very poor gas mileage

Hey everyone.Just bought a '94 yj 4 cyl automatic on 31" and im getting just less than 10 mpg(not very happy).My 4wd light is on but i checked and im not in 4wd.It idles great and the plugs look good so i believe it may have something to do with this 4wd light.Though I seem to have a little throttle hesitation in certain gears.Not sure if its just that the 4cyl isn't very powerful.Any Ideas?

With the 2.5L turning 31's it's working really hard. Does the Jeep have the stock 4.11 gearset? You might want to look into some 5.88's or something to get the RPMs up on the roadway.

Also, if your O2 sensor has failed it could cause a rich condition; is the inside of your tailpipe black and wet? If so, your mixture is too rich and I'd bet the O2 sensor is the culprit.

thanks for the info,and yes i did notice the black moist tailpipe so I'll give it a try.

Cool; good luck glad to help out.

Also, if your O2 sensor has failed it could cause a rich condition; is the inside of your tailpipe black and wet? If so, your mixture is too rich and I'd bet the O2 sensor is the culprit.

Where exactly is the O2 sensor and how do I check it ?

It's in your exhaust. Not sure about your 94, but some vehicles have one just before the catalytic converter, some on both sides of the cat. You'll have to get under the vehicle and follow the exhaust to find it.

There's electronic methods to check the O2 sensor, but I'm not sure of them. But the backyard mechanic method is to unplug the wires leading to it (securing them somewhere of course) and drive the vehicle for awhile, measuring MPG. If the mileage goes back up then you know the O2 is bad....hopefully this will work on your vehicle also.