letsgomuddin

Alright, here it goes. 2001 XJ, 4.0, AW4, 3.55 gears, 31" AT's. I get an average of 11 mpg driving like a grandma! What's going on here? I have no CEL, seems to run great, no dragging brakes or anything like that. I should be up around 16 mpg with this setup. My old TJ had 4.10's and 35's and the 3 speed auto and got 12 so I should be getting much better mileage than I am. I have a full function scanner and checked a few sensors, namely the coolant temp sensor which is working properly and the o2 sensors. I'm not sure how they should operate but they jump back and forth from lean to rich like I assume they should. Any thoughts or ideas here??

V8XJDavid

Do you have some stock size tires you can run and check your MPG with? I found on mine that when I went to larger tires my MPG went to hell.

letsgomuddin

I tried that, only gained 1 mpg

NorCalJeep

Welcome to the club. I avg 8 mpg.

letsgomuddin

I just don't understand why? I had larger tires on my TJ and more rolling weight, plus a 3 speed trans vs a 4 speed with the xj and I got better mileage with the TJ

stock95sport(for now)

The O2 sensor SHOULD go lean/rich as you say, but the trouble with them is when they get older, it happens at a much slower rate than when they are new. the faster they get readings to your computer, the faster and more efficient the changes it makes.

My '95 w 185k (when i got it) got 11mpg when driven like a Grandma. I changed all my fluids, got it running the right temp (was running cold when i got it) did a tune up (except plugs which were new when i bought it) and put a Spectre performance air filter in. Not a CAI just a stock style panel filter, but similar to the K&N. This has gotten me to about 15 if i dont hammer on it. Im gonna try O2's when i have the cash to see if it makes any difference.

letsgomuddin

o2 sensors are next then, $80 for the pair yuk! I'm only doing the 2 before the cats, no point doing the other 2 since all they do is tell the computer if the cats are bad, at least thats my understanding.

stock95sport(for now)

yeah kind of. They also let the computer know, sort of, how well the changes it makes works. At least thats MY understanding. lol. my buddy explained it to me once, but i forget exactly. In any case, the fronts are more important i believe. My XJ is a '95, i THINK i only have 2 total but their like $50 ea.

letsgomuddin

I'm one of the "lucky" ones with 4 o2 sensors!

stock95sport(for now)

And TWO CATS! probably, idk when they started that.

letsgomuddin

I had 3 cats, now down to 2!