Overrun Mode Fuel Shutoff, Function - GF07.10-P-1014MRH

Engine 274.9 in model 205.047/053/054/147/247/253 

Engine 274.9 in model 253.354/954 

The partial function "deceleration fuel shutoff function" is viewed and described from the view of the engine management for the internal combustion engine.

The deceleration fuel shutoff of the internal combustion engine is primarily activated at speeds > 160 km/h. For speed < 160 km/h the internal combustion engine is usually disconnected from the drive through opening of the wet clutch and switched off since this is the most effective from an energy point of view.

If a greater deceleration is to be realized by the drive than the electrical machine (A79/1) is capable of providing, then the deceleration fuel shutoff is also active under 160 km/h.

Function requirements for deceleration fuel shutoff, general points 

• Circuit 87M (Engine management ON)
• Hybrid drive system "READY"
• Accelerator not operated
• Internal combustion engine running
• Vehicle speed > 160 km/h or < 160 km/h and no regenerative braking possible
• Gear range "D"
• Not too high an exhaust temperatures

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 ME-SFI [ME] control unit (N3/10) performs a deceleration fuel shutoff depending on the following sensors and signals:

• Coolant temperature sensor (B11/4)
• Accelerator pedal sensor (B37), accelerator pedal position
• Crankshaft Hall sensor (B70), engine RPM
• Fully integrated transmission control unit (Y3/8n4), gear range over drive train CAN (CAN C1)

Deceleration fuel shutoff, function sequence 

In deceleration mode, the ME-SFI [ME] control unit switches off the fuel injectors for cylinders to (Y76/1 to Y76/4) dependent on coolant temperature, engaged gear and engine speed, if the accelerator pedal is not actuated.

The fuel injectors are switched on again when the accelerator pedal is operated.

The ME-SFI [ME] control unit also uses the left and right intake camshaft solenoids (Y49/4, Y49/5) and the left and right exhaust camshaft solenoids (Y49/6, Y49/7) to adjust the camshafts to a position with reduced valve overlap. This allows secure combustion without misfires.

After deceleration fuel shutoff, the ME-SFI [ME] control unit enriches the fuel/air mixture by briefly lengthening the injection period in order to relieve the catalytic converters of enriched oxygen.

In order to prevent a sudden torque rise when combustion is restarted after a deceleration fuel shutoff, the ME-SFI [ME] control unit briefly shifts the ignition angles of the ignition coils (T11 to T14) towards "retard".

Deceleration fuel shutoff is disabled when exhaust temperatures are too high, since the high oxygen content occurring in the exhaust during a deceleration fuel shutoff could cause increased oxidation of carbon monoxide and hydrocarbon (afterburning). The heat so generated can overheat the catalytic converters.

	Electrical function schematic for deceleration fuel shutoff		PE07.10-P-2714-97FBH
	Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-P-9998MRH