Overrun mode fuel shutoff, function

S07.10-0050-79

Function requirements for deceleration fuel shutoff, general points

 Circuit 87 (Engine management ON)

 Engine running.

 Vehicle rolling.

 Accelerator not operated

 Selector lever position "D" or "R"

Deceleration fuel shutoff, general

Deceleration fuel shutoff in deceleration mode of the engine has the following tasks:

 increasing the braking effect of the engine.

 reducing fuel consumption.

 improving exhaust characteristics.

The CDI control unit (N3/28) performs an overrun mode fuel shutoff depending on the following signals:

 Coolant temperature sensor (B11/4)

 Accelerator pedal module (B37/4), accelerator pedal position

 Crankshaft Hall sensor (B70), engine speed

 Fully integrated transmission control (VGS) electric controller unit (N15/11), drive range over drive CAN (CAN C)

Deceleration fuel shutoff, function sequence

If the accelerator pedal is not actuated (zero quantity delivery), deceleration mode is triggered. The CDI control unit switches off the fuel injectors (Y76) in overrun mode depending on the coolant temperature, the engaged gear and from an engine speed > 1,600 rpm.

The CDI control unit also lowers the fuel pressure in the rails over the pressure regulating valve (Y74). If the accelerator pedal is actuated or the engine speed decreases to under 1,600 rpm, the CDI control unit actuates the fuel injectors again. The fuel pressure in the rails is thus increased through the actuation of the quantity control valve (Y94) or the pressure regulating valve depending on the type of regulation.

However, if the conditions for teaching in the injector zero quantities are fulfilled, the fuel pressure in the rails can be increased up to 1,000 bar in overrun mode.