Start, Post-Start Phase And Warm-Up Enrichment, Function - GF07.10-D-1007TSB
Engine 274 in model 907
Block diagram
Enrichment rate/time diagram
Function requirements for starting, the post-start phase and warm-up enrichment, general points
- Circuit 87M (Engine management ON)
- Engine turning
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.
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 (N3/36) 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 duration (t1 ) based on the following signals:
- Coolant temperature sensor (B11/21)
- Crankshaft Hall sensor (B70/2), engine RPM
- Intake manifold pressure sensor (B28/24)
- On-board electrical system battery voltage (G1) over "circuit 30"
- Electronic ignition lock control unit (N73/8), signal "circuit 50" over chassis FlexRay (Flex E) to the drive train control unit (N127) and over the drive train CAN (CAN C)
- Engine off time
Upon receiving the "circuit 50" signal, the ME-SFI [ME] control unit extends the injection duration of the fuel injectors (Y62).
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 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 control unit extends the injection period.
Fuel condensing in the cold cylinder barrels is compensated for by the post-start enrichment (t2 ).
For post-start enrichment, the ME-SFI [ME] control unit computes the injection period based on the following signals:
- Coolant temperature sensor, coolant temperature at engine start
- Combustion cycles after start
- Fully integrated transmission control electric controller unit (VGS) (N15/15) (with code G43 (9G-TRONIC automatic transmission), selector lever position via the drive train CAN
- Correction programming using XENTRY diagnostics
An additional fuel quantity is added to the engine by the ME-SFI control unit in line with the characteristics map. To do this, the ME-SFI control unit extends the injection period of the fuel injectors.
Function sequence for warm-up enrichment
After start and post-start enrichment, the fuel/air mixture undergoes further enrichment by means of warm-up enrichment (3). 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 (B6/29)
- Exhaust camshaft Hall sensor (B6/30)
- Coolant temperature sensor (B11/21)
- Charge air temperature sensor upstream of throttle valve (B17)
- Charge air temperature sensor downstream of throttle valve (B17/16)
- Crankshaft Hall sensor (B70/2), engine RPM
- Correction programming using XENTRY diagnostics
An additional fuel quantity is added to the engine by the ME-SFI control unit in line with the characteristics map. To do this, the ME-SFI control unit extends the injection period of the fuel injectors.
The ignition angles of the ignition coils (T1) during warm-up are determined according to a specific characteristics map.
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-D-2707-97TSA |
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-D-9998TSB |