Ihad my fuel regulator changed. Since then my gas milage has gone down to about 10 miles per gal around town. prior to the replacement I was getting about 17 mpg. Does it sound like a sensor?
Oxygen sensors on 1997 Mazda MPV
I presume the fuel pressure regulator was changed because it was leaking or allowing too much fuel to the engine. Your gas mileage is awful. I would look with a scan tool plugged into the 16 pin diagnostic port under the dash at the OBD2 information showing fuel trim figures for both banks of the engine to see if the problem is related to one or both sides of the engine ( could be a vacuum leak)and look at the engine coolant temperature sensor value if the computer things the engine is cold it will be adding fuel. A scan tool will also show O2 sensor values allowing you to see if they are in range and fluctuating properly rich to lean. The only other way to look at an O2 sensor is to look at it on an oscilloscope to see if it operating well or "hanging" rich or lean.