Green & Yellow

Here is what I have been noticing lately. My XJ is getting between 10-12 mpg. Just filled up this morning, 14 gallons, 144 miles traveled. I am not a fast driver, I drive more like a grandpa than anything. Plus my XJ is not lifted, almost completely stock except for the tires which are 235's instead of 225's. My Jeep just turned 189k miles. So what could be causing this? Any help is much appreciated.

F1Addict

This really only matters if you've noticed a sudden or progressive drop in economy. 10-12 mpg isn't unheard of with a 4.0 and depends not only on how you drive but where you drive. Going up and down hills, idling, log roads, and snow all will affect mileage even if you're easy on the throttle. A tune-up will likely help...

Basic

Oil and filter
Air filter
Spark plugs
Cap and rotor

Advanced (basic, plus)

Plug wires
All fluids (transmission, diffs, transfer case)
Fuel filter
02 sensors
Backflow injectors
Replace all vacuum lines

Other things to check:

Tire pressure
Exhaust manifold bolts
Make sure you're in "Comfort" mode if you've got an AW4 (auto)

belvedere

All good suggestions by F1Addict. Based on experience, if tune-up parts are new or nearly new, I would replace the O2 sensor. Also, is your Check Engine light on?

DFlintstone

As it happens I just did the same tire swap. After some fumbling around I settled on 5%. So 50 MPH is 52-1/2. & about the same, 57.5, is actually about 60. It aint' much, but you can add 5% to your miles/odometer as well.

mattphillips90

well when mine says empty I really have like 30 more miles to go so you might just have a screwy gauge. I get the same gas but I'm on 36's with stock gears at the moment, I don't see any reason you should be getting that

The Rooster

at 189k even if your o2 was changed at 100k it would be on its way out... If you have not done a tune up start there.. make sure to get a brass cap and rotor.... and good wires
but f1 addict is defintely put you in the right direction

Green & Yellow

Yesterday I:
changed the oil/filter
Air filter is clean

Today I:
aired up my tires (were @ 40 psi, raised it to 50 psi, we'll see what difference that makes)

It does have an AW4, what is "comfort mode"? I run it almost always in 2wd, I have only used part time 4wd a couple of times in the snow.
I do traverse quite a few hills, but I let the engine slow down instead of hammering it up the hill. I also run about 2 miles of flat gravel road in a day.
Spark plugs were changed last year (by previous owner)
Nothing to my knowledge has been done to the cap & rotor

I have done nothing with any other fluids except topping off the coolant.
Fuel filter I have yet to find, I know I am capable of changing it, I just changed two on a tractor a few days ago. I have no idea where the O2 sensor is, I am new to "on-road" vehicles. I Know I can do all of this but I am just figuring out where everything is and what it does, it is a lot different from the tractors I have worked on.

Check engine light is off, I think I may have to swap the O2 sensor at least.

Very interesting, thanks!

I usually fill up before the gas light comes on, it has come on 1 time in the last 4000 miles.

Thanks! Looks like an O2 sensor is on the list. Any ideas on what one would cost?

DFlintstone

Get an NTK. 40-60$. (or OEM). I spent a little more to support my local guys. Spray with PB or anything ahead. (days?). I jacked my frame to let the axle hang and came in from the front on my 90. (My Renix might be different). If you chop the wires a 7/8 box wrench should fit. Agreed with the guys above, major mileage issues might be there.

You ever get your codes read? Just a thought. 02 is a great start....there are more sensors though.......

Because they are so important, knowing your 02 is right is a great start. Let us know!

(the puter' might "throw a code", if your 02 heater isn't heating).

rawk krawler

189k shouldn't be going out... I have 263k on my 95, basic tune up gives me 19mpg on 33's with 3.54 gears

DFlintstone

"with respect", I disagree. Glad you are doing so well! (puter' jockey here)

I won't mention names, but a number of seasoned members have mentioned these things fail. 60K might even be "smart". Idk if the titanium dioxide, or the Zirconia have different lives, but given the price of gas, and the certainty that they DO fail, knowing the puter' is getting the correct message on the mix makes good scene to me.

19MPG! Great Man! thatrocks!

EvstaG

Comfort mode was a "feature" installed in earlier AW4 Cherokees that was designed to allow the tranny to shift at lower RPMs, theoretically making the ride more comfortable. This caused the engine to shift at the less than ideal range, decreasing fuel economy. Later Cherokee's with the AW4 were directly wired with the "power mode" setting, for increased fuel economy

DFlintstone

Pete.. or .

cruiser54

Absolutely correct. Power mode is the one you want to use.

O2 sensors don't always just fail. They get slow to respond.

I couldn't agree more about the tune-up stuff. ALL of it. No gimmicky plugs. I like NGKs. Use them in everything.

Make sure your intake manifold bolts are snug. A vacuum leak in the intake tract can fool the O2 sensor into thinking the engine is lean, and subsequently tell the PCM to add fuel.

Give us your exact tire size, too.

This will help with driveability. Many people think that the lowest possible RPMs are best for fuel economy but that's not true. At low RPMs, with your foot into the pedal, you have low engine vacuum. You want to keep an engine in it's sweet spot where it is efficient. Try this 15 second fix next time you've got the hood opened.

https://www.cherokeeforum.com/f2/free-quick-fix-41821/

black2000xj

dont forget winter blend fuel will hurt
my jeep in the summer was getting 16-18
now im getting 12-14 mpg

i drive the same way all the time..what hurting me is im a stickler for letting my jeep warm up in the winter..and short trips

a tip...adjust your t.v. cable...it takes all of 10 seconds to do and it makes a world of difference

cruiser54

Good point on the winter blend fuel.

Do the best you can with maintenance, TV cable adjustment, Power mode, and go for it.