Hey everyone, I own a jeep Cherokee sport 1998 model and I'm looking at doing a few mods to it but I wanna get the fuel economy better because I'm only getting around 400ks to a take now. I have the 4L straight 6. Can anyone recommend how to get better fuel economy.

Full ignition tune up, new air filter, all new fluids in the drivetrain, injector cleaner, clean your TB and IAC, the smallest tires you can run inflated relatively high, reducing your drag coefficient, reducing weight as much as possible.

For mods, a free flowing intake, exhaust, 4 hole injectors.

There's a thread around here or on jeepforum about somebody who's goal was to get 25mpg with 30x9.5 tires. I'm sure you could get a lot of good info there.

Here's that thread.

http://www.jeepforum.com/forum/f11/m...5-ats-1551782/

It's a long thread, but it's worth it to page through most/all of it as our discussions wandered and slowly evolved (and sometimes devolved) over time.

I bought my 2001 xj about two months ago. It had the usual problems, cruise didn't work and heater controls were in-op.

I checked the vacuum ball behind the bumper and found the vacuum line had shrunk and pulled off the nipple.

I cut it and spiced it with a short section (4") of good vacuum line. Problem solved ?

Before the repair I was getting 24 MPG driving 50 miles each way to work & back at times doing 80 MPH on freeways.

After the vacuum repair I'm getting 18-20 MPG doing the same type of driving.

Hey, it's been below freezing most of the time I've owned it so I'm glad the heater is working now. 5 MPG is worth not freezing every time I commute.

Read this link:

http://www.ehow.com/how-does_5143394...-save-gas.html

Install one of these and keep the needle in the green.....u'll get better mpg.

Keep up the service on your XJ as per the manual and keep in mind there is only so much you can do with a brick as far as MPG.

Buy an Ultraguage/Scanguage...it will track all your mpg info accurately. I get 20.5 MPG in my stock 1997 Sport Upcountry with 235/70/R16 tires and AW4. With the ultraguage you can see how much just your driving habits affect mpg. You can be cruising on the highway getting 23 mpg then stop at a stop light and watch your mpg drop a full 1 mpg in 3 minutes (Ultragauge can track your trip mpg from the time you start the vehicle to the time you turn the key off so that each trip can be monitored accurately as well as lifetime and instantaneous). Non-highway driving is the XJs enemy...these things are horrible in stop and go traffic and the open loop program on the ECU is very inefficient MPG-wise. Try to get to operating temp as soon as possible and MPGs will be better.

Which unit do u have?

Ultragauge and it is the best $60 I have ever spent. Only good on OBDII though....

Does it show tranny fluid temp?

THIS is good advise.

I do have some questions about the peak torque / optimum rpm's on our 4.0's.

Mine will stay higher in the green when I keep the RPM's higher than I would normally.

3rd gear at 3000 rpm's on the freeway seems to keep the needle the highest.

If I shift to 4th the rpm's drop down a but, by sound it sounds good, feels good but my needle will drop into the yellow quite a bit.....

Is it always best to go for the most vacuum when driving or is there a crossover point where you're better off lowering the rpms and lowering the vacuum? That's been a question I have had for a while.

What do you guys think about rpm's / vacuum for best economy?

Great question! Without getting into the details, math says that the 4.0 is most efficient around 2400-2600 RPM, yet you hear incredibly vague claims left and right that the best is the lowest possible without lugging (people who say this NEVER clearly define what "lugging" is or isn't).

This question as puzzled the crap out of me as I'm deliberately sticking to stock height and in wanting to maximize efficiency could not for the life of me figure-out if 215/75r15 (28") or 235's (29") would be ideal. Seems like such a little change, but that diameter change has a decent impact on highway cruising RPM--the 215's keep it closer to what the math wants, but the 235's lower the RPM's.

The following advice is based on my assumption that the torque converter does not lock-up when the trans is set to "3." Please correct this if I am wrong.

I don't think cruising around in "3" will help as a lot of energy will be lost/wasted in the torque converter because it is not locked, so even if doing so keeps your engine at a more efficient RPM, your rear tires will see relatively less of that energy compared to when the torque converter locks when in "D."

I thought the converter would lock in "3" under a light load, but I can't swear to that. Can someone confirm one way or the other? FWIW, we run 235/70/15 (28" tall) tires.

Maybe if shifted into "3"?