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  #25  
Old 12-25-2010, 11:37 PM
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Re: gas mileage? 4.0 what can i do?

Ok. On my 04' WJ 4.0L I got around 18MPG+ driving highway Full Time 4X4 Quadra Trac II. Have you changed your spark plugs? Are you filling it up with 87 Oct? Changed your Air Filter? What kind of Oil do you use in it? How often do you change the oil?

ANy Codes pop up? Maybe O2 Sensors?
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  #26  
Old 12-27-2010, 03:46 PM
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Re: gas mileage? 4.0 what can i do?

As stated a bunch of times, I would check and focus on the basics...like air intake, exhaust (cats maybe fouled, or 02's failing) plugs, etc. Beyond that, it's not that crazy to see 14-15 out of the 4.0. Lots will tell you they do better...and there are lots that do worse. I had a 4.0L Wrangler and XJ...both got the same. 15-17 city and highway, doesn't matter. Jeeps are not good on gas. That's not so bad when a 98 XJ purrs like a kitten, while most 98era Explorers I see are in the junkyards with the rear ends ripped out of them.

Open up the exhaust, open up the intake...get some good OEM sized tires and keep them inflated right, change all fluids and that's about the best you'll do with a moderatley heavy foot (like me).
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  #27  
Old 12-28-2010, 05:15 PM
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Re: gas mileage? 4.0 what can i do?

Quote:
Originally Posted by TJXJWJ View Post
As stated a bunch of times, I would check and focus on the basics...like air intake, exhaust (cats maybe fouled, or 02's failing) plugs, etc. Beyond that, it's not that crazy to see 14-15 out of the 4.0. Lots will tell you they do better...and there are lots that do worse. I had a 4.0L Wrangler and XJ...both got the same. 15-17 city and highway, doesn't matter. Jeeps are not good on gas. That's not so bad when a 98 XJ purrs like a kitten, while most 98era Explorers I see are in the junkyards with the rear ends ripped out of them.

Open up the exhaust, open up the intake...get some good OEM sized tires and keep them inflated right, change all fluids and that's about the best you'll do with a moderatley heavy foot (like me).
AMEN to that..best advice i've seen on the thread so far. My 2001 WJ with 123,00 runs 18-20 HWY and 14-16 in town..mileage could be subjective to any number of those things
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  #28  
Old 12-28-2010, 05:46 PM
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Re: gas mileage? 4.0 what can i do?

Check the fuel pressure at the rail and clean the fuel injectors.
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  #29  
Old 12-28-2010, 07:25 PM
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Re: gas mileage? 4.0 what can i do?

My dad's 4.0 WJ with 178k miles consistently got 20-21 mpg on interstate trips. My XJ with 5.5'' lift and 32's and 3.55's consistently gets 18-21 mpg out on the road depending on how and what speed I drive. Both of our jeeps do the best right around 65mph. I would just completely go through the jeep. plugs, O2's, fuel filter, etc. Maybe seafoam the jeep and run some injector cleaner through it for a few tanks. It should be getting much better mileage out on the road. Also, if you're going by what the overhead console says, I would suggest calculating it manually. Fill the jeep up, record the miles you drive, fill the jeep up again at the same station, and divide miles driven by the gallons you put back in. Its possible that the readout isn't correct.
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  #30  
Old 12-29-2010, 09:59 AM
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Re: gas mileage? 4.0 what can i do?

I tend to question people's methods of calculation too...everyone posts up their MPG's but where/how are they getting that number? The Jeep's computer is not a trustworthy source. Doing some quick math intermittently is not a trustworthy source either. Call me crazy, but since I don't do THAT much driving, it's not a big deal for me to track it closely. I have a spreadsheet and I enter exact mileage at fill up and always fill the tank completely. The spreasheet does the calculation and shows a running average. Consistency is the only way to get an accurate MPG number.
For example, I've entered EVERY fill up since I bought my 4.7 WJ back in June. My average is 15.5mpg. It spikes when I change the oil...usually to about 17 for one tank. A lot of people probably do much better, but my drive is about 10 minutes, all city everyday. There's a lot to be said for good fuel too...I'm not about to put GetGo, or go to some gas station I've never heard of. Steady diet of Shell and Sunoco for me.
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  #31  
Old 12-29-2010, 11:11 AM
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Re: gas mileage? 4.0 what can i do?

Quote:
Originally Posted by TJXJWJ View Post
I tend to question people's methods of calculation too...everyone posts up their MPG's but where/how are they getting that number? The Jeep's computer is not a trustworthy source. Doing some quick math intermittently is not a trustworthy source either. Call me crazy, but since I don't do THAT much driving, it's not a big deal for me to track it closely. I have a spreadsheet and I enter exact mileage at fill up and always fill the tank completely. The spreasheet does the calculation and shows a running average. Consistency is the only way to get an accurate MPG number.
For example, I've entered EVERY fill up since I bought my 4.7 WJ back in June. My average is 15.5mpg. It spikes when I change the oil...usually to about 17 for one tank. A lot of people probably do much better, but my drive is about 10 minutes, all city everyday. There's a lot to be said for good fuel too...I'm not about to put GetGo, or go to some gas station I've never heard of. Steady diet of Shell and Sunoco for me.
I have mine tracked on my phone. Obviously there's going to be some error in every calculation. You'll never get the exact same amount of gas into the tank before the pump kicks off. There's error in the amount from each pump (ie, pump may say you got 11 gallons when you actually got 10.8 gallons).

But my "ritual" is pretty established. During weeks where I drive to work I stop at the same Marathon and fill up on Sunday night, Wednesday after work, and Saturday evening/night. I always let it go until completely full and it kicks off for the first time. I then let it sit for a second so all the bubbles in the gas come out the fill neck. Then I turn the pump on slowly and let it go until it kicks off again. I then enter the numbers on my phone and it tracks mileage and tells if it was a week when I drove to work or when I didn't and my driving was city.

The computer in my Jeep has ALWAYS been within a couple tenths of what I calculate.
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  #32  
Old 12-29-2010, 08:05 PM
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Re: gas mileage? 4.0 what can i do?

This is sort of just me jumping in, but I'm pretty sure that in the manual for the WJs, it says only to use 87 fuel because that is what these are built for. Just thought I'd throw that out there.
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  #33  
Old 01-11-2011, 05:43 AM
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Re: gas mileage? 4.0 what can i do?

I went and ordered an OEM fuel filter last night from Kolak, I am due for an oil change in 500 miles or so, prolly some point next week, I'll have my mechanic change it out, and see what that'll do
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  #34  
Old 01-11-2011, 07:01 AM
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Re: gas mileage? 4.0 what can i do?

The computer is pretty much dead on. Problem is it shows you the milage you're getting at that moment.
If you are go down hill at 65 and not hitting the gas it shows a nice high mpg. In the same way if you take off up hill and hit the gas you can watch the MPG's go down.
Only way to get an average is to do what everyone is saying. Top off the tank drive refill and divide miles drive by gallons of gas. Best way is to do a two tank average.
I noticed with mine I get better MPG's if I look at the computer as I drive. (I tend not to be as heavy on the right peddle)
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Old 01-11-2011, 09:50 AM
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Re: gas mileage? 4.0 what can i do?

Quote:
Originally Posted by WJDave View Post
The computer is pretty much dead on. Problem is it shows you the milage you're getting at that moment.
If you are go down hill at 65 and not hitting the gas it shows a nice high mpg. In the same way if you take off up hill and hit the gas you can watch the MPG's go down.
Only way to get an average is to do what everyone is saying. Top off the tank drive refill and divide miles drive by gallons of gas. Best way is to do a two tank average.
I noticed with mine I get better MPG's if I look at the computer as I drive. (I tend not to be as heavy on the right peddle)
It depends on the WJ you're driving. Mine (2003 Laredo, I6, almost no options) ONLY tells you average gas mileage. My buddies Jeep (2001 Laredo, I6, EVERY option for that model) will tell him either instant gas mileage OR average gas mileage. Mine doesn't have the instant gas mileage.

But I have found that mine is pretty accurate to what I calculate. You do have to reset the computer and trip when you fill up to get the computer to have an accurate reading w/ the tank.
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Old 01-18-2011, 12:05 AM
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Re: gas mileage? 4.0 what can i do?

speaking of seafoam...do you pour into directly into the gas tank or what??
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