Chevrolet Full-size Cars 1968-1978 Repair Guide

Catalytic Converter



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Fig. Fig. 1 Single bed monolith catalytic converter

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Fig. Fig. 2 Bead type catalytic converter

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Fig. Fig. 3 Dual bed type catalytic converter

The catalytic converter is a muffler-life 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. 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 all 1975-78 vehicles. 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 on these vehicles.

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.

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 really can reduce all three pollutants, but only if the amount of oxygen in the exhaust system is precisely controlled. Due to this precise oxygen system is used only in vehicles equipped with an oxygen sensor system.

There are no service procedures required for the catalytic converter, although the converter body should be inspected occasionally for damage.


  1. Use only unleaded fuel.
  3. Avoid prolonged idling; the engine should run no longer than 20 min. at curb idle and no longer than 10 min. at fast idle.
  5. Do not disconnect any of the spark plug leads while the engine is running.
  7. Make engine compression checks as quickly as possible.


The chemical reactions which occur inside a catalytic converter generate a great deal of heat. Most 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 and the use of leaded fuels it is reasonably safe to assume that the converter is working properly. If you are in doubt, take the vehicle to a diagnostic center that has a tester.