Clogged Catalytic Converter Options

[barterj]

Last summer the first catalytic converter melted and clogged the second one. I punched out the second and replaced the first one since that is the one with 2 oxygen sensors connected to it. Since I replaced the cat I've put about 20K miles on my car. The cat. melted and got clogged again.

Does anyone know any reason(s) why this is happening?
-220K miles (2.2L)
-Engine is running at normal temp, never over heats
-Doesn't burn hardly any oil, maybe half a quart every 3,000 miles.
-It is eating gas, though i think that was from the cat being clogged and it needing extra to keep the engine running under the increased back pressure from the clogged converter.

Here is a pic of what it looked like before I punched it out today

[barterj]

Thanks for the responses

Things I know aren't wrong with the car (done or checked recently)
-Wires
-Plugs
-Compression
-rotor
-cap

Things I think could be wrong
-Air intake temp sensor
-Bad oxygen sensor, but this would send a code and there aren't any codes.
-Bad injector

How do I check the oxygen and mass airflow sensors. I assume if they are weak, not bad, they can still throw off the air fuel mixture.
Anyone know what the resistance specs are for these sensors?

This post has been edited by barterj: May 20, 2012 - 7:12 PM