Overrun Mode Fuel Shutoff, Function - GF07.10-P-1014MRS

Engine 264.9 in Model 205, 253 

Function requirements, general 

• Engine runs
• Vehicle rolls without load request
• Not too high an exhaust temperatures

The ME-SFI [ME] control unit (N3/10) detects the Engine running via the evaluation of the crankshaft Hall sensor signals (B70). The ME-SFI [ME] control unit directly reads in the signals of the crankshaft Hall sensor.

The fully integrated transmission control unit (Y3/8n4) transmits information on the engaged drive range via the drive CAN (CAN C1) to 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 the catalytic converters.

Inertia fuel shutoff 

The overrun mode fuel shutoff is a deliberate, temporary interruption of the fuel supply, if no output is required. The overrun mode fuel shutoff basically serves for fuel economy. In the case of an active overrun mode fuel shutoff, the Engine drag torque is used to decelerate the vehicle. The overrun mode fuel shutoff is active above the idle speed.

The ME-SFI [ME] control unit evaluates the following signals for the implementation of the overrun mode fuel shutoff:

• Coolant temperature

  Coolant temperature sensor (B11/4)

• Accelerator pedal position

  The powertrain control unit (N127) directly reads in the signals of the accelerator pedal sensor (B37) and transmits the accelerator pedal position via the drive CAN to the ME-SFI [ME] control unit.

• Engine speed

  Crankshaft Hall sensor

• Drive position

The ME-SFI [ME] control unit stops injection by no longer actuating the following components:

• Cylinder 1 fuel injector (Y76/1)
• Cylinder 2 fuel injector (Y76/2)
• Cylinder 3 fuel injector (Y76/3)
• Cylinder 4 fuel injector (Y76/4)

The fuel injectors are switched on again if the accelerator pedal is actuated or an Engine torque request is pending.

After the overrun mode fuel shutoff, the ME-SFI [ME] control unit briefly enriches the fuel/air mixture in order to free the catalytic converters from enriched oxygen.

In order to prevent the Engine torque from increasing abruptly when combustion resumes after the deceleration fuel shutoff, the ME-SFI [ME] control unit adjusts the ignition in the "retarded" direction.

The ME-SFI [ME] control unit actuates the following components for this purpose:

• Cylinder 1 ignition coil (T1/1)
• Cylinder 2 ignition coil (T1/2)
• Cylinder 3 ignition coil (T1/3)
• Cylinder 4 ignition coil (T1/4)

The camshafts are adjusted to a position with reduced valve overlap so that a reliable combustion without misfires can take place. The ME-SFI [ME] control unit directly actuates the intake camshaft adjustment solenoid (Y49/1) and the exhaust camshaft adjustment solenoid (Y49/2).

	Electrical function schematic for deceleration fuel shutoff		PE07.10-P-2714-97FBI
	Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-P-9998MRS