ZRJ '00 Cherokee XJ

So..if this is somewhere else please link me and I'll go to that thread.


I have a 2000 Sport that I bought used. When I got it the guy had 31" "street" tires. Gas mileage was pretty bad even for an XJ. Like 13.5 mpg.


This past week installed a 3" BDS lift, 32" Mickey Thompsons and the mpg has dropped to about 12-12.5.


After researching...I'm wondering if it needs to be regeared. From what I could find online the factory tires were 215/75r15 which is 28.8" tall.


Would going to the 32" tires contribute to the mpg drop? It also feels very sluggish, or likes its really having to try to go over 65. Could it not be regearing and something else under it I should be checking? This is my first lift so I'm not sure what I need to be looking for as a potential problem.


Would regearing help this? I know nothing about regearing and will take it to a shop. Which then I ask..what's the best type of shop to go to to have this done?


I've also installed a Magnaflow muffler since I've gotten it with no help for the mpg issue. And I'm not expecting 20 mpg, but I thought 16 would be realistic. What else can I do? Bored throttle body? New coil packs?


Thanks for any help.

SeriousOffroad

Here ya go....
http://www.grimmjeeper.com/gears.html

93gc40

Between the lift and the tires, your sure to loose a few MPGs. Add in the high flow muffler that means even more mpg loss. Yes you need lower gearing.

Atmos

wut? everything I've come to know about airflow is a lie?


I've never understood the "spend $800 on a regear to so I can save on gas" guys. if you're running 32's, you might as well be running stock tires IMO. so go put your stock tires back on and sell the 32's so you have some gas money. plain and simple.

andrewmp6

Try a full tune up and better driving habits.

Kingfisher

Taller tires cause your odometer to turn slower, So your mileage is probably a little better than it shows.

Kingfisher

Don't think I've ever heard this.

srb531

a regear to 4.10 or even 4.56 w/ 32's will get your mpg back near stock, plus it wont have that loss of power feeling anymore . is it auto or man. trans ? i would go 4.56 w/ 32's. plus you can get the speedo drive gear changed to keep the speedo correct, but the gear change might bring it back to right. any 4wd shop can do the regear, i would get a few quotes on the job .

93gc40

More air flow also means more fuel flow.. as the computer is always trying to maintain the same Air/fuel ratio, through all conditions. So if you increase airflow, the computer will increase fuel flow to pervent a LEAN condition. The inverse applies when you increase Fuel via bigger injectors, ect. the ECU will decrease fuel flow and in some systems airflow to prevent a RICH condition.

cleenrob

Has your speedo gear been changed? If its the stock one then your speedo will be off by about 15% or so

Atmos

did I just get schooled? I didn't know our computers were anywhere near that smart

torque062

I don't think so. I can't imagine a muffler making so much of a difference that it affects fuel trims so drastically. Maybe if you are doing a dyno run going from open header back to full exhaust.

However, a header, high flow cat, AND performance muffler would more than likely affect your fuel trims enough to see a noticeable difference in mpg.

Atmos

yeah I was pretty sure most engines require a programmer to change that sort of thing. self tuning computers on an XJ.. laugh