>  The O2 sensor is not working correctly. It shows an
> erratic output ranging from 0.3 volts to 1.8 volts.  The readings don't
> change when the mixture is enriched with the fuel pressure regulator.

Sounds like a bad O2 sensor.

> The engine runs the same when in open the O2 sensor is connected or not.

That is correct. Your O2 sensor is shot. Since your 02 sensor is not
putting out a voltage that is in an acceptable range ( according to what
the ECU expects to see), it simply ignores the 0s sensor input.

TomC