Start, Post-Start Phase And Warm-Up Enrichment, Function - GF07.10-P-1007MNB

Engine 178.9 In Model 190

Enrichment rate/time diagram

Courtesy of MERCEDES-BENZ USA

Function requirements for starting, the post-start phase and warm-up enrichment, general points

Circuit 87M (engine management ON)
Engine runs

The " Engine running" function requirements include all function sequences of the fuel low pressure and fuel high-pressure circuit, as described in the "Fuel supply" function.

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 period based on the following sensors and signals:

Coolant temperature sensor (B11/4), coolant temperature
Crankshaft Hall sensor (B70), engine RPM
On-board electrical system battery voltage (G1) over "circuit 30"
Electronic ignition lock control unit (N73), "Circuit 50 signal" via chassis CAN 1 (CAN E1), powertrain control unit (N127), and drive train CAN (CAN C1)
Engine off time

Upon receiving the "circuit 50 signal", the ME-SFI [ME] control unit extends the injection period of the fuel injectors (Y76).

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 an 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.

For the post-start enrichment, the ME-SFI [ME] control unit computes the injection period based on the following sensors and signals:

Coolant temperature sensor, coolant temperature when starting
Combustion cycles after start
DKG control unit (N15/13), selector lever position via drive train CAN
Correction programming using Xentry diagnostics

Function sequence for warm-up enrichment

Following start and post-start enrichment, the fuel/air mixture undergoes further enrichment by means of warm-up enrichment. The warm-up enrichment compensates for fuel which condenses on the still cold cylinder barrel. For the starting mixture enrichment, the ME-SFI [ME] control unit computes the injection period for warm-up enrichment using the following sensors and signals:

Left and right intake camshaft hall sensors (B6/4, B6/5), intake camshaft positions
Left and right exhaust camshaft hall sensors (B6/6, B6/7), exhaust camshaft positions
Coolant temperature sensor, coolant temperature
Left and right charge air temperature sensors (B17/14, B17/15), charge air temperature
Left and right pressure sensors downstream throttle valve (B28/22, B28/23), engine load
Crankshaft Hall sensor, engine speed
Correction programming using Xentry diagnostics

An additional quantity of fuel 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. The ignition angles of the ignition coils (ignition coils for cylinder 1 + 2 through to ignition coils for cylinder 7 + 8 (T4 - T4/3) are determined in warm-up by an own characteristics map.

The left and right intake camshaft solenoids (Y49/4, Y49/5) and the left and right exhaust camshaft solenoids (Y496, Y497) determine the exhaust gas recirculation rate due to 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.