Start, Post-Start Phase And Warm-Up Enrichment, Function - GF07.10-P-1007MNH
Engine 176.9, 177.9 in model 463
as of model year 2019
Enrichment rate/time diagram
Function requirements for starting, the post-start phase and warm-up enrichment, general points
- Circuit 87M (Engine management ON)
- Engine runs
Start phase, post-start phase and warm-up enrichment, general
To ensure stable and smooth engine running during a cold start, the ME-SFI 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 control unit computes the injection period based on the following sensors and signals:
- Coolant temperature sensor (B11/4), coolant temperature
- 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 chassis FlexRay (Flex E), powertrain control unit (N127) and drive CAN (CAN C1)
- Engine off time
Upon receiving the "Circuit 50 signal" from the electronic ignition lock control unit via chassis FlexRay, powertrain control unit and drive CAN, the ME-SFI control unit extends the injection duration for the fuel injectors for cylinder 1 to 8 (Y76/1 to Y76/8).
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.
o further engine start is possible below a 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 the starting mixture enrichment, the ME-SFI control unit computes the injection period for the post-start enrichment using the following sensors and signals:
- Coolant temperature sensor, coolant temperature when starting
- Combustion cycles after start
- Fully integrated transmission control unit (Y3/8n4), selector lever position over the drive CAN (CAN C)
- 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 is further enriched by the warm-up enrichment. The warm-up enrichment compensates for fuel which condenses on the still cold cylinder barrel. For the starting mixture enrichment, the ME-SFI control unit computes the injection period for warm-up enrichment using the following sensors and signals:
- Left and right intake camshaft hall sensors (B6/4, B6/5), intake camshaft positions
- Left and right exhaust camshaft hall sensors (B6/6, B6/7), exhaust camshaft positions
- Coolant temperature sensor, coolant temperature
- Left and right charge air temperature sensor (B17/14, B17/15)
- Pressure sensor downstream of left and right throttle valve (B28/22, B28/23), 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 control unit in line with the characteristics map. To do so, the ME-SFI control unit extends the injection period for the fuel injectors for cylinders 1 to 8. The ignition angles of the ignition coils for cylinder 1 + 2 to cylinder 7 + 8 (T4 to T4/3) are determined in warm-up by an own characteristics map.
The left and right intake camshaft solenoids (Y49/4, Y49/5) and the left and right exhaust camshaft solenoids (Y496, Y497) determine the exhaust gas recirculation rate due to 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-2707-97ZGF | ||
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-P-9998MNH |