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

P07.61-2691-01

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

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

 Circuit 87M (engine control 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.

For an engine start below -15°C switching takes place for a short time into gasoline operation.

Gasoline operation is maintained until various temperature-dependent parameter values have been reached.

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In order to achieve the parameter values, the ME-SFI [ME] control unit extends the injection time of the fuel injectors (Y76). Only then can gas operation be selected.

During changeover into gas operation the ME-SFI [ME] control unit actuates the gas injection valves gas (Y106) over the CNG control unit (N118/2).

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

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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) (with direction of rotation recognition), motor rpm

- On-board electrical system battery voltage (G1) over "circuit 30"

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

- Engine off time

When it receives the "circuit 50 signal" from the electronic ignition lock control unit via the chassis CAN, the ME-SFI [ME] control unit extends the injection time of the fuel injectors.

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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.

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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 when starting

- Combustion cycles after start

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- Fully integrated transmission control unit for dual clutch transmission (Y3/14n4), selector lever position via the drive train CAN (CAN C)

- Correction programming using Xentry diagnostics

The ME-SFI [ME] control unit allocates an additional fuel quantity to the engine depending on the characteristics map.

To do this, the ME-SFI [ME] control unit extends the injection time of the fuel injectors.

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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:

- intake camshaft Hall sensor (B6/15), intake camshaft setting

- exhaust camshaft Hall sensor (B6/16), exhaust camshaft setting

- Coolant temperature sensor

- Charge air temperature sensor upstream of throttle valve (B17/7)

- Charge air temperature sensor downstream of throttle valve (B17/9)

- Pressure sensor downstream of throttle valve (B28/7), engine load

- Crankshaft Hall sensor (with direction of rotation recognition), engine rpm

- Correction programming using Xentry diagnostics

The ME-SFI [ME] control unit allocates an additional fuel quantity to the engine depending on the characteristics map.

To do this, the ME-SFI [ME] control unit extends the injection time of the fuel injectors.

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

The intake camshaft solenoid (Y49/1) and the exhaust camshaft solenoid (Y49/2) determine the exhaust gas recirculation rate by means of 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.