Start, Post-Start Phase And Warm-Up Enrichment, Function - GF07.10-S-1007TRJ

Engine 274 in model 447.6/7 

with code XM0 (Facelift) 

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 ON (Engine management ON)
• Engine running.

Start phase, post-start phase and warm-up enrichment, general 

In order to achieve stable and smooth engine running for a cold start, the fuel/air mixture is enriched.

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.

Computation of the injection period for the starting mixture enrichment (t1) takes place over the ME-SFI [ME] control unit (N3/34) on the base of the following components and signals:

• Coolant temperature sensor (B11/21)
• Crankshaft Hall sensor (B70/2)
• On-board power supply voltage
• Electronic ignition lock control unit (EIS) (N73)

The ME-SFI [ME] control unit (N3/34) upon receipt of the signal "circuit 50" from the electronic ignition lock control unit (EZS) (N73) extends the injection duration of the fuel injectors (Y62).

The higher the coolant temperature, the shorter the injection duration calculated by the ME-SFI [ME] control unit.

The injection period is also dependent on the on-board electrical system voltage. To ensure the start quantity for a low on-board electrical system voltage, the MESFI [ME] control unit extends the injection duration.

An engine start is not possible under an on-board electrical system voltage of approx. 7 V.

Function sequence for post-start enrichment 

The leaning of the mixture by the fuel condensing on the cold cylinder walls is compensated for by the post-start enrichment (t2).

Computation of the injection period for the post-start enrichment (t2) takes place over the ME-SFI [ME] control unit (N3/34) on the base of the following components and signals:

• Coolant temperature sensor (B11/21)
• Combustion cycles after start
• Fully integrated transmission control (VGS) electric controller unit (N15/11) (Vehicles with code G42 (7G-TRONIC PLUS))
• Fully integrated transmission control (VGS) electric controller unit (N15/15) (Vehicles with code G43 (9G-TRONIC))
• Correction programming with XENTRY Diagnosis

An additional fuel quantity is added to the engine by the ME-SFI control unit in line with the characteristics map. The ME-SFI [ME] control unit extends for this purpose the injection duration of the fuel injectors (Y62).

Function sequence for warm-up enrichment 

In order to achieve a quicker warm-up, the fuel/air mixture is further enriched over the warm-up enrichment (t₃ ).

Computation of the injection period for the warm-up enrichment (t3) takes place over the ME-SFI [ME] control unit (N3/34) on the base of the following components and signals:

• Intake camshaft Hall sensor (B6/29)
• Exhaust camshaft Hall sensor (B6/30)
• Coolant temperature sensor (B11/21)
• Charge air temperature sensor upstream of throttle valve (B17)
• Charge air temperature sensor downstream of throttle valve (B17/16)
• Intake manifold pressure sensor (B28/24)
• Crankshaft Hall sensor (B70/2)
• Correction programming with XENTRY Diagnosis

An additional fuel quantity is added to the engine by the ME-SFI control unit in line with the characteristics map. The ME-SFI [ME] control unit extends for this purpose the injection duration of the fuel injectors (Y62).

The ignition angles of the ignition coils (T1) during warm-up are determined according to a specific characteristics map.

The intake camshaft solenoid (Y49/10) and the exhaust camshaft solenoid (Y49/11) determine the exhaust gas recirculation rate via 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.

Once enabled, the lambda control monitors the injection period.

Overview of system components for gasoline injection and ignition system with direct injection

GF07.70-S-9998TRJ