I just replaced my cat converter because it was plugged. My gas mileage seemed to be significantly dropping so we thought maybe replacing the converter would solve it. Of course it didn't and I decided I should change a sensor. I've been told to replace the upstream because the plugged converter could have caused damage to those ones but I'm just looking for your guys' opinion. Which one should I replace to improve my gas mileage? I've got a 16 gallon tank an I'm getting about 170 per tank. Thanks guys. By the way I have a 1994 Cherokee.

 

Replace the one between the cat and motor. The o2 sensor after the cat does nothing in respect to how the Jeep runs. Its just there to be sure the cat is working.

 

Alright I'm only 16 and don't know too much. Can I replace it from under the car or under the hood?

 

The upstream O2 is the one that works with the PCM to regulate injector pulse width. It has the most to do with fuel economy. The rear O2 mostly monitors the efficiency of the cat.

The front O2 is in the down pipe in front of the cat. It will probably be easiest to reach from under the vehicle. When I changed mine, I did it from underneath. Make sure to use the right socket and it usually helps to use a torch to heat the bung before attempting to remove the old O2.

 

Do u or did u have a check engine light displaying on the dash? Usually, if the light is on, the system stores a trouble code number and the number can be retrieved by plugging a code reader into the ALDL port under the dash. The number(s) give an indication of what may be wrong/where to start looking. I believe OBD-I '94 models only have 1 O2 sensor located in the exhaust/drivers side of motor and serviceable from below.

 

The check engine light Came on and off before I replaced the cat converter. After fixing that it hasn't come on. That was about a week ago.

 

Might come in handy to see if a code is still stored/find out what it is.

 

Easy way to pull it is with the right size socket or wrench of course ,but do it when your exhaust is still hot if you don't have a torch, just don't touch it.

 

Well I talked to the mechanic who did my converter and apparently my o2 sensors are fine. So I guess I just get mad mileage?

 

It could be one thing, could be a combination; bad alignment+old air filter+under inflated tires, for example. You're not gonna get great gas mileage, but 10-11 mpg's seems low. Mine dropped to 17, I changed the plugs and the muffler (it was time), bumped back up to 19.

 

Well my alignment is fine and so is the tire pressure. I know the filters and spark plugs were replaced 6000 miles ago but that was one year ago. The lady that owned it before me didn't drive it much. Could the car sitting have done anything?

 

A car that sits does atrophy, things get gunky, often people don't keep enough gas in them in the cold. New plugs, but what about the wires? Battery been tested? Start small, run some Sea Foam (or treatment of choice), maybe change the plugs-things happen, they're cheap. It could be alot of things but it doesnt read serious. Honestly, I'd do a full tune-up if you haven't done one since purchase. Just clean her out, cheapest place to start since she's not giving you anything to go on. Though it may very well give you nothing more than peace of mind.

 

That's what I'm thinking. I just want to do a full tune up on it just to see if it changes anything. And if it doesn't then oh well, new equipment.

 

No promises, but previously owned vehicles are their own mystery, best to always assume the maintenance wasn't up to your standards. Blessedly mine only had 30k miles at purchase, now at 150k and still runs like new. The only thing I do "different" is run a bottle of Slick 50 thru it at every oil change. You may want to check the forum in regards to other engine cleaning tricks. Again, a vehicle that sits...just not good for them. There are a multitude of maintenance/improvement methods posted by people smarter than me.