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Unread 01-12-2012, 12:43 PM   #1
neddevine
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1997 TJ Wrangler 
 
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Really Bad Gas Mileage!

G'day, new to jeeping, love it except the gas mileage is beyond ridiculous. I know and was expecting bad mpg on a 160,000 mile 1997 2.5L but 8 yes 8 mpg is just wrong. Tires are 30x9.5x15
I am going to change: front and back o2 sensors, injectors, coolant temp sensor, tune up etc. Compression test will also be taken.
There are no codes to review. No vacuum leaks.
Engine runs good, starts right up, has power with no missing.

I need real help please, no I won't sell it!

Any practical input truly appreciated.
Thanks in advance

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Unread 01-12-2012, 12:54 PM   #2
TheBoogieman
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I'd start with plugs,wires,distibutor cap.My 2.5L on 31's had 200,000 miles on it and always got around 15 mpg city.
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Unread 01-12-2012, 01:14 PM   #3
canyon
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It could be a small crack in exhaust header? Just throwing it out there.
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Unread 01-12-2012, 01:16 PM   #4
mdm
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O2 sensor?
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Unread 01-12-2012, 01:41 PM   #5
Dextreme
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You are talking highway/city mpg correct? Because I get about 8mpg gallon in 4 low.
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Unread 01-12-2012, 02:29 PM   #6
vtx531
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How are you calculating this?
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Unread 01-12-2012, 04:46 PM   #7
4banged
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Quote:
Originally Posted by Dextreme View Post
You are talking highway/city mpg correct? Because I get about 8mpg gallon in 4 low.
LMAO

Seriously though, I only get about 14mpg in mixed driving with my 03 2.4l 4 speed auto 31" tires. I've done the wires, plugs etc and have considered replacing the O2 sensors so let us know what you find to be the culprit.
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Unread 01-12-2012, 04:51 PM   #8
94yjstocklook
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8mpg definitely sucks. On my 94 4.0 6 cyl. i get roughly 13/15mpg. Sorry for no help but definitely something going on.
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Unread 01-12-2012, 05:26 PM   #9
Jim Shanks
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My last few fills with my 4.0 has netted around 7-8mpg. I'm looking into a diesel powerplant for the TJ.

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Unread 01-12-2012, 06:37 PM   #10
1999TJRED85000
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I think everyone hit the major things you can check. The first thing I thought was Oxygen sensor. If your sensors are off, the CPU will think things are happening that aren't and bad mileage is usually the immediate result. Plug wires and plugs might hurt a little, but it would have to be running really rough to get that poor of mileage. If you're a mechanical type, give it a full tune up with new wires, OEM plugs, dist. cap, air filter, oil and oil filter change, etc. In other words, do all the cheap stuff that should be done anyway. Oxygen sensors aren't that expensive either, but if you aren't familiar with how they work, take it to a local wrench.

Hope this helps.
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Unread 01-12-2012, 06:57 PM   #11
silver97tj
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Hi all lets be honest anything for a jeep tj in the range of 12 -14 mpg is good, anything over 17 is not reality. This is a jeep not a honda civic!.............just do tune up, and change O2 sensor and check cats. etc etc, most of this is do it yourself, pretty easy................
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Unread 01-12-2012, 07:04 PM   #12
biffgnar
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Quote:
Originally Posted by silver97tj View Post
Hi all lets be honest anything for a jeep tj in the range of 12 -14 mpg is good, anything over 17 is not reality. This is a jeep not a honda civic!.............just do tune up, and change O2 sensor and check cats. etc etc, most of this is do it yourself, pretty easy................
Being honest 14 is not good for me. 14 is a disappointing tank.
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Unread 01-12-2012, 07:26 PM   #13
Dorian772
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Quote:
Originally Posted by Dextreme View Post
You are talking highway/city mpg correct? Because I get about 8mpg gallon in 4 low.
that made me laugh
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Unread 01-12-2012, 07:52 PM   #14
catsknr
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Dont forget to check the thermostat, if stuck open it will run too cool and comp. will feed it rich to try to warm up.
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Unread 01-12-2012, 08:26 PM   #15
neddevine
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Thanks for all the input.
Filled tank then ran until quarter full then refilled 12 gallons and 97 miles.
Second tank half full 8 gallon 63 miles. Mix of city and hwy driving in 2 wd not 4 low! Thermostat works fine.
Thanks to all for input. I will, over next few days change parts, test and report back.
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