How many O2 sensors

I was wondering how many O2 sensor are the in the back by the cat conveter, i am having bad fuel mileage, i changed the fuel pressure regulator and i'm still having the problems. so do you think changing the O2 sensors would be good..........i changed the one in the front about 2 months ago... Any help would be appericated.

A scan and a graphing scan will tell you if the sensors are weak or you are just spending money here on guess work. The post cat sensor has no affect on performance.

Where can i get a scan or graphic scan done at ?

Most good garages out there have a scanner or scope capable of looking at 02 sensor activity, obviously a dealer does, but this may cost up to 1 hour labor at the going rate.

just one quick question, there are two sensors....right ? One upfront and one in the back

just one quick question, there are two sensors....right ? One upfront and one in the back

Yes, for each cat.

Autozone Stores, I think, gives you a free scan! At least the ones around here in Central Jersey do. Hope that helps!

There should be 2 of them,one in the exhaust manifold and one behind the cat.Do not take to AutoZone(really called AutoJunk),they do not use a scan tool,they use what is called a code reader.