Adding an O2 Sensor question

[Accelo]

As a general statement a single O2 sensor it typically used with TBI.
Dual sensors on Port or direct injection.
The system is more precise when it is basically looking at two four cylinder engines. This way the computer can modify one side's air to fuel ratio at a time.
Works great till you switch plugs on the O2 sensors side to side.... Then it goes nuts.
Any aftermarket system will have recommendations for how many and where the O2's should be located. If it's a transplant duplicate the factory set up as close as possible.
Rick