Overrun Mode Fuel Shutoff, Function - GF07.10-S-1014TRC

Engine 274 in model 447, 448 

except code XM0 (Facelift) 

Function requirements for deceleration fuel shutoff, general points 

• Circuit 87M ON (Engine management ON)
• Engine runs
• Vehicle rolling
• Accelerator not operated
• Selector lever position "D" or "R" (with automatic transmission)
• Clutch pedal not actuated (with a manual transmission)
• Vehicle not in CC mode (with code MS1 (CC))
• Exhaust temperature in target area

Deceleration fuel shutoff, general 

The ME-SFI [ME] control unit (N3/34) performs a deceleration fuel shutoff dependent on the following sensors and signals:

• Coolant temperature sensor (B11/21), coolant temperature over direct line
• Accelerator pedal module (B37/4), accelerator pedal position over direct line
• Crankshaft Hall sensor (B70/2), engine rpm over direct line
• Clutch pedal switch (S40/3) and clutch pedal switch (S40/6) (with manual transmission), status of clutch pedal over direct line
• Fully integrated transmission control electric controller unit (VGS) (N15/11), gear range via the drive train CAN (CAN C) (with an automatic transmission)
• Electronic Stability Program control unit (N30/4), wheel speed via the chassis CAN (CAN E)

Deceleration fuel shutoff, function sequence 

In deceleration mode, the ME-SFI [ME] control unit switches off the fuel injectors (Y62) dependent on coolant temperature, engaged gear and engine speed, if the accelerator pedal is not actuated.

The fuel injectors (Y62) are switched on again when the accelerator pedal is operated.

The ME-SFI [ME] control unit (Y49/11) also adjusts the valve overlap to its minimum value through the intake camshaft solenoid (N3/34) and the exhaust camshaft solenoid (Y49/10). This ensures that an optimal conversion rate of the catalytic converter is more rapidly achieved.

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 reestablished after deceleration fuel shutoff, the ignition timing is briefly adjusted towards "retarded" by the ME-SFI [ME] control unit.

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 of the catalytic converter.