I have read thru quite a few threads concerning A/F guages not reading correctly mainly because the o2 sensor runs cool when using an upgraded exhaust system which tend to cool the exhast gasses down, which in turn can affect Oxygen Sensor performance.

To combat this, a self-heated (3 wire) o2 sensor can be installed, to ensure proper operation regardless of exhaust temp, and also provide shorter times to closed loop operation.

You will notice the heated o2 sensor has two white wires and one black. The white wires can be interchanged, polarity does not matter. One must go to a good clean ground, either on the body or the engine block, and the other must go to a 12V switched ignition source (Power w/ the key in the "RUN" position). Any "hot" wire in RUN only will work. It can't be HOT all the time, or you will drain your battery.

The black wire goes to the stock PURPLE wire that originally went to your one-wire Oxygen sensor. This is the signal wire to the ECM.

Here is a schematic:

 

Would members care to share part numbers of 3 or 4 wire o2 sensors that have resulted in good readings after swapping out the sensor.

Theres only a couple that I have run across on the net:

Used in a 93 R1:
Napa part # OS204 for 86 Ford Escort, $39, 3 wires, black to O2 sensor, two white to power and ground.

Also this one but no part number info:
4 wire sensor from Pep Boys for $36.99. 2 white wires (positive and ground for the heating element) black (signal) and grey (sensor ground). Sensor is for a '98 camaro and it's a Borg Warner part.