GF07.10-P-1007MAW Start, Post-Start Phase and Warm-Up Enrichment, Function
GF07.10-P-1007MAW Start, Post-start Phase and Warm-up Enrichment, Function
ENGINES 156.9 in MODEL 204.0 /2 /3, 212.0 /2
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 seconds at coolant temperature of 15°C)
t3 Warm-up enrichment (duration dependent on coolant temperature)
A Enrichment rate
Function requirements for starting, the post-start phase and warm-up enrichment, general points
^ Circuit 87M (engine timing 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 time using the following sensors and signals:
- Coolant temperature sensor (B11/4)
- Crankshaft Hall sensor (B70), engine speed
- On-board electrical system battery voltage (G1) over "circuit 30"
- Electronic ignition lock control unit (N73), "circuit 50 signal" via the chassis CAN (CAN E)
- Engine off time
When it receives the "circuit 50 signal" from the electronic ignition lock control unit over the chassis CAN, the ME-SFI [ME] control unit extends the injection time of the injection valves (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 is the injection time calculated by the ME-SFI [ME] control unit.
The injection times are also dependent on the battery voltage. In order to guarantee the start quantity for a low battery voltage, the ME-SFI [ME] control unit extends the injection times.
No further engine start is possible below an engine start 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.
The ME-SFI [ME] control unit computes the injection time for the post-start enrichment according to the following sensors and signals:
- Coolant temperature sensor, coolant temperature at engine start
- Combustion cycles after start
- Fully integrated transmission controller unit (Y3/8), selector lever position via the drive train CAN (CAN C)
- Correction programming using Xentry diagnostics
The ME-SFI [ME] control unit allocates an additional fuel quantity to the engine depending on the characteristics map.
To do this, the ME-SFI [ME] control unit extends the injection time of the injection valves.
Function sequence for warm-up enrichment
After the 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 precipitates on the still cold cylinder barrel.
The ME-SFI [ME] control unit computes the injection time for the warm-up enrichment using the following sensors and signals:
- LH and RH hot film MAF sensor (B2/6, B2/7), engine load
- LH and RH intake camshaft Hall sensor (B6/4, B6/5), intake camshaft positions
- LH and RH exhaust camshaft Hall sensor (B6/6, B6/7), exhaust camshaft positions
- Coolant temperature sensor
- Intake air temperature sensor (B17)
- Crankshaft Hall sensor, engine speed
- Correction programming using Xentry diagnostics
The ME-SFI [ME] control unit allocates an additional fuel quantity to the engine depending on the characteristics map.
To do this, the ME-SFI [ME] control unit extends the injection time of the injection valves.
The ignition angles of the ignition coils (T1) during warm-up are determined according to a specific characteristics map.
The LH and RH intake camshaft solenoids (Y49/4, Y49/5) and the LH and RH exhaust camshaft solenoids (Y49/6, Y49/7) determine the valve overlap via the exhaust gas recirculation rate. 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 time is mainly dependent on the coolant temperature at engine start.
On partial load, the crucial factor is the engine load.
Once enabled, the lambda control monitors the injection time.
