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

Engine 274.9 in model 205 (except 205.047/053/054/147/247/253) 

Engine 274.9 in model 253 (except 253.354/954) 

Function requirements for deceleration fuel shutoff, general points 

• Circuit 87M (Engine management ON)
• Engine runs
• Accelerator not operated
• Gear range "D" or "R" (with automatic transmission), 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

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)
• Accelerator pedal sensor (B37), accelerator pedal position
• Clutch pedal sensor (B53/1) (with manual transmission)
• Crankshaft Hall sensor (B70), engine RPM
• Fully integrated transmission control unit (Y3/8n4), gear range via drive train CAN (CAN C1) (for A/T)

Deceleration fuel shutoff, function sequence 

In decel mode the ME-SFI [ME] control unit switches off cylinder 1 injection nozzle to cylinder 4 injection nozzle (Y76/1 to Y76/4) dependent on the coolant temperature, the engaged gear and the engine RPM, if the accelerator pedal is not depressed.

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 uses the intake camshaft solenoid (Y49/1) and the exhaust camshaft solenoid (Y49/2) to adjust the camshafts into 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 for cylinders 1 to ignition coil for cylinders 4 (T1/1 to T1/4)) 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 of the catalytic converter.

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