Peugeot 405 Manual

ACAV inlet system (16-valve models) - general information, removal and refitting
Fuel/exhaust systems - multi-point fuel injection models / ACAV inlet system (16-valve models) - general information, removal and refitting


General information
1 To ensure optimum efficiency at high engine speeds, and maximum torque at lower engine speeds, 16-valve models have an inlet manifold with a variable inlet tract system. The system is called ACAV (variable acoustic characteristic induction).

2 The inlet manifold is divided into two tracts of different length and diameter; a long tract (for low-speed torque) which is 650 mm long, diameter 36 mm, and a short tract (for highspeed power) which is 370 mm long, diameter 45 mm.

3 Situated between the manifold and the cylinder head is a line of four butterfly valves, mounted in an alloy housing. Mounted on either end of the housing is a vacuum diaphragm assembly. Each diaphragm is connected to the butterfly valve spindles via a pushrod. The vacuum diaphragms are connected to an electrically-operated solenoid valve, which is in turn connected to the braking system vacuum pump. The pump is mounted on the end of the cylinder head, and is driven off the left-hand end of the inlet camshaft.

4 At engine speeds below 1800 rpm and above 5080 rpm, the ECU closes the solenoid valve, shutting off the vacuum supply to the diaphragms, and the butterfly valves are closed. With the valves closed, the short inlet tracts are closed, and the incoming air flows only through the long inlet tract, boosting the torque output.

5 At engine speeds between 1800 rpm and 5080 rpm, the ECU opens the solenoid valve.

The vacuum present in the pump is then allowed to act on the vacuum diaphragms, which draws the pushrods into the diaphragm bodies, and opens up the four butterfly valves.

With the valves open, the incoming air is allowed to flow through both the short and long inlet tracts, for maximum power.

6 To check the system, start the engine and allow it to idle. Slowly increase the engine speed, whilst observing the vacuum diaphragm pushrods. At approximately 1800 rpm, the pushrods should be drawn into the diaphragm bodies (valves open). Release the throttle cam, and allow the engine to idle again; the pushrods should extend from the diaphragms (valves closed).

7 To check the operation of the solenoid valve, disconnect the vacuum pipe from the diaphragm. Start the engine, and allow it to idle. Place your finger over the end of the pipe; no vacuum should be present in the pipe. Slowly increase the engine speed; at approximately 1800 rpm, vacuum should be felt in the pipe. Allow the engine to idle again, and check that the vacuum supply is switched off. If this is not the case, either the solenoid valve or its supply voltage is at fault.

8 To check the operation of either vacuum diaphragm assembly, disconnect the vacuum pipe, and suck hard at the control valve stub; the pushrod should be drawn into the diaphragm body, and the valve should open.

If this is not the case, the vacuum diaphragm is faulty.

Removal and refitting
ACAV valve assembly
9 Remove the inlet manifold as described in Section 18.

10 Bearing in mind the information given in Section 7, slacken the retaining clip, and disconnect the fuel feed and return hoses from their unions on the fuel rail. Where the original crimped-type Peugeot hose clips are still fitted, cut them off and discard them; use standard worm-drive hose clips on refitting.

11 Depress the retaining tangs, and disconnect the wiring connectors from the four injectors. To avoid the possibility of the wiring connectors being incorrectly reconnected on refitting, mark each connector with its relevant cylinder number (No 1 is at the transmission end of the engine).

12 Disconnect the vacuum hoses from the fuel pressure regulator and the ACAV diaphragm hose T-piece.

13 Slacken and remove the nuts and three bolts securing the valve assembly to the cylinder head, then slide the assembly off its mounting studs and remove it from the engine compartment. Remove the valve assembly gasket from the head, and discard it - a new one must be used on refitting.

14 Examine the assembly, checking that the butterfly valves open freely and close smoothly. If not, the assembly must be renewed. The only components available separately are the vacuum diaphragm units - if either one is faulty, it must be renewed as described below.

15 Refitting is a reverse of the removal procedure, noting the following points: a) Ensure that the valve assembly and cylinder head mating surfaces are clean and dry, and fit the new manifold gasket over the studs. Refit the valve assembly, and securely tighten its retaining nuts and bolts.

b) Ensure that all relevant hoses are reconnected to their original positions, and are securely held (where necessary) by the retaining clips.

c) Refit the inlet manifold as described in Section 18.

d) On completion, check the operation of the ACAV system as described above.

Vacuum diaphragm unit
16 Disconnect the vacuum hose from the diaphragm unit. Using a suitable flat-bladed screwdriver, carefully lever the unit pushrod off the valve linkage balljoint (see illustration).

19.16 ACAV vacuum diaphragm unit
19.16 ACAV vacuum diaphragm unit

17 Slacken and remove the two bolts securing the diaphragm unit mounting bracket to the valve assembly, and remove the diaphragm from the engine.

18 Refitting is a reversal of the removal procedure, ensuring that the diaphragm pushrod is clipped firmly onto the linkage balljoint.

Solenoid valve
19 The solenoid control valve is mounted on the left-hand end of the cylinder head (see illustration). Before removing the valve, first disconnect the battery negative terminal, and position it away from the battery.

19.19 ACAV solenoid valve retaining nut (1), wiring connector (2) and hose
19.19 ACAV solenoid valve retaining nut (1), wiring connector (2) and hose connections (3)

20 Depress the retaining clip, and disconnect the wiring connector from the valve.

21 Undo the nut securing the valve to the cylinder head, then withdraw the valve, disconnecting its vacuum hoses as they become accessible.

22 Refitting is a reversal of the removal procedure. Test the system on completion, as described above.


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