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 (engine management ON)
Engine running
On vehicles up to model year 2016, there is only one chassis CAN irrespective of the equipment installed.
On vehicles as of model year 2016, there are two chassis CAN variants depending on the equipment installed.
Variant 1
If the vehicle has none of the equipment codes named in variant 2, 2016 only one chassis CAN (CAN E) is present.
Variant 2
If the vehicle has one of the following equipment codes, there are two chassis CANs (chassis CAN 1 (CAN E1), chassis CAN 2 (CAN E2)):
Code 218 (Reversing camera)
Code 234 (Blind Spot Assist)
Code 459 (Steel suspension with adjustable damping)
Code 475 (Tire pressure monitor)
Code 476 (Lane Keeping Assist)
Code 513 (Speed Limit Assist)
CODE 614 (Bi-xenon headlamps)
CODE 615 (Bi-xenon headlamps with active curve lights)
CODE 618 (Bi-xenon headlamps)
Code 621 (Intelligent Light System (left-hand traffic))
CODE 622 (Intelligent Light System)
Code 631 (Static LED headlamps for left-hand traffic system)
Code 632 (Static LED headlamps for right-hand traffic system)
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)
Crankshaft Hall sensor (B70) (with rotational recognition), engine rpm
On-board electrical system battery voltage (G1) over "circuit 30"
Electronic ignition lock control unit(N73), "circuit 50 signal" via chassis CAN or via chassis CAN 1
Engine off time
When the ME-SFI [ME] control unit receives the "circuit 50 signal" from the electronic ignition lock control unit via chassis CAN or via chassis CAN 1 via chassis CAN 2, it increases the injection period of the fuel injectors for cylinders 1 to 4 (Y76/1 to 4). 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 post-start enrichment, the ME-SFI [ME] control unit computes the injection period based on the following sensors and signals:
Coolant temperature sensor, coolant temperature when starting
Combustion cycles after start
Fully integrated transmission control unit for dual clutch transmission (Y3/14n4) (for code (429) Dual clutch transmission), selector lever position via the drive train CAN (CAN C)
Correction programming using Xentry diagnostics
An additional fuel quantity is added to the engine by the ME-SFI [ME] control unit in line with the characteristics 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 warm-up enrichment, the ME-SFI [ME] control unit computes the injection period based on 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
An additional fuel quantity is added to the engine by the ME-SFI [ME] control unit in line with the characteristics 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 for cylinder 1 to 4 (T1/1 to 4) are determined in warm-up by its own 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 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.
Referenced documents
- gf0770p9998mt Overview of system components for gasoline injection and ignition system with direct injection
- gf0770p9998mta Overview of system components for gasoline injection and ignition system with direct injection
- gf0770p9998mtc Overview of system components for gasoline injection and ignition system with direct injection