4.0 XJ fuel mileage improvement - any ideas?

Hi everyone.
I found this stock 1991 4.0 XJ Limited with an automatic transmission for a reasonable price but the owner says it gets 11.5-13 mpg city. What with fuel prices over here in europe being 2x-3x what they are in America, I won't buy it unless I can improve the mileage significantly (17-19 mpg or more city average, preferably).

So I did some research & found this article: http://www.4wheeloffroad.com/brandpages/jeep/131_0403_jeep_xj_cherokee_mileage/index.html
Maybe some of you have seen the article before and I was wondering what your experience with these kinds of mods are. I thought I'd check with you guys who have experience with this car before investing in one.

So basically, do the following mods do any good for the gas mileage & how much of an increase should I expect for a 4.0 XJ that gets 11.5-13 mpg? :

Bored-out throttle body
Throttle-body spacer
Air intake and filter
MAP (manifold absolute pressure) adjuster
Turbo City bolt-on exhaust
Performance Distributors Firepower Ignition kit

Here's links to the stores mentioned in the article...
http://www.turbocity.com
http://www.4wd.com/


Also I know to keep the tire pressure right, make the car a bit lighter & drive conservatively.

So can you guys recommend anything else to get better fuel mileage?

Thanks for the help, in advance.

I have never heard of an XJ getting that bad of mileage there has to be something wrong mechanically. You just may be running too Lean I wonder if the O2 sensors are still good on it. You should be running 17-21 MPG at all times. I would do a good air intake cleaning. Run some seafoam through the throttle body. (if they sell that there). Well this is not Your XJ I would just shop around some more. I dont know how Rare XJ's are in Iceland but there has got to be one that gets a lil better mileage.

My 01 runs about 12 city with new plugs, o2 sensors. I have heard several others also state that about 13 is the best they get for city driving. New it is listed as 16 MPG City so that is best case. I am sure you can get a few more MPG out of it but I would not count on it.

BlackCat01 said:

My 01 runs about 12 city with new plugs, o2 sensors. I have heard several others also state that about 13 is the best they get for city driving. New it is listed as 16 MPG City so that is best case. I am sure you can get a few more MPG out of it but I would not count on it.

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Really hmmm maybe it is cause mine is Renix but i get right at 18 MPG city... Your XJ gets as good a MPG as my Commander.

When I bought my XJ I was getting 18mpg average. Then I bought a gas from a Speedway gas station and it dropped to 14mpg. By the way, everything is stock. Since then I changed o2 sensor (both), plugs, cap, rotor button, and wires. Only got up to 16mpg. My dad suggested changing the fuel filter since Speedway's gas is junk, now I'm back to 18mpg. Hope this helps. Oh yeah, I no longer buy Speedway gas.

Thanks for the replies. I really appreciate it.

I'll take a look at some other XJs that are for sale & see how many mpg they get & see what to do then.

If anyone has more ideas on how to get better mileage I'd still like to hear it.

BlackCat01 said:

My 01 runs about 12 city with new plugs, o2 sensors. I have heard several others also state that about 13 is the best they get for city driving. New it is listed as 16 MPG City so that is best case. I am sure you can get a few more MPG out of it but I would not count on it.

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Sounds like you have a problem with your 01. Just like I posted over in another thread, I get 15-16 city, 17-18 highway, with the a/c on...and i'm on 31's with stock gearing.

Also remember driving style plays a big role. Lots of real short distance trips or stop and go driving really does kill the mpg's.

UNCC_99XJ said:

Sounds like you have a problem with your 01. Just like I posted over in another thread, I get 15-16 city, 17-18 highway, with the a/c on...and i'm on 31's with stock gearing.

Also remember driving style plays a big role. Lots of real short distance trips or stop and go driving really does kill the mpg's.

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That pretty much covers it. My automatic also gets 15 city and around 18mpg at 65mph ( a bit more at 55mph and a bit less at 75mph) hwy with 31's and stock gears. When it was stock I got 15 city and 21 hwy.

I have done no engine mods and the engine and chassis will be turning 198K soon.
I use 10-30W oil, 75W in the gears. Stock intake box, and stock type exhaust. I replaced the plugs, cap and rotor some 50K ago, and the rear O2 sensor last fall because it smashed into the floor boards and broke.

I don't drive like a crazed loony though. It people don't like how fast I'm going they can pass me. Same thing with taking off from lights.

XJ Stryker said:

Really hmmm maybe it is cause mine is Renix but i get right at 18 MPG city... Your XJ gets as good a MPG as my Commander.

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Im calling BS on you getting 18 mpg in the city. I can see that as combined, or highway, but around town thats highly unlikely.


Specs on your Jeep?

Starboard M said:

Im calling BS on you getting 18 mpg in the city. I can see that as combined, or highway, but around town thats highly unlikely. Specs on your Jeep?

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X2,Unless your stock!
2 years ago we went to Sturgis(3500 miles) and got 22.5max-15.5min(on 5"+ and 32x10.5's and 4.10's/we had the bikes trailered out)!This July Im towing my pop-up to Ouray,CO for our run July 26th-Aug 2nd.Im really interested on the mileage for that that run based on the current gas prices.Theres a pretty good group from AZTTORA coming up also.It will be interesting!

my '01 only gets about 13 in the city as well

Zuki-Ron said:

That pretty much covers it. My automatic also gets 15 city and around 18mpg at 65mph ( a bit more at 55mph and a bit less at 75mph) hwy with 31's and stock gears. When it was stock I got 15 city and 21 hwy.

I have done no engine mods and the engine and chassis will be turning 198K soon.
I use 10-30W oil, 75W in the gears. Stock intake box, and stock type exhaust. I replaced the plugs, cap and rotor some 50K ago, and the rear O2 sensor last fall because it smashed into the floor boards and broke.

I don't drive like a crazed loony though. It people don't like how fast I'm going they can pass me. Same thing with taking off from lights.

Click to expand...

Pretty much the same with me, only i'm at 110K, have a flowmaster cat back, and magnaflow cat as my exhaust. Engine is bone stock. I too use 10W30 Mobil 1 in the engine and standard 75W in the differentials.

People do get annoyed at me when i'm taking off from a light....but tough crap. With gas at $4/gallon, i'll be driving as slow as it takes to get the best fuel economy that I can.

Im getting 13.5mpg city on stock gearing and 32s, hopefully when I change the gearing, o2, tuneup, and fuel filter it will get up to 15-17. WIth these gas prices the fuel economy is KILLER