GM Buick/Oldsmobile/Pontiac/Full-Size 1975-1990 Repair Guide

Catalytic Converter

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See Figures 1, 2 and 3OPERATION

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 metal such as platinum, palladium, rhodium or a combination of these. 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 is used on 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.



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Fig. Fig. 1: Bead type catalytic converter

The oxidizing catalytic converter, while effectively reducing HC and CO emissions, does nothing in the way of reducing NOx emissions. Thus, the three-way catalytic converter was developed to reduce the NOx emissions.



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Fig. Fig. 2: Dual bed type 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 control requirement, the three-way converter system is used only in vehicles equipped with an oxygen sensor system (1980 Calif. vehicles and all 1981 and later models).



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Fig. Fig. 3: Single bed monolith type converter

SERVICE



There are no service procedures required for the catalytic converter, although the converter body should be inspected occasionally for damage. Some models with the V6 engine require a catalyst change at 30,000 mile intervals (consult your Owner's Manual).

REMOVAL & INSTALLATION



Refer to Engine & Engine Overhaul for Removal and Installation procedures.

 
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