Tests were carried out to discover how efficient automotive catalysts were after approximately 80,000 km of use and, by removing the catalysts from catalyst-equipped cars, to compare their raw emissions with those from non-catalyst equipped cars. Tests were also carried out to examine the effect on emissions of exhaust oxygen sensor malfunction and spark plug deterioration. Catalyst efficiencies ranged between 69 per cent and 88 per cent for hot start tests. Raw emissions of hydrocarbons and carbon monoxide from the catalyst controlled cars were lower than those from the non-catalyst car, while raw emissions of oxides of nitrogen were similar for all cars. When the exhaust sensors were disconnected, there was an immediate deterioration in the control of emissions from the three-way catalyst car; emissions from the lean-burn car with the oxidation catalyst showed little change. When one spark plug lead was disconnected there was a large increase in fuel consumption and emissions of hydrocarbons and carbon monoxide from both types of car. There was a large decrease in emissions of oxides of nitrogen from the three-way catalyst car, and little change in emissions of oxides of nitrogen from the lean-burn car. (A)

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