Emission Control Systems: Locations

Upstream & Downstream Solenoids
The upstream and downstream solenoids are located on a bracket attached to the left inner front fender panel. These solenoids are controlled by the MCU and distribute air to either the catalytic converter or the exhaust pipe. For the CEC system to operate properly, all related systems and components must be operational.

Idle Relay
The MCU energizes the idle relay, which in turn energized the idle solenoid, which allows vacuum to operate the Sole-Vac vacuum actuator.

Idle Solenoid
The idle solenoid allows the vacuum to operate the Sole-Vac vacuum actuator, which is used to increase idle speed. The idle solenoid is actuated by the MCU by means of the idle relay.

Sol-Vac Throttle Positioner
This unit which is attached to the carburetor, consist of a solenoid and a vacuum actuator. The vacuum actuator is activated during engine start up and during deceleration to increase engine idle speed. The holding solenoid is activated when accessories such as the air conditioner or rear window defogger are operating to increase engine idle speed.

PCV Valve Solenoid
The PCV valve solenoid is installed in the PCV valve hose. It is energized by the MCU to turn crankcase ventilation when engine is at idle speed. The solenoid will also momentarily energized when the ignition switch is placed in the off position to prevent air from entering below the throttle plates.

Mixture Control Unit, 4-150
The mixture control unit is an integral part of the carburetor. This solenoid is operated by the MCU and is used to provide the proper air/fuel ratio by controlling the amount of air allowed to mix with the fuel. During open loop operation, the mixture control solenoid will allow a programmed amount of air the air/fuel mixture. During closed loop operation, the MCU will operate the mixture control solenoid to provide more or less air for the air/fuel mixture, depending on engine operating conditions.

Stepper Motor
The stepper motor, integral with the model BBD carburetor, controls the metering pins that vary the size of the air bleed orifices located in the carburetor body. The motor moves the pins in and out of the orifices in steps, according to the control signal generated by the MCU. The motor has a range of 100 steps, but the normal operating area is in the mid range. When the metering pins are stepped in the direction of the orifices, the air/fuel mixture becomes richer: when stepped away from the orifices, the mixture becomes leaner.