My son has a 92 Spirit 2.5L 4.
The O2 sensor was replaced about 1 year ago and it's now burning rich again. Black exhaust on acceleration.
I checked the connector, expecting to see battery on at least one pin to supply the heater element but no such luck. The Chilton manual only shows wire colours, not signal names ie ground, battery heater etc.
1 - Is it likely the 02 Sensor has died again?
2 - Should I see battery on any of the sensor connector pins?
3 - Does anyone have a chart of what I should see/what signals are on what pins. It would help in measuring the O2 sensor voltage.
4 - Any other thoughts, suggestions, contributions?

Thanks for the help.
Jim Brooks