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

Engine 157.9, 276.8, 278.9 in model 217, 222 (except 222.163/173) 

Function requirements for deceleration fuel shutoff, general points 

• Circuit 87M (Engine management ON)
• Engine runs
• Accelerator not operated
• Gear range "D" or "R" is engaged
• Gear range "N" engaged (for a stationary or a rolling vehicle)
• 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
• Reduction of fuel consumption
• Optimization of the 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 over drive train CAN (CAN C1)

Deceleration fuel shutoff, function sequence 

In decel mode the ME-SFI [ME] control unit switches the cylinder 1 to 6 fuel injectors (Y76/1 to Y76/6) (for engine 276.8) or cylinder 1 to 8 fuel injectors (Y76/1 to Y76/8) (for engines 157.9, 278.9) dependent on the coolant temperature, the engaged gear and the engine rpm, when 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.

To prevent an abrupt increase in torque when combustion kicks in again after deceleration fuel shutoff, the ME-SFI [ME] control unit temporarily "retards" the ignition angles of the cylinder 1 to 6 ignition coils (T1/1 to T1/6) (on engine 276.8) or the cylinder 1 to 8 ignition coils (T1/1 to T1/8) (on engines 157.9, 278.9).

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.