Catalytic converter problems are commonly caused by lead contamination, overheating, and extended service. A damaged catalytic converter is pictured in Fig. 32-11. It would block exhaust flow.
A clogged catalytic converter, resulting from lead deposits or overheating can increase exhaust system backpressure. High backpressure decreases engine performance because gases cannot flow freely through the converter.
After extended service, the catalyst in the converter can become coated with deposits. These deposits can keep the catalyst from acting on the HC, CO, and NOx emissions. Increased air pollution can result.
The inner baffles and shell can also deteriorate. With a pellet type catalytic converter, this can allow BB-size particles to blowout of the tailpipe.
Monolithic (honeycomb) catalytic converters must be replaced when the catalyst becomes damaged (overheated) or contaminated (use of leaded fuel or extended service).
Testing catalytic converter
A four-gas exhaust analyser can be used to check the general condition of the catalytic converter. Follow the specific directions provided with the analyser. Warm and idle the engine. With some systems, you may need to disable the air injection or pulse air system. Measure the oxygen and carbon monoxide at the tailpipe.
Basically, If O2 readings are above approximately 5 percent, you know there is enough oxygen for the catalyst to bum the emissions. However, if the CO readings are still above about 0.5 percent (other systems operating properly), then the catalytic converter is not oxidising (burning) the emissions from the engine. The converter or catalyst could require replacement.
NOTE! Before condemning a catalytic converter, refer to a service manual. It may give added information on checking other systems before converter replacement.
Catalytic converter replacement
Sometimes the catalytic converter is made as an integral part of the exhaust pipe. With this design, the converter and pipe may have to be replaced together. However, with many cars, the converter can be unbolted separately, as in Fig. 32-12. When installing the new converter, use new gaskets and install all heat shields.
CAUTION! Remember that the operating temperature of a catalytic converter can be over 700°C. This is enough heat to cause serious burns. Do NOT touch a catalytic converter until you are sure it has cooled.