95383z28

Hi, been away for a while but glad to be back in the car. I noticed that I was getting a little bit of black smoke and can smell a fuel smell in the exhaust so I figured I was running a little rich. With the engine cold and the key in the on position I was looking at the O2 voltage using the pcmcomm utility. After monitoring it for 5 minutes the mV reading went from both starting at 435mV to 4mV on the right and 150mV on the left. I switched the sensors and did it again but the readings swapped indicating that it is with the sensor and not the wiring. Is the sensor reading low bad? They are both GM sensors with low mileage.

Pete