Start, Post-Start Phase And Warm-Up Enrichment, Function - GF07.10-P-1007MRD

Engine 274.9 in model 213, 238 

up to model year 2021 

Function requirements, general 

• Engine runs

The ME-SFI [ME] control unit (N3/10) detects 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.

Start phase, post-start phase and warm-up enrichment, general 

The ME-SFI [ME] control unit enriches the fuel/air mixture in order to achieve stable and smooth engine running in the case of a cold start.

Enrichment rate/time diagram a b c t t1 

Courtesy of MERCEDES-BENZ USA

Starting mixture enrichment 

To allow easier starting when the engine is cold, more fuel has to be injected during the starting procedure.

The ME-SFI [ME] control unit calculates the injection duration for starting mixture enrichment on the basis of the signals from the following sensors:

• Coolant temperature sensor (B11/4)
• Crankshaft Hall sensor

The ME-SFI [ME] control unit extends the injection duration for starting mixture enrichment dependent on the following variables:

• Engine off time
• On-board power supply voltage

  The front SAM control unit (N10/6) sends information on the on-board electrical system utilization via the interior CAN (CAN B), electronic ignition lock control unit (N73), suspension FlexRay (Flex E), powertrain control unit (N127) and drive CAN (CAN C1) to the ME-SFI [ME] control unit.

• Status of circuit 50

The electronic ignition lock control unit transmits the circuit 50 status via the suspension FlexRay, powertrain control unit and drive CAN to the ME-SFI [ME] control unit.

The ME-SFI [ME] control unit calculates the required injection duration and accordingly actuates the following components of the fuel injection system:

• 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 ME-SFI [ME] control unit actuates the following ignition system components:

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

Starting mixture enrichment remains active until the engine speed dependent on the particular coolant temperature is exceeded. The higher the coolant temperature, the shorter the injection duration calculated by the ME-SFI [ME] control unit.

No engine start is possible below an on-board electrical system voltage of approx. 7 V.

Post-start enrichment 

After a cold start, the fuel/air mixture is enriched for a short time so that the engine runs smoothly. The quantity of fuel condensing on the cold cylinder barrels is compensated by the post-start enrichment. The ME-SFI [ME] control unit extends the injection duration for this purpose.

The ME-SFI [ME] control unit calculates the injection duration on the basis of the signals from the coolant temperature sensor. In addition, the ME-SFI [ME] control unit evaluates the combustion cycles after the start, and the transmission selector lever position. The fully integrated transmission control unit (Y3/8n4) sends information on the gear range engaged via the drive train CAN to the ME-SFI [ME] control unit.

Warm-up enrichment 

Following start and post-start enrichment, the fuel/air mixture undergoes further enrichment by means of warm-up enrichment. The quantity of fuel condensing on the still cold cylinder barrels is compensated by the warm-up enrichment. The ME-SFI [ME] control unit extends the injection duration for this purpose.

The ME-SFI [ME] control unit calculates the injection duration for warm-up enrichment on the basis of the signals from the following sensors:

• Intake camshaft Hall sensor (B6/15)
• Exhaust camshaft Hall sensor (B6/16)
• Coolant temperature sensor
• Pressure sensor downstream of throttle valve (B28/7)
• Crankshaft Hall sensor

The exhaust gas recirculation is activated while still in the warm-up phase. The hot exhaust provides additional heating of the combustion chambers. This improves the fuel evaporation and the warm-up enrichment can be reduced.

In neutral, the injection duration is primarily dependent on the coolant temperature when the engine starts. For partial load, the crucial factor is the engine load. Once enabled, the lambda control monitors the injection period.

	Electrical function schematic for start phase, post-start phase and warm-up enrichment		PE07.10-P-2707-97DBD
	Overview of system components for gasoline injection and ignition system with direct injection	Engine 274.9 in model 213 (except 213.050/053/153), 238 up to model year 2021	GF07.70-P-9998MRD
		Engine 274.9 in model 213.050/053/153 up to model year 2021	GF07.70-P-9998MRP