Health check
1. Set the engine to idle and warm it up to operating temperature. Remove the air filter and listen to the air intake for hissing. There should be no sound at idle because the intake valve should be closed.
2. If noise is heard in the air intake, disconnect the vacuum hose that fits 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 noises have stopped, then this means that the control system is not working properly. If there is no vacuum and the hissing noise remains, the suction valve is still open and needs to be replaced.
3. To check valve operation, apply vacuum to the diaphragm on top of the valve and listen for hissing, which indicates that the valve has opened while the engine is idling. To check the control system, first raise and secure the machine on stands so that all four wheels can turn freely. Place the gear lever in second gear and accelerate the engine to approximately 25 km/h. In this case, the ECU should open the control solenoid valve, which will apply vacuum to the suction valve and open it.
4. If there is no vacuum at a wheel speed of about 25 km / h and normal operating temperature of the engine, 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 apply vacuum to the solenoid valve with a hand pump. When the engine is idling (or muted) there should be no voltage on the solenoid and the solenoid valve should hold a vacuum. When the engine is running at about 25 km/h, there should be 12 volts on the solenoid, the solenoid valve should be accordingly open, which causes vacuum to be applied to the suction valve.
5. If the wiring between the solenoid and the ECU is OK, and the solenoid is not getting the proper voltage, then the ECU is malfunctioning.