Overheated Catalytic Converter
An overheated catalytic converter is often the result of excess hydrocarbon (HC) in the exhaust stream. This condition is caused by unburned fuel entering the catalytic converter and then burning. Notice that each of these conditions have one thing in common. They result in unburned fuel entering the exhaust stream. This is because the most likely cause for a clogged or damaged catalytic converter is excess unburned fuel (HC) in the exhaust.
Fuel Injectors: Leaking or dripping fuel injectors result in unburned fuel entering and burning inside of the catalytic converter. This excessive fuel in the converter results in overheating and melting of the substrate. A clogged fuel injector will result in lean burn. Lean burn occurs when there's too much air in the combustion chamber. This results in a misfire and excess hydrocarbon (fuel) entering and burning inside of the catalytic converter.
Misfire: Anything that causes a misfire or excess hydrocarbon (HC) in the exhaust will result in catalytic converter overheating. Check the distributor, sparkplug wires, and sparkplugs in distributor ignition systems. Check the coils, sparkplugs, associated wiring, and the PCM in today's EI distributor-less and COP ignition systems.
Oxygen Sensors: An oxygen sensor collects information regarding oxygen content in the exhaust stream and sends a voltage signal to the PCM. This is used to adjust the air fuel ratio. It could be a faulty sensor. If an oxygen sensor is faulty and sending a signal informing the PCM to enrich the fuel ratio, a rich fuel mixture will result.