oscilloscope traces /HO2 sensor

Hi All

I was wondering if someone has an instruction for testing the engine management system with a scope.

The reason for this is to find a cause for high CO emission on my old (1996) Rover 416 si. ( It's 0.5 on CO but HC and lamda have passed).

Last year I changed CAT and CO didn't changed much. I 've given up on old mantra: " arrive to MOT test station after driving on dual carriage way - blah- change oxygen sensor , CTS …" without knowing if it helps- usually it doesn’t.

Now, armed with a scope, I have tested oxygen sensor with oscilloscope- and it seems that HO2 sensor produces a reasonable signal with 0.8 V in amplitude and responses correctly, I think, to accelerator pedal - sharp changes of HO2S signal. However, I haven't figured out a way to see how ECU( or ECM) is responding to the HO2sensor signal or I haven't tested how it's working in a close loop with HO2 sensor.

There are no other visible problems- it starts well , idle rpm goes down after warming up, fan on the radiator also kicks in, spark plug are clean with tan-ish colour.

Thanks

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