A | Enrichment rate |
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) |
P07.61-2691-01
Function requirements for starting, the post-start phase and warm-up enrichment, general points
Circuit 87M ON (Engine management ON)
The circuit relay 87M(F58kN) is switched on for circuit 15 ON.
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 start, post-start phase and warm-up enrichment function sequence function consists of the following partial functions:
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.
The ME-SFI [ME] control unit calculates the injection period for starting mixture enrichment on the basis of the following sensors and signals:
Electronic ignition lock control unit (N73), circuit 50
The status of circuit 50 is sent to the electronic ignition lock control unit via chassis CAN 1 (CAN E1), powertrain control unit (N127) and the drive train CAN (CAN ) to the ME-SFI [ME] control unit.
Coolant temperature sensor (B11/4), coolant temperature
Crankshaft Hall sensor (B70), engine rpm
On-board electrical system battery voltage (G1) through circuit 30
Engine off time
The ME-SFI [ME] control unit extends the actuation time of cylinder 1 to 8 fuel injectors (Y76/1 to Y76/8) and therefore the injection period.
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 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.
Calculation of the injection duration for post-start enrichment is calculated by the ME-SFI [ME] control unit on the basis of 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
The fully integrated transmission control unit sends the selector lever position via the drive train CAN to the ME-SFI [ME] control unit.
Correction programming over diagnosis
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
After the starting mixture enrichment and post-start enrichment, the fuel/ air mixture continues to be enriched via the warm-up enrichment. The warm-up enrichment compensates for fuel which condenses on the still cold cylinder barrel. Calculation of the injection duration for warm-up enrichment is calculated by the ME-SFI [ME] control unit on the basis of the following sensors and signals:
Left intake camshaft Hall sensor (B6/4) and right intake camshaft Hall sensor (B6/5), intake camshaft positions
Left exhaust camshaft Hall sensor (B6/6) and right exhaust camshaft Hall sensor (B6/7), exhaust camshaft positions
Coolant temperature sensor, coolant temperature
Left charge air temperature sensor (B1714) and right charge air temperature sensor (B17/15)
Pressure sensor downstream of left throttle valve (B28/22) and pressure sensor downstream of right throttle valve (B28/23), engine load
Crankshaft Hall sensor, engine speed
Correction programming over diagnosis
The engine is assigned an additional fuel quantity by the ME-SFI [ME] control unit according to a performance 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 (ignition coil for cylinders 1 + 2 up to ignition coil for cylinders 7 + 8 (T4 bis T4/3)) are determined in warm-up by a separate characteristics map.
The left intake camshaft solenoid (Y49/4), the right intake camshaft solenoid (Y49/5), the left exhaust camshaft solenoid (Y49/6) and the right exhaust camshaft solenoid (Y49/7) determine the exhaust gas recirculation rate through 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.
Referenced documents
- gf0770p9998mnf Overview of system components for gasoline injection and ignition system with direct injection