Catalytic Converter
The catalytic converter is made of an aluminum oxide honeycomb coated with materials like platinum and palladium that react and remove CO and HC. A two-way catalytic converter works by oxidizing CO (carbon monoxide) and HC (hydrocarbons or unburned fuel) to carbon dioxide and water. A three-way catalytic converter also removes NOx (nitrogen oxides) from the exhaust.
When a vehicle is running rich the catalytic converter is working harder and running hotter than it was intended. This heat can damage the substrate and cause it to melt and degrade. The result can be excessive back pressure caused by a clogged catalytic converter. Sometimes the substrate will become loose. If the converter rattles when tapped with a plastic hammer it must be replaced.
An easy way to test a catalytic converter for a rich fuel condition is to use a pyrometer to compare the inlet and outlet temperatures. A pyrometer is a handheld infrared thermometer used to measure temperature from a distance. At normal operating temperature the outlet temperature should always be more than the inlet. If this temperature is in excess of 200°F the engine is likely running rich. Symptoms of a clogged catalytic converter include a loss of power and the vehicle will be extremely sluggish because of the restricted exhaust flow.
Use a back pressure tester to confirm test for a clogged catalytic converter. Remove an upstream oxygen sensor install a back pressure tester. Usually the specifications will require back pressure to be below 1.0 psi. at idle and no more than 4 or 5 psi.at snap throttle. There's a big difference between a late model vehicle and an older model. Always check with vehicle manufactures specifications.
