See Figures 1 and 2
The catalytic converter is a muffler-like container built into the exhaust system to aid in the reduction of exhaust emissions. The catalyst element consists of individual pellets or a honeycomb monolithic substrate coated with a noble metal such as platinum, palladium, rhodium or a combination of them. When the exhaust gases come into contact with the catalyst, a chemical reaction occurs which will reduce the pollutants into harmless substances like water and carbon dioxide.
There are essentially two types of catalytic converters: an oxidizing type and a three-way type. The oxidizing type is used on almost all 1975-80 models with the exception of those 1980 models built for California. It requires the addition of oxygen to spur the catalyst into reducing the engine's HC and CO emissions into H 2 O and CO 2 . Because of this need for oxygen, the AIR system is used with all these models.
The oxidizing catalytic converter, while effectively reducing HC and CO emissions, does little, if anything in the way of reducing NOx emissions. Thus, the three-way catalytic converter was developed. The three-way converter, unlike the oxidizing type, is capable of reducing HC, CO and NOx emissions; all at the same time. In theory, it seems impossible to reduce all three pollutants in one system since the reduction of HC and CO requires the addition of oxygen, while the reduction of NOx calls for the removal of oxygen. In actuality, the three-way system can reduce all three pollutants, but only if the amount of oxygen in the exhaust system is precisely controlled. Due to this precise control of exhaust oxygen content which is necessary for this system to operate properly, it can only be used in cars equipped with an oxygen sensor (feedback) air/fuel control system.
There are no service procedures required for the catalytic converter, although the converter body should be inspected occasionally for damage. Some early models with the V6 engine require a catalyst charge at 30,000 mile intervals (consult your Owner's Manual).
- Use only unleaded fuel. Use of leaded fuel in catalytic converter equipped vehicles will quickly clog and destroy a converter.
- Due to the extreme temperatures a converter will reach. Avoid prolonged idling; the engine should run no longer than 20 min. at curb idle and no longer than 10 min. at fast idle.
- Do not disconnect any of the spark plug leads while the engine is running. The raw fuel which will be expelled from that cylinder will damage the converter.
- Make engine compression checks as quickly as possible.
Testing the catalytic converter in the field is difficult as it necessitates sampling the exhaust gasses from the system both before and after the converter. This would require drilling an additional hole in the exhaust system of most vehicles covered in this guide and is not desirable under most circumstances.
The 2 reasons catalytic converters normally fail is from clogging (coating of the noble metals) or damage. Clogging could occur from use of leaded gasoline or from the use of silicone sealer which is not approved for use on engines with oxygen sensors. Damage could occur from a physical blow (contact with a curb or pothole) that collapses the converter structure or from overheating.
The chemical reactions which occur inside a catalytic converter generate a great deal of heat. Many converter problems can be traced to fuel or ignition system problems which cause unusually high emissions. As a result of the increased intensity of the chemical reactions, the converter literally burns itself up.
As long as you avoid severe overheating, physical damage and the use of leaded fuels or unapproved sealer it is reasonably safe to assume that the converter is working properly.