Usually a lil after the gas light comes on(99) Its due for a tune up. But that is also a mix of highway, city, and wheeling. And like I said I drive a bit 'spirited'

 

Well it looks like I might still be running rich, so probably going to replace my o2 sensor this week, as well as do a brake job and bleed the brakes.

 

A bad O2 sensor will suck your mileage right down. I have a 92 Stealth that had a bad O2 sensor, it used 1/4 tank to drive 15 miles. It has a 20 gallon tank as well so that was only 5mpg. I never got a Check Engine Light for the O2 sensor, but I was getting an injector code. I plugged my data logger into the Stealth and the O2 sensor was putting out a steady 1v signal instead of the up and down voltage it should, injectors were working as they should

Changed the O2 sensor and it is getting about 22mpg now

 

'89 4.0L, 3" lift on 235s. I check my mileage with a GPS. Around town I average 13.5 mpg and about 22 mpg on the highway if I stay between 65 and 70. The XJ gas tank is puzzling, it's claimed capacity is 20 gallons but most people struggle to squeeze 16 gallons in there. The truth is, the actual capacity is more than 25 gallons and, on occasion, I've managed to pump 20 gallons into it when the gauge indicated I already had a 1/4 tank. It seems to be dependent on the individual pump nozzle and my patience. I got 345 miles of purely city driving out of one tank, I actually went 100 miles before the needle became unglued from the far right of the gauge.

 

I've had screwy gauges in both my XJs. My 89 was lifted around 4" on 31s and could get anywhere from 300-600 miles per tank depending on weather conditions (based on MPGs between fill ups). My 90 is stock and would be hard pressed to go more than 450 miles per tank. Since the gauge is iffy for empty I try not to push it though, 300 miles is usually what I get once the gas light comes on ( not actually that empty though).

 

600 miles to a tank? wtf..... prius drivetrain?

 

40mph tailwinds will do that

 

I drive 80+ miles a day round trip to work and back (all highway). Somewhat stock with 30" duratracs, full exhaust, intake and tuner. I usually see about 320-330 a tank.

 

600 miles per tank that is BS unless it is being towed. That would be 30 mpg for a 20 gallon tank, pure BS, I get that in my 06 legacy, I have never heard of a Cherokee getting anywhere near 30 mpg's, if that was the case then Al Gore would have made the Cherokee the SUV of the year. Again no way in hell a brick going down the road is going to get 30 mpgs.

 

Yep, 30mpg. Once. Maybe you missed me mentioning a 40mph tail wind. Under normal conditions, wind at less than 5mph in any direction, 25mpg on the highway was about the best it got. This was on long flat trips.

 

Were you going down hill also? That would be 8 mpgs better than what it was rated at. If you ever got that I want to know what voodoo you did to it. I will drink the koolaid and do it to mine since the best I get is 18 mpgs with a tail wind.

 

Ask all the ecoboost f150 owners about EPA estimations. And technically yes, it was downhill. I had full header back exhaust on it, 31" ATs, and 3.55 gears. Bigger tires were accounted for.

 

Mine has a 20 gal tank, never ever EVER put more than 16 or so gallons in it, and that was on E. I think they don't use the last 4 gals in the tank. But I get about 13mpg for the 16 I put in. So 200-220/ tank. 1995 xj 3in lift with 31" Cooper Discoverer stt. 4.0l

 

There is no way you can or ever will get 600 mile per tank in an XJ unless it is being towed. YOu will never get 30 miles to the gallon no matter what kind of tail wind and driving down hill. This is total BS!!!
:b s:

 

The LAST thing I worry about with my XJ is miles per gallon. I've literally never checked it carefully. Rough estimates put it somewhere in the low to mid teens. But then my XJ is rarely out without a trailer behind it, a load of cargo or slogging through snow......which is why I don't give a ***** what my exact MPG is. You might get 600 miles per tank if you're using a 55 gallon drum to hold your fuel.