OK

et al,
A side benefit to testing the 02 sens output by removing the vac hose to the fuel regulator is that by seeing a change in the voltage of the 02 sensor when doing so also indicates that the fuel reg is working....when the vac hose is taken off , the fuel pressure goes up, so the engine naturally runs richer... so...if , with a good sensor, there is no change when putting the reg vac hose on and off, you can assume the reg is not regulating..[aside from other fuel pressure probs]