XJ14x

Hey bros,

I know "its a jeep" but im just curious if there are any tips or tricks on getting out of the 14-15 mpg mileage range with the 4.0?

Orlo

Oh holy crap!

DO NOT START THREADS ON THIS SUBJECT IN THIS FORUM!

Cue the dudes who claim they're getting 27mpg with a 4" lift and cold air intake.

Here's the best tip I got. Coast as much as you can. Use brakes sparingly and pretend there is an uncooked egg between your food and the go pedal. Otherwise. Forget it.

XJ14x

haha i hear you man. with gas being so cheap it makes it easier to swallow

jbsjunk

At this point, turn the key off. I've been told 15 is average. I only get 12, but mine has a carbed small block.

nakosd

Don't use the AC unless you're dying.
Cruise in 4th (40mph minimum) gear on city streets.
Short shift at about 2k RPM.

A good radiator is also vital. If you've got an old radiator and your temp is always sitting close to 210, then it might be clogged and could be a good time to replace it. I put a Murray single channel radiator in my XJ and it works incredibly well. I can cruise city streets and the temp stays 1-2 notches below 210 which is nice. An engine running cool is more efficient to a limited degree.

I don't know if your 1990 is carbed, but if it is, try running a can of seafoam through it to help clean up anything that might be in there.
Also keep your tires properly inflated. Especially during colder times, the tires tend to sag a bit more at the sidewalls. Having an additional 2-3 psi would be alright.

andrewmp6

Driving habits,Up keep on the jeep and don't carry around a ton of extra junk you don't need.

XJ14x

my 1990 is fuel injected

AbbadonTD

then clean the fuel injectors, that can be a whole mph right there.

You dont buy a 26 year old car for the gas mileage.

Cooling can really help. It depends on how hard you are pushing it, it helps a ton on highways. I pushed my 95 BARELY over 20, but that was a manual, and I removed the AC entirely, and installed a bypass pulley.

jcollege

Pump the tires up to 44psi also...or just buy a Prius

MtnGoat

There was a guy that claimed keeping the tank always above half full helped keep the fuel cooler and boost MPG's.
I switched to Bosch Gen III injectors and was disappointed. Ran a bit better...
Tried slotting the Crank Position Sensor. Nothing

I believe the ONLY way is to change the maps in the ECM. But no one is touching that these days.

XJ Classic

We average a real 18.5 mpg combined and driving at speed limits ( not lite on the pedal) in our 2001 4.0L auto & command trac. But no big lift , just 1.5" over stock, 29" tires.. I just finished 10 recorded tank fills after the items below were completed

What seemed to add the most value looking back over the years on items that actually increased fuel economy
Cleaning out the fuel system with Seafoam twice year
High flow Magna Cats, Banks torque tube header and Banks cat back 2 1/2 piping
Bosch Gen 3 fuel injectors, 4 spray type
Full synthetic fluids (Motor, t case, differentials)
Running 36 psi in tires
Clean Champion copper plus old school spark plugs ( NGK are better )


Also:
Well maintained suspension & drive line ( u joints, wheel bearings, ball joints, tie rods) I call it TLC tighten, lub & clean... Also agree with the others, must have a good cooling system to assure the XJ runs between 200 to 210 F


BYW no cold air intake, just the stock box with a clean filter..


I am thinking about going to 3 electric fan and remove the mechanical set up for the benefit to maintain 200 F running temp year round and less energy required without the clutch fan... Not yet convinced it is cost effective... Any one had experience with this?


Hope this helps

Ralph77

I did something similar in an '00. Picked it up cheap and fixed most of the issues. Was getting about 13 MPG so decided to see what I could do. Replaced all 4 O2 sensors. Justified it thinking they were original, had a 150K on them, and needed to go. Did a 4 hole injector upgrade. Swapped out my front and rear diff fluids for synthetic. Valvoline VV975. Cleaned my IAC and throttle body. New Champion Copper Tops. Went with these because I did not have any misfire or heatsoak issues that people talk about so when I went to swap the plugs I told myself whatever was in there she was getting new of. New tires. 225 75 15 Cooper Discovery HT's. Probably doing 16 maybe 17 around town and 22 MPG on a longer highway run. Now this is just a DD, totally stock, and never wheeled. I am older now those days are over. Still gotta own a Jeep though.

SteveMongr

Tune up.
Swap steel wheels for alloy.
Make sure wheel bearings are in good condition and brakes do not stick.
215 size highway tires.
Remove roof bars.
Air dam should be in place.
There is a lot of parasitic drag in the XJ. As mentioned, all components of vehicle need to be in good shape.

mschi772

Wow, this thread isn't that old and already there is some just straight WRONG advice being offered (running at 210 is NOT worse for MPG than running cooler; the opposite for the most part actually). Some of the advice offered as improving MPG actually has no effect on MPG (703/789 injectors vs stock for example).

I've been over this subject at length previously, and I have no intention of repeating a discussion that lasted for months and was so thorough. Go to http://www.jeepforum.com/forum/f11/m...5-ats-1551782/. Don't just read the first few posts. Read through the whole thread. Charley3 makes some leaps of logic that I disagree with, and to this day I don't believe that he is getting the mileage he is claiming to get, but the thread is still dripping with great MPG info you won't find anywhere else. Yeah, I know it is long, but you will only scratch the surface if you think post #1's summary is good enough.

Orlo

Want better mileage? Buy a Prius for all of your driving except for when you NEED the XJ. Otherwise, just drive it and worry about something else.