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  #1  
Old 11-21-2011, 07:36 PM
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Gas Mileage dropping

I recently bought a 2004 Overland. (11-10-11 purchase date)
When I bought it, it had 74162 miles on it.
The overhead console indicated that average miles/gallon was 18.0.
The mileage has been dropping rapidly over the last couple weeks.
A little history...
Since day I purchased, I noticed the mileage drop by .1-.2 points.
Slight rough idle. Did a Seafoam treatment this past Sunday. LOTS and LOTS of smoke. Idle smoothed out a little.
Sunday I was at 17.5 miles/gallong.
Today, Monday, I am at 15.0mpg on overhead console.

My driving habits are normal. I drive the same route everyday. 80% highway, 20% smaller back country roads. Not much stop and go at all.

I have 74880 miles as of now. I am not sure what would be causing the mileage to drop so drastically so fast.

Is this normal for the 4.7? I was thinking more of the 18-20 for my driving style. I am not heavy on the foot.

Any insight would be helpful.
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Old 11-21-2011, 07:43 PM
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Re: Gas Mileage dropping

The EVIC is not always showing the exact values. Next time after filling up the tank, make a calculation yourself and compare it to the EVIC values.
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Old 11-21-2011, 07:53 PM
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Re: Gas Mileage dropping

ok, will do. What is the normal average with the 4.7 HO in real life?
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Old 11-21-2011, 08:27 PM
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Re: Gas Mileage dropping

Fuel filter replacement. Had the same issues with mine, and drastic mileage drop. Once the fuel filter was replaced, the mileage increased and ran MUCH better.
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Old 11-21-2011, 09:28 PM
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Re: Gas Mileage dropping

I have noticed that if I reset the EVIC at first start up it seems to be more accurate.
I always write milage and MPG on my reciept when I get gas and I find that the EVIC is pretty much right on.
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Old 11-21-2011, 09:30 PM
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Re: Gas Mileage dropping

Need a new filter with only 74k miles? is that normal?

Not sure if my rough idle is rough or just a "v8 rumble". I feel the motor shake while in park/neutral/sitting at stop light.
Should the running motor shake the Jeep? My 75CJ5 was rough, but all my other Jeeps have all bee 4.0L.

With such low miles, it shouldnt be ready for new plugs or filters yet. IMO.
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Old 11-21-2011, 11:38 PM
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Re: Gas Mileage dropping

I have 04' Overland and I can get 18mpg only if I drive on hwy with 60mph. On city driving, short distances I am at 12-13mpg with easy on the gas. I am asuming the previous owner did reset the overhead while driving on the hwy just before the sale (maybe on purpose) and now you are going back to the real numbers. Also the winter fuel does not help much for good mpg. Just wait a little before you start taking your Jeep a part.
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Old 11-22-2011, 12:21 AM
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Re: Gas Mileage dropping

Have you ever did a tune up on it? That might solve the rough idle and maybe even your gas issue.
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Old 11-22-2011, 06:19 AM
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Re: Gas Mileage dropping

Quote:
Originally Posted by PeterB16 View Post
Need a new filter with only 74k miles? is that normal?

Not sure if my rough idle is rough or just a "v8 rumble". I feel the motor shake while in park/neutral/sitting at stop light.
Should the running motor shake the Jeep? My 75CJ5 was rough, but all my other Jeeps have all bee 4.0L.

With such low miles, it shouldnt be ready for new plugs or filters yet. IMO.
Since you bought it used, there's no telling how it was driven, how it was maintained, etc. Don't let the mileage fool you on what may/may not be the problem.

I'd start with the smaller, less expensive things like the fuel filter, new spark plugs, etc.
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Old 11-22-2011, 07:01 AM
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Re: Gas Mileage dropping

Quote:
Originally Posted by tkdgirl View Post
Since you bought it used, there's no telling how it was driven, how it was maintained, etc. Don't let the mileage fool you on what may/may not be the problem.

I'd start with the smaller, less expensive things like the fuel filter, new spark plugs, etc.

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.
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Old 11-22-2011, 10:01 AM
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Re: Gas Mileage dropping

The fuel filter also has a pressure regulator build in. There is in fact no service interval for changing it, it just depends on if troubleshooting would tell you so. I also had an increased gasmileage after i had put some injector cleaner in the tank and at highway speeds i was missing power when trying to pass someone. Changing the filter/regulator solved both problems.
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Old 11-22-2011, 11:41 AM
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Re: Gas Mileage dropping

Quote:
Originally Posted by dsi jeep View Post
I have 04' Overland and I can get 18mpg only if I drive on hwy with 60mph. On city driving, short distances I am at 12-13mpg with easy on the gas. I am asuming the previous owner did reset the overhead while driving on the hwy just before the sale (maybe on purpose) and now you are going back to the real numbers. Also the winter fuel does not help much for good mpg. Just wait a little before you start taking your Jeep a part.
Good point. This morning while on the interstate, just cruising, I was getting between 18.5 and 20 mpg, until I hit the gas.

On the way to work this morning on the back roads I was getting 12-13. I guess the previous owner DID reset overhead. Sneaky bugger.
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