I am not kowledgeable enough to tell you which sensor, and been so long since I used an o scope couldn't even read it. Basicaly the sensors tell what is going on when and the computer "adjusts" to keep it in optimum "tune" for the type/ quality of gas air spark/ and timing, so if one of the sensors is off, or worse more than one, the tune coming from the computer would be incorrect which could make it run "rich" and burn ore fuel. If there are no "codes", than I am not gonna be much help....and even than I could only steer you to a place to find the "solution" for the code issues.

This Forum is usually pretty good for that...surprised there have not be more responses. Idle or one of the air sensors would be my first GUESS but I wouldn't rule out Cat issues either.
 

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Discussion Starter · #11 ·
I am not kowledgeable enough to tell you which sensor, and been so long since I used an o scope couldn't even read it. Basicaly the sensors tell what is going on when and the computer "adjusts" to keep it in optimum "tune" for the type/ quality of gas air spark/ and timing, so if one of the sensors is off, or worse more than one, the tune coming from the computer would be incorrect which could make it run "rich" and burn ore fuel. If there are no "codes", than I am not gonna be much help....and even than I could only steer you to a place to find the "solution" for the code issues.

This Forum is usually pretty good for that...surprised there have not be more responses. Idle or one of the air sensors would be my first GUESS but I wouldn't rule out Cat issues either.
Yeah I'm surprised more having chimed in lol bu we will see what happens. I don't think it is a cat issue normally you get a significant loss of power but I'm no expert lol.
 

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I would take it to your local auto parts store and have them run a scan for any stored codes. Codes can be stored even if your check engine light isn't on. It sounds like it may be an O2 sensor to me.
 

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Discussion Starter · #14 ·
Yeah planning on it. Just need the time. Thanks guys ill be postin back when I have it checked for codes
 

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Maybe partially caused by tire pressure. I know mine get a little low when the weather cools down.

EDIT: already suggested, nm
 

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My initial thought is one of your 02 sensors has gone bad and has caused your air/fuel mixture to go full-rich which reduces both power and economy. A bad 02 sensor won't necessarily trip the Check Engine light or generate any type of diagnostic code because it's difficult for the engine computer to always know, especially on older two 02 sensor equipped TJs, when an 02 sensor is generating bogus information.

On early TJs like my '97, the usual bad 02 sensor was its upstream 02 sensor which was the sole sensor responsible for the air/fuel mixture. Newer TJs have multiple 02 sensors and all have at least some say on the air/fuel mixture ratio.

No guarantee a bad 02 sensor is the cause but like spark plugs, 02 sensors do go bad and always eventually go bad and will need to be replaced. Sometimes catching a whiff of gasoline odor in the air in the passenger compartment can be a confirming symptom the air/fuel mixture is too rich.
 
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