Overrun Mode Fuel Shutoff, Function - GF07.10-D-1014TSB
Engine 274 in model 907
Block diagram
Function requirements for deceleration fuel shutoff, general points
- Circuit 87M (Engine management ON)
- Engine running.
- Accelerator not operated
- Drive range "D" or "R" engaged (with automatic transmission)
- 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.
- reducing fuel consumption.
- improving exhaust characteristics.
The ME-SFI [ME] control unit (N3/36) realizes an overrun mode fuel shutoff depending on the following signals:
- Coolant temperature sensor (B11/21)
- Crankshaft Hall sensor (B70/2), engine RPM
- Accelerator pedal module (A68), accelerator pedal position via powertrain control unit (N127) and drive CAN (CAN C)
- Clutch travel sensor (B109) (manual transmission with code MJ8 (ECO start/stop function)), via powertrain control unit and drive CAN
- Clutch pedal switch (manual transmission without code MJ8 (ECO start/stop function)), via powertrain control unit and drive CAN
- Clutch pedal switch UP (manual transmission without code MJ8 (ECO start/stop function)), via powertrain control unit and drive CAN
- Fully integrated transmission control (VGS) electric controller unit (N15/15), drive range via the drive CAN (with automatic transmission)
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 are switched on again when the accelerator pedal is operated.
If the clutch pedal is actuated for a manual transmission the deceleration fuel shutoff is broken off or suppressed.
The ME-SFI [ME] control unit also adjusts the camshafts to a position with reduced valve overlap via the intake camshaft adjustment solenoid (Y49/10) and the exhaust camshaft adjustment solenoid (Y49/11). 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 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 (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 of the catalytic converter.
| Electrical function schematic for deceleration fuel shutoff | PE07.10-D-2714-97TSB |
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-D-9998TSB |