Start, Post-Start Phase And Warm-Up Enrichment, Function - GF07.10-P-1007MRA
Engine 274.9 in model 205 (except 205.047/053/054/147/247/253)
Engine 274.9 in model 253 (except 253.354/954)
Enrichment rate/time diagram
Function requirements for starting, the post-start phase and warm-up enrichment, general points
- Circuit 87M (Engine management ON)
- Engine running
Start phase, post-start phase and warm-up enrichment, general
To ensure stable and smooth engine running during a cold start, the ME-SFI [ME] control unit (N3/10) enriches the fuel/air mixture. Function sequence for start phase, post-start phase and warm-up enrichment
The function sequence is divided into the following subfunctions:
- Function sequence for starting mixture enrichment
- Function sequence for post-start enrichment
- Function sequence for warm-up enrichment
Function sequence for starting mixture enrichment
To allow easier starting when the engine is cold, more fuel has to be injected during the starting procedure.
For the starting mixture enrichment, the ME-SFI [ME] control unit computes the injection period based on the following signals:
- Coolant temperature sensor (B11/4)
- Crankshaft Hall sensor (B70), engine RPM
- On-board electrical system battery voltage (G1) over "circuit 30"
- Electronic ignition lock control unit (N73), "Circuit 50 signal" via the chassis FlexRay (Flex E) to the powertrain control unit (N127) and via the drive train CAN (CAN C1)
- Engine off time
When it receives the "circuit 50 signal" from the electronic ignition lock control unit over the suspension FlexRay, powertrain control unit and the drive train CAN, the ME-SFI [ME] control unit extends the injection period of the cylinder 1 fuel injectors to cylinder 4 fuel injectors (Y76/1 to Y76/4).
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 period calculated by the ME-SFI [ME] control unit.
The injection period is also dependent on the battery voltage. In order to guarantee the start quantity for a lower battery voltage, the ME-SFI [ME] control unit extends the injection period.
No further engine start is possible below an battery voltage of approx. 7 V.
Function sequence for post-start enrichment
After a cold start the fuel/air mixture is enriched for a short time to ensure that the engine runs smoothly.
Fuel condensing in the cold cylinder barrels is compensated for by the post-start enrichment.
For post-start enrichment, the ME-SFI [ME] control unit computes the injection period based on the following signals:
- Coolant temperature sensor, coolant temperature when starting
- Combustion cycles after start
- Fully integrated transmission control unit (Y3/8n4), selector lever position via the drive train CAN (for an A/T)
- Correction programming using XENTRY diagnostics
An additional fuel quantity is added to the engine by the ME-SFI [ME] control unit in line with the characteristics map.
To do this, the ME-SFI [ME] control unit extends the injection period of the fuel injectors.
Function sequence for warm-up enrichment
Following start and post-start enrichment, the fuel/air mixture undergoes further enrichment by means of warm-up enrichment. The warm-up enrichment compensates for fuel which condenses on the still cold cylinder barrel.
For warm-up enrichment, the ME-SFI [ME] control unit computes the injection period based on the following signals:
- intake camshaft Hall sensor (B6/15), intake camshaft setting
- Exhaust camshaft Hall sensor (B6/16), exhaust camshaft setting
- Coolant temperature sensor
- Charge air temperature sensor upstream of throttle valve (B17/7)
- Charge air temperature sensor downstream of throttle valve (B17/9)
- Pressure sensor downstream of throttle valve (B28/7), engine load
- Crankshaft Hall sensor, engine speed
- Correction programming using XENTRY diagnostics
An additional fuel quantity is added to the engine by the ME-SFI [ME] control unit in line with the characteristics map. To do this, the ME-SFI [ME] control unit extends the injection period of the fuel injectors.
The ignition angles of the ignition coils for cylinder 1 ignition coil through to cylinder 4 ignition coil (T1/1 to T1/4) are determined in warm-up by its own characteristics map.
The intake camshaft solenoid (Y49/1) and the exhaust camshaft solenoid (Y49/2) determine the exhaust gas recirculation rate by means of the valve overlap. As the hot exhaust gases heat up the combustion chambers, fuel evaporation is increased and fuel enrichment can be reduced.
In the idle speed range, injection period is mainly dependent on the coolant temperature at engine start.
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-2707-97FBA | ||
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-P-9998MRA |