Start, post-start phase and warm-up enrichment, function - GF07.10-P-1007MMS

ENGINE 157.9 in MODEL 212, 218 as of model year 2014 

ENGINE 278.9 in MODEL 207, 212, 218 as of model year 2014 

Enrichment rate/time diagram 

Fig 1: Engine Enrichment Rate/Time Graph

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 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 period based on the following sensors and signals:

• Coolant temperature sensor (B11/4) (model 207, 212), coolant temperature sensor (B11/4) (model 218)
• 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)
• Engine off time

When it receives the "circuit 50 signal" from the electronic ignition lock control unit via chassis CAN 1, the ME-SFI [ME] control unit increases the injection duration 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 starting mixture enrichment, the ME-SFI [ME] control unit computes the injection period for the post-start enrichment using the following sensors and signals:

• Coolant temperature sensor, coolant temperature when starting
• Combustion cycles after start
• Fully integrated transmission controller unit (Y38), selector lever position via the drivetrain CAN (CAN C)
• 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 performance map. To do this, the ME-SFI [ME] control unit extends the injection period of the fuel injectors.

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
• Charge air temperature sensor (B17/8)
• Pressure sensor downstream of throttle valve (B28/7), 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 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 (T1) during warm-up are determined according to a specific 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.