ACAV Air Supply System (16-valve models) (Peugeot 405)

To ensure optimum efficiency at high engine speeds and maximum power at lower engine speeds, the 16-valve models feature a variable intake manifold. The system is called ACAV (Acoustic Characteristic Variable Induction).

The intake manifold is divided into two tracts of different lengths and diameters: a long tract (for low power) 650 mm long and 36 mm in diameter and a short path (for high power) 370 mm long and 45 mm in diameter.

At each end of the housing, a vacuum diaphragm assembly is installed. Each diaphragm is connected to the throttle valve axis via a pushrod. The vacuum diaphragms are connected to an electrically controlled electromagnetic valve, which in turn is connected to the brake system vacuum pump. The pump is mounted on the end of the cylinder head.

At engine speeds below 1800 rpm and above 5080 rpm, the ECU closes the solenoid valve, disconnecting the vacuum from the diaphragms, and the throttle valves close. With the valves, the short air supply paths are closed and air flow enters through the long path.

At engine speeds between 1800 rpm and 5080 rpm, the ECU opens the solenoid valve. The vacuum acts on the vacuum diaphragms and opens the four throttle valves. With the valves open, the incoming air passes through both short and long paths to produce maximum power.

Examination

1. To test the system, start the engine at idle. Slowly increase engine speed and observe the diaphragm vacuum tappets. At approximately 1800 rpm, the tappets should be acting on the diaphragms.



2. To check the operation of the solenoid valve, remove the vacuum tube from the diaphragm. Run the engine in idle mode. Place your finger on the end of the tube; there should be no vacuum in the pipe. When slowly increasing the engine speed to 1800 rpm, a vacuum should be felt in the pipe.

ACAV valve block

Removal

1. Remove the intake manifold.

2. Remove the fuel line.

3. Remove the vacuum hoses from the fuel pressure regulator and the ACAV diaphragm hose from the tee.

4. Unscrew the three bolts securing the valve block to the cylinder head and remove it together with the gasket.

5. Check that the throttle valves open freely and easily.

Vacuum diaphragm

ACAV Vacuum Diaphragm Block

Removal

1. Remove the vacuum hose from the diaphragm housing.

2. Unscrew the two bolts securing the vacuum diaphragm assembly to the valve block and remove the assembly.

Solenoid valve

The electromagnetic control valve is installed on the left end of the cylinder head.

Removal

1. Press the clamp and remove the electrical connector.

2. Unscrew the valve mounting nut, remove the valve and remove the vacuum hoses from the valve.