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Improving Mileage on Lifted '99 XJ

devildog0 said:
I'd kill for yalls mileage. Stock 95 XJ (upcountry height) w/235s and I'm averaging 13 mpg lol.

Cracked header replacement is scheduled for this weekend.

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Click to expand...

A cracked header may allow air to enter the exhaust, and if upstream of the Oxygen sensor, create a high Oxygen reading, which will cause the motor brain (ecu) to needlessly enrichen the fuel mixture, resulting in poor mileage.

Good luck, keep a jeepin!
 
Making decent progress. Got the motor mount replaced too.

8afc2e87f267381c7b125b2ce91711a6.jpg
15d0cd906a219bf8a3ac089746bd4696.jpg


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I think xj's are just too square, and the 4.0 is too old school to get good mileage. And since we all do so much in the way of armor, drivetrain and body mods to make them good wheelers... That they end up becoming super heavy, even less aerodynamic and more fuel thirsty.
A comparison-

My 2001 with 4.56's, 4 speed auto, 33's, tons of armor and 4 inch of lift gets a consistent 200 miles to a tank. I just changed the timing chain, but I haven't calculated any fuel mileage gains yet. I have a high flow exhaust, bored throttle body and 4 hole injectors. It makes decent power, but the mpg is just... so bad. 12.5 average.
It looks like this- Basically a brick with a tractor motor.
Untitled by Sean Mitchell, on Flickr

On the other hand, my 2004 Grand Cherokee has a 4.7HO engine... 3 inch lift, 3.73 gears, 5 speed auto, and 32's. It has a TON of power, and it also has a more aerodynamic body. It consistently averages 15.1 mpg, and it is way more fun to drive. weights the same as the built xj. Modern engine, easier to push through the air. I have seen 320 miles to a tank. It looks like this- (Overall it is about 2 inches taller than the xj.)
Big Bar by Sean Mitchell, on Flickr
 
srmitchell said:
I think xj's are just too square, and the 4.0 is too old school to get good mileage. And since we all do so much in the way of armor, drivetrain and body mods to make them good wheelers... That they end up becoming super heavy, even less aerodynamic and more fuel thirsty.
A comparison-

My 2001 with 4.56's, 4 speed auto, 33's, tons of armor and 4 inch of lift gets a consistent 200 miles to a tank. I just changed the timing chain, but I haven't calculated any fuel mileage gains yet. I have a high flow exhaust, bored throttle body and 4 hole injectors. It makes decent power, but the mpg is just... so bad. 12.5 average.
It looks like this- Basically a brick with a tractor motor.
Untitled by Sean Mitchell, on Flickr

On the other hand, my 2004 Grand Cherokee has a 4.7HO engine... 3 inch lift, 3.73 gears, 5 speed auto, and 32's. It has a TON of power, and it also has a more aerodynamic body. It consistently averages 15.1 mpg, and it is way more fun to drive. weights the same as the built xj. Modern engine, easier to push through the air. I have seen 320 miles to a tank. It looks like this- (Overall it is about 2 inches taller than the xj.)
Big Bar by Sean Mitchell, on Flickr
Click to expand...

I like the wheels on the XJ, what are they off of?
 
Black1990jeep said:
A cracked header may allow air to enter the exhaust, and if upstream of the Oxygen sensor, create a high Oxygen reading, which will cause the motor brain (ecu) to needlessly enrichen the fuel mixture, resulting in poor mileage.

Good luck, keep a jeepin!
Click to expand...
I think my fuel mileage actually got worse after my header replacement 🤣🤣🤣



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Am I the only one here that doesn't think the mpg is really that bad? Or rather that a brand new car today really isn't that much better?

I get 15-17 in my XJ stock up country with a ton of weight (bumpers, winch) and 29" tires. You guys getting 15 with 33"s isnt that bad IMO.

If you look at brand new Cherokees today they are getting ~30mpg highway out of the factory at $25k for a base model. Yeah thats twice as good, but if you do the math at $4/gal you'd have to drive 150k miles before you make your money back compared to a $5k XJ! I doubt a new Cherokee would last 150k miles LOL, and that's stock with no extra weight and no lift!
 
I did not buy any of my XJ Cherokees for their gas mpg's, I bought them for their simplicity, rugged reliability, ease of repair, and solid axle 4x4 capabilities. One is my trail rig, and one is daily driver.
 
With 2" OME lift & Duratracs I think I average about 17/18 mpg.

Worst was about 13mpg wheeling in snow.

Best on road trip was about 20/20.5

While the XJ doesnt make great fuel economy, it does have a look and feel that can't really be found in newer Jeeps. And that's why, while I could afford a new Cherokee with better mpg, I'll stick with the XJ.
 
bwinter1946 said:
I believer those are JK Rubicon wheels.
Click to expand...

I wonder how he worked out the different lug Bolt Pattern?

Not to Hi-Jack & keep this thread on track, I will say that my 01XJ with 3.5" RE Lift, Drop brackets, Nates F/R Bumpers, 285x75x16's on Moabs, regeared to 4.56, Correctly set up speedometer & I get 13MPG "No matter how I drive it".
 
I have done a ton of work to my rig. It has a 4.7L stroker with the low rpm cam, headers, 2.5" exhaust, 21 lb injectors. It is lifted around 6" with 35's. I get right at 20 mpg at 75 on the freeway here in Colorado. It drops to 17 when I pull my teardrop in the mountains. I run a snorkel. I find it helps the power and mileage as well on the highway. I have an AFR gauge and built an adjustable MAP sensor and I dial the mixture for a 14 or so on the highway.
 
I tried multiple models of 4-hole injectors (settled on 007's for overhead computer accuracy), and as many others have long preached, there were no real/tangible improvements to fuel economy. The most significant improvements were had in fixing exhaust leaks, followed by dropping about 1.25" off of my lift. I know the lift reduction helped, but there's no doubt in my mind the exhaust leak was robbing me the most.
 
Last edited:
I just bought a totally stock 1998 and the Overhead Console calculates gas mpg's. OHC says that for an 8,991 mile elapsed trip, the previous owner got 15.3 mpg's. As with almost all XJ Cherokees, there is a small crack in the exhaust manifold.
 
Last edited:
The AX15 is the best change to improve MPG. You have to change gear ratio's to compliment the tire size change...many do not. The 4-hole injectors may improve MPG a little. I know a few people that live near me that have installed the newer hemi engine injectors and I thin these are 6-hole...too costly for me.
 
I upgraded to multiport injectors and i'm getting 18-19 miles per gallon in a slightly lifted jeep cherokee stock gearing.
 
MaineJeepGuy said:
I upgraded to multiport injectors and i'm getting 18-19 miles per gallon in a slightly lifted jeep cherokee stock gearing.
Click to expand...
Are you going by the overhead console MPG calculation? If so... I'd do a proper test (fill the tank til automatic pump shutoff, reset your trip odometer, burn said tank, refill at the same pump til auto-shutoff, and do the math). The most commonly-used 4+ hole injectors have considerably higher flow rates, meaning shorter injector pulses are required... said injector pulse width is used by the overhead computer for MPG and range calculations.

As stated in many other threads, you *may* see smoother cold starts at most, but real fuel economy improvements are likely due to your previous injectors having been a bit long in the tooth.
 
Tim_MN said:
I just bought a totally stock 1998 and the Overhead Console calculates gas mpg's. OHC says that for an 8,991 mile elapsed trip, the Jeep got 15.3 mpg's. As with almost all XJ Cherokees, there is a small crack in the exhaust manifold.
Click to expand...

Where is the crack(s) typically located?
 
Usually in a weld at a tube Y joint, or at the collector joint.


.
standard.jpg
 
When correcting for 31" wheels (which are actually only 30" diameter), I'm sitting right at 15.5 mpg with a mix of city and highway driving. 2000 XJ with 4.5" lift, new O2 sensors, new plugs, new coil pack, 180F tstat, relatively fresh air filter, all fluids recently changed.
 
Update: After a tune-up, a fresh 195* thermostat, and some deferred maintenance issues cared for, and with a different driver, the "new" 98 gets 17.4 mpg with mostly highway driving.
 
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