Replaced O2 sensor

I just replaced the upstream O2 sensor on my 96 4.0 XJ. I also did a full tune up, plugs, wires, cap, air/fuel filters and an oil change. my milage is still 14-15mpg. Is not disconnecting the battery when changing the O2 sensor a problem?

What size lift/tires? or stock?

And you do realize that most Cherokees get around 15/16 MPG in town stock that are fully tuned up.

You could try disconnecting the battery to reset the computer and see what happens.

no lift, 235 BFG AT's, which actually improved it even without calculating size difference

Is your cooling system working properly? My thermostat had broken in my XJ, and it was actually running too cool (under 150). I replaced the thermostat and flushed the system so the engine would run all the time at 200-210, and as a result I gained an additional 2-3mpg hwy.

just flushed and replaced coolant and coolant temp sensor. runs like 210ish

Was it getting better mileage previously?

I frequently forget to mention that people need to check for exhaust leaks, cracked exhaust pipes. The O2 sensor compares the exhaust gas O2 concentration to out door ambient air O2 concentrations, and if exhaust gas is blowing on the O2 sensor from a crack or gasket leak, it can throw off the measurements, and the computer will get miss led and waist fuel!!!!!!!!

Same milage as before. I know 3 other local xjs who get 17+

How many tanks since you tuned up?

http://www.fueleconomy.gov/feg/findacar.htm

Note that the feds rate the 4 cyl/5 speed high--in my experience that won't quite work out that way when driving into headwinds/up-down hills as you have to use a lot more skinny pedal to keep things moving with the 4 banger.

Mileage differs MOSTLY on how you drive, so comparing one guys mileage to yours isn't very practical. Try swapping XJs for a few tankfuls and see what you both get that way.

Tire inflation, using synthetic lubricants, and keeping your vehicle tuned will make a difference.

You WILL lose mpg if using ethanol fuels--period. The hit is about 10 percent.

You WILL lose mpg when using winter-blended fuel. Three to ten percent.

Cold starts + short drives = more fuel use.

Air conditioned? Your a/c compressor runs when the defrost is on.

How much junk do you haul on a daily basis? More weight = less mpg.

Joe, where did you get 4 banger from in this thread?

Ecomike said:

Joe, where did you get 4 banger from in this thread?

Click to expand...

It's a clarification on the ratings listed at the site he linked. They compare various engine/trans MPG for given year/make/model of vehicle.

Bdiddy11 said:

What size lift/tires? or stock?

And you do realize that most Cherokees get around 15/16 MPG in town stock that are fully tuned up.

You could try disconnecting the battery to reset the computer and see what happens.

Click to expand...

I have had 2 (one I still have, the 89, 130,000 miles, 2wd) that gets about 19 to 20 mpg as DDs in Houston (24 hyw). My 87 was down to 6 mpg (11 mpg hyw) winter when I first bought it. Now it averages about (or did before I replaced the AW4, new mileage pending) 15-16 (278,000 miles, 4wd). Both are stock.

The single largest improvement I got on MPGs was a 6 mpg gain on a new O2 sensor. It was like night and day.

You should disco the battery and reset the pcm so it can learn with the new sensor.

I tend to think the idea of the computer "re-learning" is overstated, especially on a DD. After a few driving cycles is the old data not already pretty much out the window? Not sayin' pulling the batt cable doesn't make it happen faster, I'm just sayin'...