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Unread 02-26-2006, 04:00 AM   #1
RFisher
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Bad Tune Up

2000 Grand Cherokee 4.7 V8 with 66K miles.

I had major tune up on September 9th, with 59,809 miles at Dealer, and ever since tune up my gas mileage has decreased. It went from before tune up 24mpg highway, to after tune up 20mpg. I went in at 61,971 miles for oil change, and I complained, but they said there is nothing they can do about mpg. That tune up doesnt adjust anything, just changes plugs, air filter, fuel filter, and they clean it up.

The engine seems to run smoother at idle than before, but going up mountain pass it down shifts sooner than before tuneup. They did transmission service same time as tune up.

Now I have 66,120 miles, and am still getting 20.1 mpg at best highway.

Any suggestions?

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Unread 02-26-2006, 04:09 AM   #2
Briandl
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Those are pretty average numbers, EPA is something like 16/19 for the 4.7L V8. Threads here indicate most people get 19-21 on the highway, with some rare instances of 22-24 but only under specific circumstances, on specific trips, and not over the course of any length of time. For example "I drove to X City 300 miles away and got 24 miles per gallon".
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Last edited by Briandl; 02-26-2006 at 04:30 AM..
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Unread 02-26-2006, 05:02 AM   #3
RFisher
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replaced

They replaced; spark plugs, air filter, pcv, serpinetine belt, 4 tires, 2 front brakes, all 4shocks.

Fuel injector service, serviced throttle body, transaxle service, flushed power steering.

After spending all that money, i was hoping to have at least as good of gas mileage, not worst.

I asked about fuel filter, they said it is in gas tank, not replaceable.
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Unread 02-26-2006, 06:27 AM   #4
rwild
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I had a 99 w/ 4.7 and my service book shows a inlet screen type filter at the bottom of the fuel pump in the tank. It also shows a fuel filter/fuel pressure regulator mounted to the body just in front of the tank. Don't think this will help your MPGs but might in the future to know were it is.
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Unread 02-26-2006, 06:44 AM   #5
greasefingers
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For the most accurate results you calculate your mileage by filling up until the gas nozzle shuts itself off. Then divide miles traveled by gallons needed to refill. Do not use the computer or vehicle information center display.

Your oxygen sensor could have drifted a bit, but I doubt it as anything near 20 mpg is a blessing. I have never heard of anyone getting 24 mpg with any v8 engine.
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Unread 02-26-2006, 06:58 AM   #6
Woody
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One contributing factor you should look into is the type of fuel being used now. Most states require a different fuel for winter driving in comparison to the fuel used in the summer. It usually decreases the gas mileage of any vehicle 1-3 mpg.

You changed all that stuff hoping for better mpg, well if you really were getting 24 mpg using a calculator, and not the overhead display, you should've been counting your blessings already, because you are getting better mpg than anyone else on this board with a V8.

I'm betting the computer told you 24 when in reality it was closer to 20. Somehow the tuneup or maybe the disconnection of the battery or some other odd thing has reset the computer and now the mpg reading is closer to what it really is.


No I am not calling you a liar, I have once gotten 24 mpg on the highway, but that was with aluminum rims, fairly worn tires (weigh less than new ones) no roof basket, and I was driving 67 mph down the freeway. It is possible to get this type of mileage, but not typical. Since I tuned up, and got fresh tires, installed a roof basket, and got another 2" of lift, the mpg went to about 17 on the highway at the same speed. Even without the roof basket the best I could achieve was 18. Now I've thrown a manual tranny in as well and I get about 19-20 depending on my speed.

I highly doubt you'll ever get back to 24 mpg. Just out of curiousity, is your WJ a 4x4? Also, they didn't do a transaxle service, as you don't have one of those. You could have had a transmission service, and a seperate axle service, but that's not the same. Transaxles are used on the front wheel drive cars nowadays. Where the transmission routes power directly to the wheel using a CV jointed axle shaft.
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Unread 02-26-2006, 07:13 AM   #7
SteelBlue_WJ
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yuo should feel lucky, on my last run to Tucson I averaged city and highway of 11.5 for the 4 days I was there...
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Unread 02-26-2006, 07:47 AM   #8
Turbonut
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Quote:
Originally Posted by greasefingers
For the most accurate results you calculate your mileage by filling up until the gas nozzle shuts itself off. Then divide miles traveled by gallons needed to refill. Do not use the computer or vehicle information center display.

Your oxygen sensor could have drifted a bit, but I doubt it as anything near 20 mpg is a blessing. I have never heard of anyone getting 24 mpg with any v8 engine.
Calculate the mileage over a couple of fillups as indicated. Personally, I think you'd be lucky to see 18/19MPG as an overall average, as the EPA mileage for the '99 4.7 V-8 is 15/19, and we all know it's difficult to see the upper number in everyday driving.
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Unread 02-26-2006, 08:46 AM   #9
SteelBlue_WJ
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Quote:
Originally Posted by Turbonut
Calculate the mileage over a couple of fillups as indicated. Personally, I think you'd be lucky to see 18/19MPG as an overall average, as the EPA mileage for the '99 4.7 V-8 is 15/19, and we all know it's difficult to see the upper number in everyday driving.
i was getting 20 avg pre lift/tires/roof basket...
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Unread 02-26-2006, 09:04 AM   #10
Turbonut
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Quote:
Originally Posted by SteelBlue_WJ
i was getting 20 avg pre lift/tires/roof basket...
I certainly hope you know how to calculate MPG. That's fantastic-Even better than my 4.0 XJ I had. I must be doing something wrong as my '01 Laredo 4.7, only sees 17.2 MPG average, and that's with a great deal of highway driving.

I just don't get it. How can people average more than the EPA best?????
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Unread 02-26-2006, 09:25 AM   #11
SteelBlue_WJ
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Quote:
Originally Posted by Turbonut
I certainly hope you know how to calculate MPG. That's fantastic-Even better than my 4.0 XJ I had. I must be doing something wrong as my '01 Laredo 4.7, only sees 17.2 MPG average, and that's with a great deal of highway driving.

I just don't get it. How can people average more than the EPA best?????
I tend to drive like I have an egg taped on my gas pedel and back then i did alot if hiway.
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Unread 02-26-2006, 09:51 AM   #12
greasefingers
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If I could average 24 mpg every week I would own three SUVs instead of two.
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88 Cherokee 2-door with 5speed manual 139K miles(deceased) purchased new
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Unread 02-26-2006, 01:36 PM   #13
Briandl
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Quote:
Originally Posted by Turbonut
I certainly hope you know how to calculate MPG. That's fantastic-Even better than my 4.0 XJ I had. I must be doing something wrong as my '01 Laredo 4.7, only sees 17.2 MPG average, and that's with a great deal of highway driving.

I just don't get it. How can people average more than the EPA best?????
I agree, I don't care what the circumstances are, it's difficult to average higher than the EPA Highway estimate....
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Unread 02-26-2006, 07:47 PM   #14
RFisher
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24 mpg

Yes i did calculation correctly, math is my strong point. The math results always matched the computer also. 23-24mpg every week since I bought this vehicle in 2000. It has towing package, not 4x4.
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Unread 02-26-2006, 11:19 PM   #15
Woody
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In that case, I vote the winter gas with the crap additives, or a little extra idling or something along those lines.
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