The intake shutter is mounted on the intake manifold. The intake shutter is fully open when the engine is operating. To stop the engine, the VSV operates in accordance with the signals from the ECU, and the actuator closes the intake shutter. As a result, the amount of vibration is reduced when the engine is stopped.
VSV (Vacuum Switching Valve)
Signals received from the ECU cause the VSV to switch the pressure applied to the actuator between atmospheric and vacuum pressures.
EGR (Exhaust Gas RecirculationSystem)
In the EGR system, the ECU controls the vacuum regulator valve based on the signals that are sent by various sensors, in order to operate (open and close) the EGR valve. This causes a portion of the post-combustion gases to recirculate through the intake manifold to slow down the combustion speed. This lowers the combustion temperature and reduces the generation of nitrogen oxides. Through the adoption of the diesel throttle, it has become possible to increase the intake manifold pressure in order to stabilize the EGR volume.
Vacuum Regulator Valve
The vacuum regulator valve operates in accordance with the signals from the ECU to turn ON/OFF the vacuum (generated by the vacuum pump) that actuates the EGR valve.
The vacuum that is sent by the vacuum regulator valve operates (opens and closes) the EGR valve to introduce the post-combustion gases into the intake manifold.
Operation of EGR System
The operation of the EGR is stopped under the conditions listed below in order to ensure drivability and reduce black smoke.
When the coolant temperature is low.
When the vehicle is being driven under high-load conditions.
When the engine is decelerating (the EGR operates during idle).
When the vehicle is being driven at high altitudes.
On 15B-FTE and 1HD-FTE engines, the mounting position of the EGR valve has been improved in order to prevent its performance from being affected by the intake air temperature.
On the 15B-FTE engine, a dual construction EGR pipe has been adopted. The coolant water flows along the outside of the pipe to cool the EGR gases. Thus, the intake air is prevented from being warmed by the EGR gases.
Intake Shutter Inspection
To inspect the intake shutter, connect a vacuum gauge to the diaphragm, and verify that the actuator rod moves when the specified amount of vacuum is applied to it. Measure the resistance between the VSV terminals for the intake shutter.
Diesel Throttle Inspection
An inspection of the diesel throttle consists of an inspection of the throttle motor. Remove the throttle motor connector and measure the resistance between the specified terminals.