DESCRIPTION
The air injection system reduces Hydrocarbon (HC) and Carbon Monoxide (CO) emissions by supplying filtered air to exhaust manifold. On Pulsar NX and Sentra, the system consists of air temperature sensor, air injection control solenoid valve, air injection valve, air cleaner and water temperature sensor. The Electronic Control Unit (ECU) coordinates function of air injection valve. On Pulsar NX SE, the system consists of an air injection valve, air temperature sensor, coolant temperature sensor and thermal vacuum valve.
On Maxima and 200SX SE, system includes an air injection valve, air injection control solenoid valve, pressure regulator control solenoid valve, water temperature sensor and Electronic Concentrated Engine Control System (ECCS) control unit. The air injection valve is controlled by the ECCS control unit, corresponding to engine temperature.
Scheme 7
OPERATION
The air injection system sends secondary air to exhaust manifold. Secondary air is drawn into exhaust manifold in direct proportion to available vacuum.
AIR INJECTION VALVE
The Air Injection Valve (AIV) is a dual reed type check valve. When exhaust pressure is lower than atmospheric pressure, valve opens and secondary air is sent to exhaust manifold. When exhaust pressure is higher than atmospheric pressure, valve closes and secondary air injection is shut off.
AIV CONTROL SOLENOID VALVE
The AIV control solenoid valve cuts intake manifold vacuum signal for AIV control. The solenoid valve actuates in response to an ON/OFF signal from ECCS control unit. When solenoid is off, vacuum signal from intake manifold is cut. As ECCS control unit outputs an "ON" signal, coil pulls plunger downward, and feeds vacuum signal to AIV control valve.
THERMAL VACUUM VALVE
The thermal vacuum valve detects engine coolant temperature by means of wax expansion and opens and closes air passage from air cleaner. When air passage is closed, carburetor vacuum signal is applied to diaphragm of EGR valve. This actuates taper valve connected to diaphragm.
Scheme 8
Note. For testing, see ELECTRONIC CONCENTRATED ENGINE CONTROL SYSTEM article in the COMPUTERIZED ENGINE CONTROLS section.