Catalytic Converter: Description and Operation

Converter Operation

The catalytic converter system consists of pellets coated with a catalyst (activated material) such as platinum or palladium and is enclosed in a heat resistant steel case.

When the mixture of exhaust gasses passes through the catalytic converter, the hydrocarbon (HC) and carbon monoxide (CO) content of the exhaust gasses is oxidized and converted into water (H2O) and carbon dioxide (CO2). Since large amounts of unburned fuel gasses will cause the temperature of the catalytic converter to rise, a high temperature system is provided. To avoid excessive increase of catalyst temperature during long decelerations... some models use a fuel shut off system which is activated through the carburetor idle stop solenoid.

When the throttle plate is in closed position, but engine speed is higher than 2650 ± 50 RPM, fuel shut-off takes place through an electric contact on the idle speed adjusting screw and a switch.


Warning system for excessive catalyst temperature

1. If there is a malfunction which causes excessive catalyst temperature, a warning switch activates a "slow down" light on the dashboard.

2. This system consists of a thermocouple located inside the catalytic converter and of a control unit.

3. When the temperature of the substrate reaches 982° C ± 50° C (1800° ± 50° F), a signal light is activated intermittently, increasing in frequency as temperature rises.

4. The operation of the control unit is reversible and the hysteresis of the switching levels is 50° C ± 10° C (122° F ± 18° F).

5. Failure of the thermocouple is indicated by continuous activation of the dashboard light.

6. To check the operational condition of the system: put the ignition switch in the on position and activate the "Slow Down" signal light.