Catalytic Converter: Description and Operation

Catalytic Converter


Due to exterior physical similarities of some catalytic converters with pipe assemblies, extreme care should be taken with replacement parts. There are internal converter differences required in some parts of the country (particularly vehicles built for the United States with strict emission requirements) and between model years.






A band clamp (3) is used to connect the joint between the two components (2 and 4). Four support hanger rods with rubber isolators (5) are used to support and isolate the exhaust system. A flexible joint (1), integral to the catalytic converter (2), allows for engine movement.






The 3.8L engine (A) three way catalytic converter is connected to the exhaust manifold by the use of flex joint and a gasket. The catalytic converter outlet connects to the muffler and resonator assembly and is secured with a band clamp. The downstream oxygen sensor is located in the catalytic converter.

The three-way catalytic converter simultaneously converts three exhaust emissions into harmless gases. Specifically, hydrocarbon and carbon monoxide emissions are converted into water and carbon dioxide. Oxides of nitrogen are converted into nitrogen and oxygen. The three-way catalyst is most efficient in converting HC, CO and NOx at a air fuel ratio of 14.7:1.

The oxygen content in a catalyst is important for efficient conversion of exhaust gases. When a high oxygen content (lean) air/fuel ratio is present for an extended period, oxygen content in a catalyst can reach a maximum. When a rich air/fuel ratio is present for an extended period, the oxygen content in the catalyst can become totally depleted. When this occurs, the catalyst fails to convert the gases. This is known as catalyst "punch through."

Catalyst operation is dependent on its ability to store and release the oxygen needed to complete the emissions-reducing chemical reactions. As a catalyst deteriorates, its ability to store oxygen is reduced. Since the catalysts ability to store oxygen is somewhat related to proper operation, oxygen storage can be used as an indicator of catalyst performance. Refer to the appropriate diagnostic information for diagnosis of a catalyst related diagnostic trouble code.

The combustion reaction caused by the catalyst releases additional heat in the exhaust system, causing temperature increases in the area of the reactor under severe operating conditions. Such conditions can exist when the engine misfires or otherwise does not operate at peak efficiency. Do not Remove the spark plug wires from plugs or by any other means short out cylinders. Failure of the catalytic converter can occur due to temperature increases caused by unburned fuel passing through the converter. This deterioration of the catalyst core can result in excessively high emission levels, noise complaints, and exhaust restrictions.

Unleaded gasoline must be used to avoid ruining the catalyst core. Do not allow engine to operate above 1200 RPM in neutral for extended periods over 5 minutes. This condition may result in excessive exhaust system/floor pan temperatures because of no air movement under the vehicle.

The flex joint allows flexing as the engine moves, preventing breakage that could occur from the back-and-forth motion of a transverse mounted engine.