Overrun Mode Fuel Shutoff, Function - GF07.10-P-1014MNB
Engine 178.9 In Model 190
Function requirements for deceleration fuel shutoff, general points
- Circuit 87M (engine management ON)
- Engine runs
- 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
- DKG control unit (N15/13), gear range via the drive train CAN (CAN C1)
- DISTRONIC electric controller unit (A89) (for code 239 (DISTRONIC PLUS)), increase/reduce engine torque request to adjust the target distance via drive train CAN, powertrain control unit (N127) and chassis CAN 1 (CAN E1)
- CC, increase/reduce engine torque request to adjust the target speed
Deceleration fuel shutoff, function sequence
The ME-SFI [ME] control unit switches off in decel mode the cylinder 1 to 8 (Y76/1 to Y76/8) fuel injectors dependent on the coolant temperature, the current gear range and the engine RPM if the following function requirements are fulfilled:
- Accelerator pedal not depressed.
- CC not placing an engine torque request.
- DISTRONIC PLUS not placing an engine torque request.
The fuel injectors are again switched-in if the accelerator pedal is actuated or the CC or DISTRONIC PLUS placing an engine torque request.
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 any sudden torque rise when combustion starts up again following deceleration fuel shutoff, the ME-SFI [ME] control unit adjusts the ignition angles of the ignition coils (ignition coil for cylinders 1 + 2 to ignition coil for cylinders 7 + 8 (T4 to T4/3)) briefly towards "retarded".
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-2714-97HBA | ||
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-P-9998MNB |