Overrun Mode Fuel Shutoff, Function - GF07.10-D-1014TSC

Engine 642.8 in model 907 

Block diagram 

Function requirements for deceleration fuel shutoff, general points 

• Circuit 87 (Engine management ON)
• Engine running.
• Vehicle rolling.
• Accelerator not actuated.
• Selector lever position "D" or "R"
• Vehicle not in TEMPOMAT operation (with code MS1 (TEMPOMAT)) or DISTRONIC operation (with code ET4 (DISTRONIC PLUS))

Deceleration fuel shutoff, general 

Deceleration fuel shutoff causes the drive wheels to transmit a braking torque to the engine via the transmission. This increases the braking effect of the engine (engine brake).

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

• Coolant temperature sensor (B11/19)
• Crankshaft position sensor (B70/1), engine speed
• Accelerator pedal module (A68), accelerator pedal position, via powertrain control unit (N127) and drive CAN (CAN C)
• Clutch travel sensor (B109) (for manual transmission with code MJ8 (ECO start/stop function)), via powertrain control unit and drive CAN
• Clutch pedal switch (for manual transmission without code MJ8 (ECO start/stop function)), via powertrain control unit and drive CAN
• Top clutch pedal switch (for manual transmission without code MJ8 (ECO start/stop function)), via powertrain control unit and drive CAN
• Fully integrated transmission control (VGS) electric controller unit (N15/11) (with code G42 (7G-TRONIC PLUS)), drive range via drive CAN

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 dependent on the coolant temperature, the engaged gear, and at an engine speed of > 600 RPM.

The CDI control unit also lowers the fuel pressure in the rails via the pressure regulating valve (Y74/6). When the accelerator pedal is pressed or the engine speed drops to < 1,600 RPM, the CDI control unit again actuates the fuel injectors and increases the fuel pressure in the rails via the quantity control valve (Y94/4) or the pressure regulating valve, depending on the type of regulation involved.

If the conditions for learning the injector quantities are fulfilled, the fuel pressure can be increased to up to 1,000 bar in overrun mode.

If the clutch pedal as actuated for manual transmission, the overrun mode fuel shutoff is broken off or suppressed.