• 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.

Poor Mileage

duntov

NAXJA Forum User
Location
Las Vegas, NV
Would a old cat/O2 sensors cause poor mileage. I have a 98 with the 4.0 with 96,000 miles on it and I am getting around 12 mpg. Of course I have a 3" lift and 31s but I would figure it would get a little better than that.

Should I replace those parts? I may just go from the manifold back...
 
Need to base line it first, plugs, cap, rotor, wires, disconnect the battery and reset the ecu, then take it for a long drive to set the parameters, don't just start it and let it idle, drive it. It will run like crap for a while but then the settings take over, see what happens. I have my original O2 and Cat in my 98, second engine, almost 400,000mi.
 
i have a 97 with the same set up and i get the exact same mileage with corrected speedo and well kept and relatively new tune up parts high flow cat performance exhaust K&N FIPK fire power ignition upgrade relativley new both 02 sensors replaced within the past 2 years synthetic oils in everything and ran the BG full system cleaner by a trusted shop and they said it didnt really need it by their judgement of how much white smoke came out the tailpipe while running it through (the more white there is = the dirtier the enigne was) id did all this trying to get better mileage and non of it really helped. if its never been replaced since the vehicle was new then it couldnt hurt to replace it before it causes a problem for you but some of the jeeps get crappy mileage and some people get lucky and get a golden goose that gets great mileage. only real hope for u is go back to stock tires or re-gear the axles
 
You may be down an MPG or two which could be tuneup related but what you are experiencing for your rig is not that much off the mark as others have mentioned. Yes, a lazy 02 sensor can cause a bit of a dropoff as well. They can be tested it if you are up for it but unless you have a check engine light, it's not real far out of line. The front 02 sensor would be the one that would affect mileage, the rear one is basically designed to measure cat converter efficiency.
 
Back
Top