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

Engine 276.8 in model 172.4 

Function requirements for deceleration fuel shutoff, general points 

• Circuit 87M (Engine management ON)
• Engine runs
• Vehicle rolling
• Accelerator pedal not operated
• Gear range "D" or "R" is engaged
• Vehicle is not in cruise control mode
• 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 signals:

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

Deceleration fuel shutoff, function sequence 

In deceleration mode, the ME-SFI [ME] control unit switches off the fuel injectors for cylinders 1 to 6 (Y76/1 to Y76/6) dependent on coolant temperature, engaged gear and engine speed, if the accelerator pedal is not actuated.

The cylinders 1 to 6 fuel injectors are switched on again when the accelerator pedal is operated.

The ME-SFI [ME] control unit also adjusts the valve overlap to its minimum value via the left and right intake camshaft solenoids (Y494, Y495) and the left and right exhaust camshaft solenoids (Y496, Y497). This ensures that an optimum conversion rate of the catalytic converters is achieved more rapidly.

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 for cylinder 1 to 6 (T1/1 to T1/6) 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.