Deceleration air function

Acceleration air function requirements - general

 Circuit 87M ON (engine control ON)

 Engine running

Deceleration air - general

At the start of deceleration, the turbochargers continue to turn for a little time due to the mass inertia of the shafts, compressor and turbine wheels, and generate more boost pressure against the closed throttle valve.

Pressure peaks (brief howling) in the turbochargers are prevented by the deceleration air switchover valve (Y101).

Deceleration air function sequence

If the ME-SFI control unit (N3/10) detects the transition from load to deceleration mode on the signals from the accelerator pedal sensor (B37), the deceleration mode switchover valve is actuated with a ground signal.

This causes the two deceleration air valves at the turbochargers to be charged with vacuum from the vacuum reservoir. The deceleration air valves open a bypass (around the related compressor impeller), causing the boost pressure to drop immediately.

When the deceleration air switchover valve is not actuated (in charging mode), the diaphragm chambers of the deceleration air valves are connected to the intake manifold. The deceleration air valves are closed by the integrated springs and by the boost pressure in the intake manifold.

If a deceleration air valve does not close, less boost pressure is generated.



Vacuum is built up in the vacuum reservoir during the engine intake phase and in deceleration mode.

To do this, the check valve (under vacuum) opens the line between the intake manifold and vacuum reservoir.

P09.41-2530-09

12 Intake manifold

22 Vacuum reservoir

128 Check valve (vacuum)

110/4 Deceleration air valve

110a Left turbocharger

110b Right turbocharger

110d Compressor impeller

Y101 Divert air switchover valve

b Vacuum to air pump switchover valve (Y32)

B Test connection for divert air

D Intake air (downstream of air filter)

E Charge air