General System Description

Fig. 152 Emission Control Unit Inputs And Outputs (Carbureted Engine):

These vehicles are equipped with Electronic/Emission Control Units which use electronic sensors as inputs, use logic circuits to make the decisions required to lower emissions and effect smooth engine performance, and apply these decisions as outputs to various devices and solenoids to effect the changes.
The Air Injection System is designed to improve emissions performance by supplying fresh air from the air cleaner into the exhaust manifold through the air suction valve.
The Anti-Afterburn Mixture Control Valve senses intake manifold vacuum change during gear change or deceleration, and supplies fresh air into the intake manifold in order to prevent the escape of unburned fuel.
The Choke Opener System is designed to promote easy starting. When starting the engine, manifold vacuum is directed to the choke opener; thus the choke is opened a fixed amount. However, when cranking the engine, the cranking leak solenoid valve is activated and manifold vacuum to the choke opener is bled off to the air cleaner so the choke opener does not open the choke.
The Electronic/Emission Control Unit makes all of the decisions to control emissions and deliver good smooth engine performance.
The Feedback Control System is designed to provide stoichiometric air-fuel ratio, allowing the three-way catalytic converter's performance to give a simultaneous reduction of hydrocarbons, carbon monoxide, and oxides of nitrogen. This system has three sub-systems, the X-system, the M-system and the idle feedback control system. It provides air to the intake manifold to lean the air-fuel ratio which has a relatively rich setting.
The Idle Control System (automatic transmission only), maintains a stable idle speed under different engine load conditions. Idle control is accomplished using two throttle controllers, the idle boost throttle controller ( with A/C, this controller has a dual diaphragm) and the throttle controller. The solenoid valve control unit monitors the inputs and directs voltage to the three solenoid valves: Idle Boost Solenoid Valve, A/C Idle Boost Solenoid Valve, and Frequency Solenoid Valve C.