Jaryox

I just got a 2000 Jeep cherokee with a 4.0 and a fresh full rebuild done at a local shop. There are probably around 2000 miles on the rebuild and i saw the receipts and such; but with my normal city/hwy driving I am only getting 12.5MPG.. That's while driving economically and not going offroad. The jeep has an aftermarket air filter (like K&N), another little air filter looking thing but small on the valve cover and is lifted with 2" short arms on new 31's.

What should my order of operations be?

EvilMaster

An average stock XJ will get around 15mpg. You are getting slightly less because of your larger tires. If you want better fuel economy, your best bet would be to put some 28" street tires on it. Alternatively, you can look at upgrading your ignition system with an aftermarket performance ignition like an MSD unit. Also, you can add an aftermarket free flowing exhaust like a flowmaster setup and throttle body spacer. And of course, you should perform proper maintenance on your Jeep to ensure that everything is running as smooth as possible. Or...Buy a toyota prius or something.

Cherockee

Have you changed your speed-o gear so that your odometer is reading correct? There is probably about 10" of extra travel with each turn of the tire so if you haven't changed it you're actually traveling futher than your odometer says you are.

I suppose that if you're comparing before MGP with larger tires still on it then I would guess that something is wrong. I didn't look to see where you're from but I do know that with the colder weather we're just begining to get here in the north (actually the last couple days have been nice) I've been getting worse mileage in all my vehicles- I think the fuel mix changes around this time.

bluedragon436

I would say if you could to throw some stock sized tires on there and roll around a bit as recommended above to see what you are getting than.. now if you are looking at MPG with the larger tires on it before and now... than that is a bit different and I would look into doing the basic tune up options, run some injector cleaner through it.. which should retrun you pretty close to the MPG's you were getting with the new/rebuilt motor installed... if you want a bit more than you can upgrade parts, as was stated above, such as the throttle body spacer, freeier flowing exhaust, upgraded ignition system, better plug wires, etc... Now the thing with the aftermarket intake, TB spacer, bored TB, better exhaust, headers, etc.. is you need to reset your ECM so that it will learn and apply a fuel maps to the new setup as you drive it after upgrading these items... other wise it will still run the same as it did before just with more money poured into it.

Jaryox

This makes a lot of sense, I always felt like on the hwy when I was going 60 I was going much faster then everyone else. Thanks for the tips i'm sure ill get everything figured out and let you guys know.

I just found it strange that my friend who was on 79bronco axels, with 33" tires was getting better mileage while wheeling.. But he had flowmasters and such.

Btw EvilMaster, I will sooner die then drive around a hybrid let alone a Prius.. Thanks for the advice though. Haha

EvilMaster

I hear ya.

You'll need a 32 tooth speedo gear to fix that up with 31" tires. You can get them on quadratec.com for forty bucks. Installing it is a breeze, takes about 10 minutes. Here is a step by step guide for you.

https://docs.google.com/fileview?id=...YjJhYjY4&hl=en

freegdr

gearing will also affect mpgs

captainwoot

Possibly get better as it accumulates more miles, when the engine is "broken in" ?? just a thought.