DESCRIPTION
This air injection system, used on 3.9L, 5.2L, 5.9L engines, adds a controlled amount of air to exhaust gases to reduce Carbon Monoxide (CO) and Hydrocarbon (HC) emissions. The system is designed so that air injection will not interfere with Exhaust Gas Recirculation (EGR) for control of NOx emissions. The air injection system consist of air pump, air control valve, (either diverter valve, relief valve or switch/relief valve), vacuum solenoid, rubber hoses, check valve(s) and injection tubes.
Scheme 33
AIR PUMP
Air intake occurs at the centrifugal fan located behind the pulley. Internal rotating vanes route the air supply into the air switching system where it is processed through the air injection system. Air pump is not rebuildable and must replaced as a unit.
AIR SWITCHING SYSTEM
Air switching solenoid is energized when vehicle is started and in open loop mode. This directs air supply upstream to exhaust manifold. In closed loop mode, air supply is diverted downstream to the catalytic converter. Downstream, the air supply will assist the oxidation process in catalyst. As loop mode changes back and forth, air supply is switched.
CHECK VALVE
Check valve is a one-way valve which allows air supply from air pump to pass through but prevents exhaust gases from backflow. This valve protects system during air pump belt failure, high exhaust pressure or air hose ruptures.
COOLANT TEMPERATURE SENSOR
The coolant temperature sensor, located in thermostat housing, monitors the cooling system and transmits a voltage signal to the computer that is proportionate to coolant temperature. The sensor's signal is used by the computer to determine correct air switching system operation.
DIVERTER VALVE
Diverter valve is used to prevent backfire in the exhaust system during sudden deceleration. Sudden increase of intake manifold vacuum causes valve to open, allowing air supply to pass through the valve and silencer to atmosphere. A pressure relief valve, within diverter valve housing, controls system pressure by diverting excessive air supply to atmosphere. (Scheme 34)
RELIEF VALVE
Relief valve is used to control maximum air pump pressure at high engine speeds. When discharge pressure exceeds approximately 9 psi, the relief valve opens to vent excess air supply to atmosphere.
Scheme 34
SWITCH/RELIEF VALVE
Switch/relief valve has a dual function. On cold start, manifold vacuum signal is sent to switch/relief valve and air supply is directed to exhaust manifold. After engine is warm, air supply is directed downstream to catalytic converter. At high speeds, vacuum solenoid cancels vacuum signal to switch/relief valve. Valve is regulated by manifold vacuum and a vacuum solenoid. When vacuum signal to switch/relief valve is canceled, most air supply is diverted to atmosphere. (Scheme 35)
Scheme 35
NO AIR SUPPLY
- Start engine and raise speed to 1500 RPM. Check air supply at rubber hoses. If air supply increases with RPM, air pump operation is okay. If air pump is okay, check for leakage at hoses and fittings. Repair or replace as necessary.
- If hoses are okay, check diverter valve for leakage. If air is expelled through diverter exhaust with vehicle at idle, replace valve. If diverter valve is okay, remove check valve. Blow air through check valve in direction of air pump. Air should not pass through. Blow air through opposite direction. Air should pass freely.
Note. For additional testing of air injection components, see appropriate article in the COMPUTERIZED ENGINE CONTROLS section.