Ford Mustang/Capri 1979-1988 Repair Guide

Catalytic Converter System



See Figure 1

All models, including Canadian, are equipped with a catalytic converter system to meet 1975 Federal and California emission control standards. California models are equipped with two or more converters, while models sold in the other 49 states and Canada have at least one unit. The catalytic converter works as a gas reactor, which speeds up the heat producing chemical reaction between various exhaust gas components. In so doing, the catalytic converter reduces air pollutants in the engine exhaust. The catalyst material, contained inside the converter, is made of a ceramic substrate that is coated with a high surface area alumina, and is impregnated with catalytically active, precious metals. The conventional oxidation catalyst, containing Platinum and Palladium, is effective at converting noxious emissions of hydrocarbons (HC) and carbon monoxide (CO) into harmless carbon dioxide and water. A three-way catalyst, containing Platinum and Rhodium, is also effective against hydrocarbons and carbon monoxide, as well as nitrogen oxides (NOx). If a vehicle's engine is properly tuned, a catalytic converter is designed to last at least 50,000-100,000 miles before replacement, although it may last indefinitely if not subjected to prolonged overheating and overly rich fuel mixtures.

Besides the variety of underbody catalytic converters, many vehicles utilize one or more light-off converters. These auxiliary catalytic converters are mounted forward of the underbody converter(s), and are often an integral part of the front pipe assembly. They are designed to operate effectively at engine warm-up, before the main converter reaches the temperature required for maximum efficiency.

In order to maintain the converter's oxygen supply at a high enough level to promote oxidation, the oxidation catalyst requires the use of a secondary air source. This is provided by the Thermactor air injection system.

Lead-free gasoline must be used on all converter-equipped vehicles.

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Fig. Fig. 1: Dual catalytic converter


For removal and installation of catalytic converters, refer to Engine and Engine Rebuilding of this repair guide.