When you say you deflected the sensor plate, did you only push down on it? If so, you would not have seen a change in the duty cycle since the system is already at the rich limit and can't do anything more. Try grabbing the nut in the center of the plate and pull up while checking duty cycle. Pulling up on the sensor plate will lean out the mixture. If the duty cycle changes, then readjust the mixture at the adjustment screw on the air meter assembly. If not, then it will be necessary to measure the voltage at the O2 sensor and see if it changed with mixture and find out why the rest of the system is not working (failed ECU, EHA, etc.) All this assumes that the fuel pressure readings are in spec to begin with.

Remember, with a rich air-fuel mixture, the CAT will not have enough O2 to do its job, so it will look like a failed CAT at first glance.

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Erich Loepke
2010 Ford Focus
Currently Benz-less