Enrichment rate (A)-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 management ON)
Engine runs
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:
Starting mixture enrichment function sequence (t1)
Post-start enrichment function sequence (t2)
Warm-up enrichment function sequence (t3)
Starting mixture enrichment function sequence (t1)
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)
When it receives the circuit 50 signal from the electronic ignition lock control unit (EZS) (N3) via the chassis CAN (CAN E), the ME-SFI [ME] control unit (N73/34) extends the injection period of the fuel injectors (Y62).
The higher the coolant temperature, the shorter the injection period calculated by the ME-SFI [ME] control unit (N3/34).
The injection period is also dependent on the on-board electrical system voltage. In order to ensure that the start quantity is correct when the on-board electrical system voltage is low, the ME-SFI [ME] control unit (N3/34) increases the injection period.
No further engine start is possible below an on-board electrical system voltage of approx. 7 V.
Post-start enrichment function sequence (t2)
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 electric controller unit (VGS) (N15/11)
Correction programming using XENTRY diagnostics
An additional quantity of fuel is metered to the engine by the ME-SFI [ME] control unit (N334) in line with the characteristics map. To do this, the ME-SFI [ME] control unit (N3/34) extends the injection period for the fuel injectors (Y62).
Warm-up enrichment function sequence (t3)
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 using XENTRY diagnostics
An additional quantity of fuel is metered to the engine by the ME-SFI [ME] control unit (N334) in line with the characteristics map. To do this, the ME-SFI [ME] control unit (N3/34) extends the injection period for 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 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 period is mainly dependent on the coolant temperature at engine start.
Once enabled, the lambda control monitors the injection period.
Referenced documents
- gf0770s9998trc Overview of system components for gasoline injection and ignition system with direct injection