• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

gas mileage reasonable for my mods???

fordtech

NAXJA Forum User
Location
Amherst NY
97 sport, 4.0L auto, 3.55's, 4.0" lift, 31's, front skid (make a difference??), yakima loadwarrior.

Otherwise this thing is stock. I get about 15-16 MPG on the highway, around 13 city. I use to be in the 18 hi-way range. I guess 2mpg lose isnt too bad concidering the mods and rack. But compared to 20mpg that some folks got stock it was 2 mpg short to begin with.

I would like to do a few small things to increase the mpg....happy with power but more is always better! Heres what i have in mind.... new cat (current one rattles, but not clogged...yet), catback of some sort, K&N in the factory box, tuneup with thick wires, champion plugs, and good cap/rotor (needs pretty bad). I may even try my hand at hand boring the t-body, we'll see.

So, feel free to share your opinions, and your mileage.... maybe it will make me feel better to hear what others are getting :)
 
'91 Cherokee Sport with 4.0L, auto, 3.55's, 2" lift, 31's, Front/rear skid plates, Steel bumpers front & rear, roof mounted spare and hi-lift on a Yakima rack.

I am driving an almost identical setup to yours. I'm averaging 15.7 mpg of primarily weekend use and trails once or twice a month. My son gets 16.9 mpg out of his 4.0L, 5 spd, '87 Comanche which is driven all over daily and on trails.

The mod our Cherokees need that would improve gas mileage the most would be lower gears. Running 31's with stock 3.55 gears is making the engine work harder every time we start from a stop or pull up hills. It's easy to see how gears will help if you imagine you are riding your bicycle around in 10th gear. You'd have to strain hard to get it going from a stop. Same thing is happening to the engine with the big tires installed. Since I'm planning on sticking with 31's, I'll be installing at least 4.10's when I get the $$.

My son and I have done all the tune-up type things you are planning and they are probably all a good idea. But, don't expect the same mileage increase you should get from regearing. Plus with lower gears off-road manners will be a bit better too.
 
Also with 31's you're going farther with every rotation of the tire, if you haven't changed your speedo gear it'll show less distance than you've actually travelled.
 
You need to add 10% to your miles before you do your calculations. Thats pretty close to the difference in distance traveled per wheel revolution. My corrected MPG with the same tires/gears as yours is about 17 hwy.
 
im runing an 87 with auto and 4in lift 31 tire and 4:10 gear and a rack . I do about 16mpg but the power is there better that the 3:55 so you not to bad
 
It has the correct speedo gear for this combo. I also understand about re-gearing.
Im just asking if that is reasonable MPG for my setup.....which it sounds like it is.
Im not expecting magic with a tune-up and exhaust either.
 
i'd say you are "average" as far as mileage. borrow a friends hand-held GPS and use it to establish a "corrected" speed chart that shows your error in a percentage.
example:
i travel 100 miles on my odometer and it's 97.3 on my GPS. thats your odometer mileage x .973 = actual miles traveled. thats on the 31s. the 33s are 1.03%.
 
I run 4" of lift and 31" MT/R's, Auto trans (w/OD), and 3:55 gears. My GPS (Garmin Legend) shows that for every 100 miles my odometer reads, I actually travel 107 miles. That is with WAAS enabled here on the East Coast. This has been checked, rechecked, and checked again with a friend's handheld.

That said, with 31's I simply have to multiply my odometer reading by 1.07

I'm getting around 15 MPG combined city/highway but I am overdue for a tune-up. The 31" MT/R mounted to the Wilderness rack on the roof prolly doesn't do much for it either :dunno: These gas prices are going to put an end to my using the XJ as a DD :(

I am not sure why, Sidriptide, you would show more than actual mileage with larger than stock tires unless you re-geared or have changed the speedo gear??? .
 
Back
Top