ME-SFI start, post-start phase and warm-up enrichment, function - GF07.61-P-3014MIS
ENGINE 272.9 in MODEL 221.0 /1 as of model year 2009/ AEJ 08
ENGINE 273.9 in MODEL 216.3, 221.0 /1 as of model year 2009/ AEJ 08
Enrichment rate/time diagram
Function requirements for starting, the post-start phase and warm-up enrichment
- Circuit 87M ON (engine control 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 start procedure.
For the starting mixture enrichment, the ME-SFI [ME] control unit calculates 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) through "circuit 30"
- EIS control unit (N73), circuit. 50 signal via the chassis CAN (CAN E)
- Engine off time
When it receives the "terminal 50 signal" from the EIS control unit over the chassis CAN, the ME-SFI [ME] control unit lengthens the injection time of the fuel injection valves (Y62).
Starting mixture enrichment remains active until the engine speed corresponding to 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 by the post-start enrichment.
The ME-SFI [ME] control unit calculates 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
- Electric controller unit (VGS) (Y3/8), selector lever position over the drive train CAN (CAN C)
- Correction programming with the Diagnosis Assistance System (DAS)
The ME-SFI [ME] control unit assigns an additional quantity of fuel to the engine depending on the performance 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 control compensates for fuel which precipitates on the still cold engine parts.
The ME-SFI [ME] control unit calculates the injection time for the warm-up enrichment using the following sensors and signals:
- Coolant temperature sensor
- Crankshaft Hall sensor, engine speed
- Hot film MAF sensor (B2/5), engine load
- Intake air temperature sensor (B2/5b1)
- LH and RH intake camshaft Hall sensors (B6/4, B6/5), intake camshaft positions
- LH and RH exhaust camshaft Hall sensors (B6/6, B6/7), exhaust camshaft positions
- Correction programming using DAS
The ME-SFI [ME] control unit assigns an additional quantity of fuel to the engine depending on the performance map.
To do this, the ME-SFI [ME] control unit extends the injection time of the fuel injection valves.
The ignition angles of the ignition coils (T1) during warm-up are determined according to a specific performance map.
The exhaust gas recirculation rate is determined by adjusting the valve overlap, using the LH and RH intake camshaft solenoids (Y49/4, Y49/5) and the LH and RH exhaust camshaft solenoids (Y49/6, Y49/7). 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 mainly depends on the coolant temperature at engine start.
On partial load, the crucial factor is engine load.
Once enabled, the lambda control monitors the injection time.
| Electrical function schematic for start phase, post-start phase and warm-up enrichment | Model 216 | PE07.61-P-2787-97CAB | ||
| Component description for ME-SFI [ME] control unit | N3/10 | Engine 273 | GF07.61-P-6000MLS | |