Air injection system (Honda Accord 3)

This device is designed to provide oxygen to the exhaust stream. Oxygen is supplied at a point in the exhaust pipe where the temperature is high enough to effectively burn off some hydrocarbon compounds. The main component of the device is an air intake valve, usually a reed type, which opens under the influence of periodic exhaust gases. In the initial position, spring pressure keeps the valve closed. When a vacuum is created in the exhaust pipe by the engine, the diaphragm is affected by the pressure difference, the spring action is weakened and the air passages open. The supply of vacuum to the diaphragm from the engine is regulated by the ECU by means of a separate electromagnetic valve. The ECU, determining the position of the vacuum switch, the temperature of the coolant and outside air, the speed of the car and the pressure in the exhaust pipe from sensors, decides when to open the intake valve for air injection.

Checking functionality

1. Let the engine idle and warm it up to operating temperature. Remove the air filter and listen to the air intake opening for hissing. There should be no sound at idle, as the intake valve should be closed.

2. If noise is heard at the air intake opening, disconnect the vacuum hose that goes to the suction valve and connect a hand pump with a vacuum gauge to the hose. There should be no vacuum in the hose. If there is some vacuum and the noise has stopped, this means that the control system is malfunctioning. If there is no vacuum and the hissing noise remains, this means that the suction valve has remained open and must be replaced.



3. To test the valve for proper operation, apply vacuum to the diaphragm on top of the valve and listen for a hissing sound, which indicates that the valve has opened while the engine is idling. To test the control system, first raise and support the car so that all four wheels can rotate freely. Place the transmission in second gear and accelerate the engine to approximately 15 mph (25 km/h). The ECU should then open the control solenoid, which will apply vacuum to the intake valve and open it.

4. If there is no vacuum at a wheel speed of about 25 km/h and the engine is at normal operating temperature, then the solenoid valve should be checked using the vacuum control box located on the heat-insulating partition. Disconnect and plug the inlet vacuum hose and create a vacuum on the solenoid valve using a hand pump. When the engine is idling (or turned off), there should be no voltage on the solenoid, and the solenoid valve should hold a vacuum. When the engine is running at a speed of about 25 km/h, there should be 12 volts on the solenoid, the solenoid valve should be open accordingly, which leads to the supply of vacuum to the intake valve.

5. If the wiring between the solenoid and the ECU is OK, but the solenoid is not receiving the proper voltage, then the ECU is faulty.