Start, Post-Start Phase And Warm-Up Enrichment, Function - GF07.10-P-1007MRS
Engine 264.9 in model 205, 253
Enrichment rate/time diagram
Starting mixture enrichment
To allow easier starting when the Engine is cold, more fuel has to be injected during the starting procedure.
The electronic ignition lock control unit (N73) transmits the status of circuit 50 via chassis FlexRay (Flex E), the powertrain control unit (N127) and the drive train CAN (CAN C1) to the ME-SFI [ME] control unit.
The ME-SFI control unit calculates the injection duration for starting mixture enrichment based on the following signals:
- Coolant temperature
Coolant temperature sensor (B11/4)
- Engine speed
Crankshaft Hall sensor (B70)
The ME-SFI [ME] control unit additionally extends the injection duration for starting mixture enrichment depending on the Engine off time.
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)
Start phase, post-start phase and warm-up enrichment, general
To achieve stable and smooth Engine running during a cold start, the ME-SFI control unit (N3/10) enriches the fuel/air mixture.
- 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.
Post-start enrichment
After a cold start, the fuel/air mixture is enriched for a short time to stabilize Engine running. 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 control unit calculates the injection duration for warm-up enrichment based on the following signals:
- Intake camshaft position
Intake camshaft Hall sensor (B6/15)
- Exhaust camshaft position
Exhaust camshaft Hall sensor (B6/16)
- Coolant temperature
Coolant temperature sensor
- Engine load
Pressure and temperature sensor downstream of throttle valve (B28/27)
- Engine speed
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-2707-97FBI | ||
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-P-9998MRS |