DESCRIPTION
The air injection system reduces Hydrocarbons (HC), Carbon Monoxide (CO) and Nitrous Oxide (NOx) emissions by injecting air into the exhaust system.
A belt driven air pump injects air into the exhaust port of the cylinder head, exhaust manifold or the catalytic converter. The air injection system operates at all times and will by-pass air only for a short time during rich operation, deceleration, or at high speeds.
The air management valve performs by-pass and diverter functions. The check valve protects the air pump from damage by preventing a backflow of exhaust gases.
Air Injection System Schematic (Typical). Scheme 75
AIR PUMP
The air pump is a belt driven, vane-type pump, located at the front of the engine. The air injection system uses filtered air from the air pump to promote further oxidation of HC and CO before these gases are released.
DECELERATION VALVE
This valve is used to prevent backfiring in the exhaust system during deceleration. The valve is normally closed, but it opens when manifold vacuum increases during deceleration.
The increasing vacuum overcomes the spring pressure, allowing additional air into the intake manifold to prevent an overly rich mixture from entering the combustion chambers. Air trapped in the chamber above the vacuum diaphragm will bleed, at a calibrated rate, through the delay valve portion of integral check and delay valve.
This reducing vacuum acts on the diaphragm. When the vacuum load on the diaphragm matches the spring load, valve assembly closes. This shuts off air to the intake manifold.
DIVERTER VALVE
The diverter valve is used to prevent backfiring in the exhaust system during sudden deceleration. The valve senses sudden increases in the intake manifold vacuum, causing the valve to open, and to divert air away from the exhaust system. This allows air from the air pump to pass, through the valve and silencer, out to the atmosphere.
A pressure relief valve controls system pressure by diverting the excess pump outlet air (developed at higher engine speeds) to the atmosphere through the silencer.
CHECK VALVE
The check valve prevents the backflow of exhaust gases into the air injection system. The check valve operates when the air pump by-passes at high speeds, extreme engine loads, or in case of air pump malfunctions.
ELECTRIC AIR CONTROL VALVE
This valve provides normal diverter valve function and pressure relief by diverting air into the engine air cleaner when the system pressure exceeds a predetermined value.
Valve operation is controlled by a vacuum solenoid. When the solenoid is energized, the valve operates normally. When the solenoid is de-energized, air is diverted by operating conditions.
Air is directed to the exhaust ports during cold engine operation (open loop), and to catalytic converter during warm engine operation (closed loop).
ELECTRIC AIR SWITCHING VALVE
The air switching valve is a spring actuated, 2-way valve. This valve is located in series between the air control valve, and the exhaust system.
When the solenoid is de-energized, vacuum is applied to the diaphragm chamber to provide airflow to exhaust ports.
When the solenoid is energized, vacuum to the diaphragm chamber is blocked, and the chamber is vented to the atmosphere. This allows the spring tension to open the port to the catalytic converter, and to close the engine port.
ELECTRIC DIVERT/ELECTRIC AIR SWITCHING VALVE (EDES)
The Electric Divert/Electric Air Switching Valve (EDES) combines the functions of both the air diverter valve, and the air switching valve into one integral component.
The ECM controls the air divert valve by controlling the vacuum solenoid in the EDES valve. The EDES valve will divert air during these operating conditions: rich conditions, deceleration, high RPM, and whenever ECM recognizes a problem and sets check engine light.
The ECM also controls the air switching function of the EDES valve by directing air injection flow to the exhaust ports during cold engine operation (open loop), and to catalytic converter during warm engine operation (closed loop).
Sectional View of EDES Valve. Scheme 76
PRESSURE OPERATED ELECTRIC AIR CONTROL/ELECTRIC AIR SWITCHING VALVE (PEDES)
The Pressure Operated Electric Air Control/Electric Air Switching Valve (PEDES) combines both diverter function and air switching function into one integral component.
The PEDES valve is electrically controlled by the ECM, and operated by air pump pressure. The valve's operation is not dependent on intake manifold vacuum.
For cold engine (open loop) operation, the port solenoid is energized, and the air flows to exhaust ports. In warm engine (closed loop) operation, the port solenoid is de-energized, and the converter solenoid is energized. This forces airflow to the converter. In the divert mode, both solenoids are de-energized, and airflow is allowed to vent to the atmosphere.
COMPONENT TESTING
Note. For AIR MANAGEMENT SYSTEM FUNCTION check, ELECTRIC AIR CONTROL/ELECTRIC AIR SWITCHING VALVE check and ELECTRIC DIVERTER VALVE check, see DIAGNOSTIC CHARTS in COMPUTER COMMAND CONTROL article.
Scheme 77
- Detach check valve and blow through it in direction of flow to cylinder head. Attempt to suck back through direction of flow. Replace valve if it allows airflow against direction of flow. (Scheme 77): Sectional View of PEDES Valve
- If air pump was inoperative and had signs of exhaust gases reaching pump, a failed check valve would be indicated.
- Accelerate engine to approximately 1500 RPM and observe airflow from hoses. If airflow increases as engine is accelerated, pump is operating properly. If it does not increase, or is not present, proceed to next step.
- Check for proper pump belt tension, leaky valves, seized pump, improperly routed hoses or disconnected hoses.
Note. Do not oil air pump. The air pump system is not completely noiseless.
- Remove air cleaner, plug air cleaner vacuum source, and connect tachometer to engine. With engine running at idle, remove deceleration valve signal hose from intake manifold.
- Reconnect signal hose and listen for airflow through ventilation pipe and into deceleration valve. Engine speed should drop when hose is reconnected.
- If airflow lasts less than 1 second, or engine speed does not drop, check for defective hoses or deceleration valve.
EXHAUST BACKFIRE
- Engine not tuned to specifications.
- Engine vacuum leaks.
- Faulty diverter valve or check valve.
- Electric air switching valve or air control valve not switching air pump discharge to air cleaner on start or quick deceleration.
POOR GAS MILEAGE
- Air pump output not shifting to catalytic converter upon signal from TVS.
- Faulty electrical and/or vacuum circuits.