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

GF07.10-P-1007MI

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

04.12.2012

ENGINE	272.9 (except 272.982) in MODEL 204.0/2
	as of model year 2009
ENGINE	272.9 (except 272.983) in MODEL 212
ENGINE	272.9 (except 272.984) in MODEL 207
ENGINE	272.9 in MODEL 204.9
ENGINE	273.9 in MODEL 207, 212

Enrichment rate/time diagram

a	Start
b	Start of cutoff of post-start enrichment
c	Start of warm-up enrichment
t	Time
t1	Starting mixture enrichment (duration e.g. 2 s)
t2	Post-start enrichment (duration e.g. 15 seconds at coolant temperature of 15°C)
t3	Warm-up enrichment (duration dependent on coolant temperature)
A	Enrichment rate

P07.61-2691-01

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

 Circuit 87M ON (engine timing 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 (N310) 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 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) via "circuit 30"

- electronic ignition lock control unit (N73), "circuit 50 signal" via the chassis CAN (CAN E)

– engine shutoff time

When it receives the "circuit 50 signal" from the electronic ignition lock control unit over the chassis CAN, the ME-SFI [ME] control unit extends the injection time of the injection valves (Y62).

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 time calculated by the ME-SFI [ME] control unit.

The injection time is 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 time.

 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 for by the post-start enrichment.

The ME-SFI [ME] control unit computes 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

- fully integrated transmission control controller unit (Y3/8), selector lever position via the drive train CAN (CAN C) (for an automatic transmission)

- correction programming with the Diagnosis Assistance System (DAS)

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 time of the injection valves.

Function sequence for warm-up enrichment

After start and post-start enrichment, the fuel-air mixture is further enriched by the warm-up enrichment. The warm-up enrichment compensates for fuel which precipitates on the still cold cylinder barrel.

The ME-SFI [ME] control unit computes the injection time for the warm-up enrichment using the following sensors and signals:

– hot film MAF sensor (B2/5), engine load

- intake air temperature sensor (B25b1)

– left and right intake camshaft Hall sensor (B6/4, B6/5), intake camshaft positions

– left and right exhaust camshaft Hall sensor (B6/6, B6/7), exhaust camshaft positions

- coolant temperature sensor

– crankshaft Hall sensor, engine speed

- correction programming using DAS

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 time of the injection valves.

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 time 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 time.

	Electrical function schematic for start phase, post-start phase and warm-up enrichment	MODEL 204	PE07.10-P-2707-97FAB
		MODEL 207	PE07.10-P-2707-97EAB
		MODEL 212	PE07.10-P-2707-97DAB
	Table of contents for function description of motor electronics (ME-SFI) fuel injection and ignition system		GF07.61-P-0999MI