Emission Control Systems: Description and Operation

The purpose of the emission control system on these vehicles is to reduce CO, HC, and NOx emissions. The emission control system for these vehicles includes an altitude compensation system, air injection system, air intake temperature control system, carburetor feedback control system, exhaust gas recirculation system, hot idle compensation system, positive crankcase ventilation system, throttle body heater system, and a three-way catalytic converter.

ALTITUDE COMPENSATION SYSTEM (ACS)

The altitude compensation system increases the amount of air to the carburetor to prevent an overrich air/fuel ratio at high altitudes. The system consists of the high altitude compensator and carburetor. The high altitude compensator provides additional air bleeds for the primary main and secondary main fuel circuits and supplies additional air into the intake manifold.

AIR INJECTION SYSTEM (AIS)

The air injection system supplies secondary air into the exhaust system to burn (oxidize) CO and HC in the exhaust gas and to control the oxygen signal for the engine control unit.

AIR INTAKE TEMPERATURE CONTROL SYSTEM (TAC)

The air intake temperature control system controls air intake temperature to prevent icing and operates depending on air temperature around the control valve.

CARBURETOR FEEDBACK CONTROL SYSTEM (FBC)

The carburetor feedback system controls the air/fuel mixture to about 14.7:1, reduces CO, HC, and NOx emissions, and minimizes fuel consumption.

EXHAUST GAS RECIRCULATION SYSTEM (EGR)

The exhaust gas recirculation system introduces exhaust gas into the intake manifold to reduce NOx in the in the exhaust gas. It operates depending on engine load, engine speed, and coolant temperature.

HOT IDLE COMPENSATION SYSTEM (HIC)

The hot idle compensation system supplies secondary air into the intake manifold to stabilize idle speed when the air intake temperature is more than 67°C (153°F).

POSITIVE CRANKCASE VENTILATION SYSTEM (PCV)

The PCV valve is operated by intake manifold vacuum. When the engine is running at idle, the PCV valve is opened slightly and a small amount of blow-by gas is drawn into the engine. At higher engine speeds, the PCV valve is further opened and a larger amount of blow-by gas is drawn into the engine.

THROTTLE BODY HEATER SYSTEM (PTC)

The throttle body heater system warms up the throttle body of the carburetor to prevent carburetor icing. The system consists of the PTC heater, PTC heater relay, and the coolant temperature switch.

THREE-WAY CATALYTIC CONVERTER (TWC)

The catalytic converter is used to reduce CO, HC, and NOx. To accomplish this, the three-way converter is filled with a compound of platinum and rhodium.