Overrun Mode Fuel Shutoff, Function - GF07.10-P-1014MMV
Engine 276.8 in model 205, 253
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
- Gear range "N" engaged (for a stationary or a rolling vehicle)
- Vehicle is not in cruise control mode
- Not too high an exhaust temperatures
The "Engine running" function requirements include all function sequences of the fuel low pressure and fuel high-pressure circuit, as described in the "Fuel supply" function.
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 dependent on the following sensors and signals:
- Coolant temperature sensor (B11/4)
- 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 deceleration mode, the ME-SFI [ME] control unit switches off the fuel injectors for cylinders to (Y76/1 to Y76/6) dependent on coolant temperature, engaged gear and engine speed, if 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 extending the injection time in order to protect the catalytic converters (three-way catalytic converters) from 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 (T11 to T16) 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.
| Electrical function schematic for deceleration fuel shutoff | PE07.10-P-2714-97FBB | ||
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-P-9998MMV |