Starting System: Description and Operation

GF07.15-P-2001MCU Start Procedure, Function







1 Ignition/starter switch status
2 Fuel pump request
3 Fuel pump actuation
4 Air temperature in intake manifold
5 Indicator lamp request
6 Coolant temperature
7 Actuation of fuel injection valves
8 Ignition coils actuation
9 Starter actuation
10 Engine speed
A1 Instrument cluster
A1e26 "CHECK ENGINE" MIL
B11/4 Coolant temperature sensor
B28 Intake manifold pressure sensor
L5 Crankshaft position sensor
M1 Starter
M3/3 Fuel pump with fuel tank sensor
N3/10 ME-SFI [ME] control unit
N10/10 SAM control unit
S2/1 Ignition/starter switch
T1/1 Cylinder 1 ignition coil
T1/2 Cylinder 2 ignition coil
T1/3 Cylinder 3 ignition coil
Y62/1 Cylinder 1 fuel injection valve
Y62/2 Cylinder 2 fuel injection valve
Y62/3 Cylinder 3 fuel injection valve

CAN Controller Area Network (data bus/CAN bus) (CAN)

The start process includes the following partial functions:
^ Circuit 15 On
^ START
^ Start quantity control
^ Post-start enrichment

Circuit 15 ON
^ The SAM control unit checks drive authorization and applies an appropriate signal to the CAN.
^ The ME-SFI [ME] control unit requests the CHECK ENGINE indicator lamp in the instrument cluster to light up shortly.
^ The fuel pump with fuel level sensor is actuated via the SAM control unit for about 25 seconds.
This approach is particularly required after long periods of being switched off. This ensures that the fuel injection valves are supplied with sufficient fuel during starting. An engine start must be completed, however, before repeated actuation of the fuel pump with fuel level sensor.

Starting
The start function is activated by turning the transmitter key from position 1 (circuit 15 On) to position 2 (circuit 50 On) in the ignition/starter switch.
Actuation of the starter takes place directly by the SAM control unit.
The start process is ended again as soon as terminal 50 is no longer applied at the SAM control unit or the engine cranking speed is reached.

Start quantity control
As soon as the first rpm signal is recognized by the crankshaft position sensor during the start process, the SAM control unit energizes the fuel pump with fuel level sensor permanently. In order to facilitate starting of a cold engine, fuel is also injected during the starting procedure. The increase in injection quantity (start quantity) takes place depending on the coolant temperature and is achieved through extending the injection time.

The start quantity control is enabled after starter recognition and remains active until a stable idle speed is recognized by the ME-SFI [ME] control unit.
The higher the coolant temperature, the lower is the start quantity enable by the ME-SFI [ME] control unit.

Post-start enrichment
When the engine is cold, fuel precipitates on the walls of the intake manifold and is not available to the engine for combustion. The missing fuel volume is compensated by the post-start enrichment function.
After the cold start the fuel-air mixture is enriched for short time through longer injection times of the fuel injection valves. Post-start enrichment is achieved by the ME-SFI [ME] control unit and is dependent on the coolant temperature at engine start.