Function requirements, general
Engine runs
The ME-SFI [ME] control unit (N3/10) detects the engine running by evaluating the signals of the crankshaft Hall sensor (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
In order to achieve stable and smooth engine running for a cold start, the fuel/air mixture is enriched by the ME-SFI [ME] control unit.
Enrichment rate/time diagram |
a | Start |
b | Start of cutoff of post-start enrichment |
c | Start of warm-up enrichment |
t | Time |
t1 | Starting mixture enrichment (duration e.g. 2 s) |
t2 | Post-start enrichment (duration, e.g. 15 s at 15 °C coolant temperature) |
t3 | Warm-up enrichment (duration dependent on coolant temperature) |
A | Enrichment rate |
P07.61-2691-01
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) transmits the status of the on-board electrical system via the interior CAN (CAN B), the electronic ignition lock control unit (N73), the chassis FlexRay (Flex E), the powertrain control unit (N127) and the drive train CAN (CAN C1) to the ME-SFI [ME] control unit.
Status of circuit 50
The electronic ignition lock control unit transmits the status of circuit 50 via the chassis FlexRay, the powertrain control unit and the drive train CAN to the ME-SFI [ME] control unit.
The ME-SFI [ME] control unit calculates the required injection duration and 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)
Cylinder 5 fuel injector (Y76/5)
Cylinder 6 fuel injector (Y76/6)
Cylinder 7 fuel injector (Y76/7)
Cylinder 8 fuel injector (Y76/8)
The ME-SFI control unit () actuates the following components of the ignition system:
Cylinder 1+2 ignition coil (T4)
Cylinder 1 ignition coil (T4t1)
Cylinder 2 ignition coil (T4t2)
Cylinder 3+4 ignition coil (T4/1)
Cylinder 3 ignition coil (T4/1t3)
Cylinder 4 ignition coil (T4/1t4)
Cylinder 5+6 ignition coil (T4/2)
Cylinder 5 ignition coil (T4/2t5)
Cylinder 6 ignition coil (T4/2t6)
Cylinder 7+8 ignition coil (T4/3)
Cylinder 7 ignition coil (T4/3t7)
Cylinder 8 ignition coil (T4/3t8)
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 to ensure that the engine runs smoothly. The quantity of fuel condensing on the cold cylinder barrels is compensated by the post-start enrichment. To do this, the ME-SFI [ME] control unit extends the injection period of the fuel injectors.
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. To do this, the ME-SFI [ME] control unit extends the injection period of the fuel injectors.
The ME-SFI [ME] control unit calculates the injection duration for warm-up enrichment on the basis of the signals from the following sensors:
Left intake camshaft Hall sensor (B6/4)
Right intake camshaft Hall sensor (B6/5)
Left exhaust camshaft Hall sensor (B6/6)
Right exhaust camshaft Hall sensor (B6/7)
Coolant temperature sensor
Left charge air temperature sensor (B17/14)
Right charge air temperature sensor (B17/15)
Pressure sensor downstream of left throttle valve (B28/22)
Pressure sensor downstream of right throttle valve (B28/23)
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.
Referenced documents
- gf0770p9998mna Overview of system components for gasoline injection and ignition system with direct injection
- gf0770p9998mne Overview of system components for gasoline injection and ignition system with direct injection