If you can pull the plugs you can limit it to a cylinderor another system. If one plug looks black or otherwise messed up but theothers are a toasty light brown then it is cylinder specific. Black smoke is fuel vs blue smoke is oil andsteam is coolant. Once you narrow itdown to cylinder or motor you have to figure out why a system or part is notworking correctly. All sensors send avoltage to the computer so you can use a safety pin and a digital multi meterto see what the voltage is and then reference to what it should be (within)before you replace parts.
A rich condition can saturate the cat to the pointwhere the chemical reaction that changes carbon monoxide to water creates somuch heat that it damages the converter as well as the oxygen sensors. At least that’s what we were taught in autotech school but I have not seen a lot of people with this problem so no need to comeunglued about it yet.
