MPG Q's

Hello, I have a 93' cherokee sport with an automatic trany, 4.0L engine, 4.5" of lift and 32/11:50 BFG tires......my MPG is pretty bad.....as expected with lift and tires, I was just woundering if you guys had any suggestions on upgrades that will help better my MPG......oh, I do have a heavy right foot while driving (it's a habbit more then anything) uh I do have the high flow K&N intake, performance exhaust (3" tail pipe, muffler, and brand new cat.), and I have a throttle body spacer. I was thinkin of getting the Jacobs off road ignition (if anyone has used this or knows someone who has please let me know how well it works) for better power and MPG.......but yeah any other suggestion other then what I have would be great! thanks

Have you regeared yet. With 32's at least 4.10 even better 4.56.

how are you measuring mpg. if you didnt change speedo gear your mileage will be off. did you regear the diffs for the larger tires. if not your probably not in the in the correct rpm range for maximum performance. i wouldnt mess with the ignition except for maybe new wires. try a new O2 sensor.

Regear.

I have the same exact setup as you - 4.0L, automatic, 4.5 lift, 32's, TBS, header, K&N, and am lead footed. I originally regeared it with 4.10's and my mileage went from stock 19 mpg to 12 mpg. I regeared again (held everything else constant) to 4.56 and my mileage went back up to 17 mpg. Made a big diff and drives much better.

I haven't re-geared yet......(money issue), I recently read a few other posts on the same topic and one thing I found out is my tire pressure was way off, I thought when they were shipped to me they were supposed to be pre-airedup so I never checked the pressure untill just the otherday........all the tires were pretty much sitting at 10-20 psi, so I air'd them up to 50 and I have notice a good change in MPG that way.

as others said gearing. But one thing i knowtice is the 3in exaust. going that big on a 4.0hurt you more than helped trust me i know this from experience. heck my big block tow rig only has a 3in single. 2.25 to a 2.5 is all you need unless your blown or have a turbo.

Not enough information

What do you consider "pretty bad" MPG?

my 200k 1989 4.0/ AW4 on 33"x12.5" was getting about 17-18 (corrected) but with a new O2 and plugs this summer, I got 1-2 more.

My mileage didn't change much going from 3.55 to 4.56 and adding a couple inches (4 to 6.5)

The AW4 has a lockup torque convertor...if yours isn't locking up (or if you drive it in the 'zone' where it cycles back & forth between locked & unlocked) it might make for bad mileage. Maybe try driving with the tranny in 3rd for a tankful (or use 4th just for high speed highway cruise) and see if it helps or hurts...

'almost flat' tires will kill the MPG and kill your tire tread...trust me I know be sure to check PSI once a week or until you are 'sure' that they hold air.

50 psi is too much pressure. Stcok tires run at 30. With bigger tires you need less -- 26 to 28 would be about right.

Regearing is the answer, but I also noticed the comment about the 3" exhaust. The 4.0L needs some back pressure to operate efficiently. A 3" exhaut is fine on an engine that turns 8,000 RPM -- which yours doesn't. That big exhaust is part of what's killing your gas mileage.

The bottom line is that your gas mileage sucks because you've got a 4.5" lift and 32" tires that are 11.5" wide. The added height increases aerodynamic resistance, you've got more rolling resistance from the wider tires, and the larger diameter and weight of the tires also adds more inertia to the drivetrain. If you get anything over 15mpg consider yourself very lucky unless you drive like a grandmother and cruise at 55mph.
Regearing to 4.56's will help a little and performance mods won't help at all. The only thing that'll really help your gas mileage is to go back to the stock setup. Only then will you get anything close to 20mpg. I'm averaging 21mpg in 50/50 city/highway driving, and on the highway I usually cruise at about 80-85mph.

I have a 92 xj 4.0L auto running 31 x 10.5 GY MTR's and I average about 17- 18 mpg with 30lbs of pressure in tires.

I don't think the 3" exhaust helps you at all. Probably your tire pressure was hurting you also.

I recently changed my exhaust to a straight pipe into a cherry bomb and then out through the tail pipe. I noticed my MPG were down to 13-14. Does this have anything to do with it? If it does I would think that the 3" exhaust on yours is overkill. Hope this helps