Deceleration fuel shutoff, function - GF07.10-P-1014MMA

ENGINE 157.9 in MODEL 212, 218 

ENGINE 278.9 in MODEL 207, 212, 218 

Function requirements for deceleration fuel shutoff, general points 

• Circuit 87M (engine timing ON)
• Engine running
• Accelerator not operated
• Drive position "D" or "R" is engaged
• Gear range "N" engaged (for a stationary or a rolling vehicle)
• Vehicle not in CC mode, DISTRONIC PLUS mode (for code (233) DISTRONIC PLUS), Active Blind Spot Assist mode (for code (237) Active Blind Spot Assist) or Active Lane Keeping Assist mode (for code (238) Active Lane Keeping Assist)
• Not too high an exhaust temperature

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) (model 207, 212), coolant temperature sensor (B11/4) (model 218)
• Accelerator pedal sensor (B37), accelerator pedal position
• Crankshaft Hall sensor (B70), engine speed
• Fully integrated transmission control controller unit (Y3/8), stage via drive train CAN (CAN C)

Deceleration fuel shutoff, function 

In deceleration mode, the ME-SFI [ME] control unit switches off the fuel injectors (Y76) depending on coolant temperature, selected gear and engine speed, if the accelerator pedal is not actuated. The fuel injection valves 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 extending the injection time, in order to protect of the catalytic converters from enriched oxygen. In order to prevent a sudden rise in torque when combustion is restarted after a deceleration fuel shutoff, the ME-SFI [ME] control unit briefly shifts the ignition angles of the ignition coils (T1) 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.