What causes a catalytic converter to fail and/or plug up? I have been wondering for some time, and just recently was reminded to ask if anyone had info on the topic.

I would think that over time, it just rust insides. Basically causes it to fall apart inside and possibly block everthing. This is what I'm thinking happens, I don't have any scientific or real mechanical data to back me up. All I know is you could hit my converter and it would rattle pretty bad inside. I didn't have any performance anymore. Soon as I my friend gutted that sucker, everything was back to when I first bought the car. Had power again and everything.

Following is a partial quote from about.com. It's accurate enough for this discussion.

There are two ways a converter can fail, it can become clogged or it can be poisoned.

When catalytic converters fail they normally clog up with debris and block the flow of exhaust gas from getting out of the system. This will cause tremendous performance problems. In extreme cases it will prevent the vehicle from starting at all. Most of the time it just limits engine performance by choking the flow through the engine.

A catalytic converter relies on receiving the proper mix of exhaust gases at the proper temperature. Some engine oil additives or engine problems that cause the mixture or the temperature of the exhaust gases to change reduce the effectiveness and life of the catalytic converter. Leaded gasoline and the over-use of fuel additives can shorten the life of a catalytic converter considerably. Even some gasket sealers and cements can poison a converter.

A catalytic converter can also fail because of certain other factors. A number of problems could occur to the catalytic converter as the result of an engine that is out of tune. Any time an engine is operating outside proper specifications, unnecessary wear and damage may be caused to the catalytic converter as well as the engine itself. The damage is often the result of an incorrect air/fuel mixture, incorrect timing, or misfiring spark plugs. Any of these conditions could lead to a catalytic converter failure or worse.

Norm

I am enlightened... thanks norm...

Great post, Norm. Excellent information!