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  #13  
Old 11-22-2011, 11:42 AM
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Re: Gas Mileage dropping

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Originally Posted by JWeidner View Post
Agree, assuming you dont have the records I would just go ahead and do the 60,000 mile service. Diffs, transfer case, plugs, oil, PCV, etc.
No service records. I will do 60k mile service.

Thanks for reply's guys. Very helpful.
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Old 11-22-2011, 11:59 AM
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Re: Gas Mileage dropping

I get 15 out of my HO in PREDOMINANTLY city and suburb driving. They are thirsty. I'd start with the basics though.
Make sure you're up on all service, tire pressure, air filter is clean, plugs, clean throttle body, etc. If after that you see no improvement, I would think it's just that the previous owner drove like a little old lady. You can also experiment with fuel. The HO (at least mine) seems happier on the high test fuel.
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  #15  
Old 12-05-2011, 04:44 PM
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Re: Gas Mileage dropping

Do you know what gear ratio you have. My 04 Overland has 3:73 gears. I think that came with the trailer package. If your Overland does not have a trailer package, yuo may have something like 3:50 gears. My average is 18.8 right now. If i reste the readout while driving on the Interstate, I get 20 or better even at 70 MPH. Tire size may make a difference too. Do you have stock size tires? In the past, I have seen the milage drop as the miles increase. I guess from internal wear and the lose of compression. You don't have that may miles, but then again when you buy used, you really don't know the habits of the previous owner.

You got a lot of good responses and ideas. Good Luck
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  #16  
Old 12-05-2011, 04:57 PM
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Re: Gas Mileage dropping

Also make sure you are at a dead stop when you reset your EVIC. One time while I was cruising on the hiway at 65 mph I accidentally hit the reset button and was amazed at the display. It read 54.3 mpg. Maybe I should have quickly sold my WJ. lol
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  #17  
Old 12-05-2011, 05:07 PM
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Re: Gas Mileage dropping

Yes MeFix, very good responses.
I do have the trailer package, stock tires and 3:73 gears.
I am thinking the Jeep just wasnt maintained as it should have. I took the IAC valve off and it was nasty. I am betting there is tons of carbon built up.
I am going to do all the small stuff. I have already changed plugs. Next is fuel filter and fluid changes and cooling system back flush.
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  #18  
Old 12-05-2011, 06:20 PM
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Re: Gas Mileage dropping

The carbon build up is something we used to see when we had lead in the gas. Today, I'm not so sure we have carbon build up. Any build up might come from blow by which can make the intake channels look pretty oil covered and black. Then maybe some dirt that gets past the air filter. From my experience, if you pull the plugs and they look clean, I'd say you are running a good fuel mix.

My first Jeep Grand was a 1996 model with the Inline 6. I had an issue with the o2 sensors. When the engine heats up, the system should go into what I think they call lockup, which means the o2 sensors are telling the ECM how to feed fuel in. If either the upstream or downstream sensor is bad, the system will never go into lockup and you will suffer with poor fuel milage. That problem usually comes with an error code and or check engine soon light, which I had. If you do not have any error codes set, you most likely do not have that issue. I think that code I had was P0402. I'm sure there are other issues that might cause your milage to drop off , but that is my experience. The V8 runs great and would most likely pull just about anything I wanted to tow. It's just not a ride for great milage.
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Old 12-05-2011, 08:17 PM
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Re: Gas Mileage dropping

Ironically, just P. Coded for a new TPS, replaced it, and now my MPG has gone from 17.1 to 15.6. O2 sensors?
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Old 12-06-2011, 01:14 AM
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Re: Gas Mileage dropping

Check the fuel filter and the fuel pump, may need replaced. And try cleaning out your fuel system and add engine restore to the oil. It all helps it run better and helps clean and prolong engine life.
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