Smooth engine running analysis, function - GF07.10-P-1030G
ENGINE 273 in MODEL 463.202/222/236/237 up to 31.5.12 as of model year 2009/YoM 08
Function requirements for smooth engine running analysis, general points
- Circuit 87M ON (engine control ON)
- Engine running
Smooth engine running analysis, general points
Engine running is constantly monitored in order to protect the firewall catalytic converters from excessive thermal stresses if combustion misfires occur.
For smooth running evaluation, the ME-SFI [ME] control unit reads the following sensors and signals:
- Hot film MAF sensor, engine load
- LH and RH intake camshaft Hall sensor, intake camshaft positions
- LH and RH exhaust camshaft Hall sensor, exhaust camshaft positions
- Coolant temperature sensor
- Accelerator pedal sensor, accelerator pedal position
- Crankshaft Hall sensor, engine speed
- Instrument cluster, fuel level via the drive train CAN
- ESP control unit, wheel speed signal via the drive train CAN
Smooth engine running analysis function sequence
The function sequence is described in the following items:
- Combustion misfire detection function sequence
- Misfire counter function sequence
- Smooth running evaluation factors function sequence
Combustion misfire detection function sequence
For analyzing smooth engine running, the signal supplied by the crankshaft Hall sensor is analyzed using a sophisticated mathematical method to determine whether exact time synchronism exists between the individual combustions.
Each individual combustion must produce a characteristic acceleration at the increment wheel (perforated plate).
If there are combustion misfires, the increment wheel turns slightly more slowly until the next ignition (torque fluctuation).
If the smooth running evaluation in the ME-SFI [ME] control unit detects combustion misfiring, the corresponding fuel injection valve is no longer actuated after a certain number of combustion misfires. However, a maximum of two fuel injection valves may be deactivated simultaneously.
Misfire counter function sequence
The total number of combustion misfires detected is stored in the fault memory and broken down into:
- "Cylinder-specific" combustion misfires
- "Emission limit" combustion misfires
- "Catalytic converter damaging" combustion misfires
Smooth engine running signal
What is detected is combustion misfiring caused by:
- Ignition system
- Injection system
- Mechanical engine components (for example, valve seats, valve springs, unmetered air)
- Fuel deficiency
Smooth running evaluation factors function sequence
The following factors influence the smooth engine running analysis:
- Engine speed and engine load
- Coolant temperature
- Recognition of uneven road surface
- Synchronization of fuel injection and firing order
- Fuel reserve signal
- Sensor adaptation
Engine speed and engine load
Using the engine speed and engine load, the ME-SFI [ME] control unit calculates a reference value for the time between two combustions.
Coolant temperature
For a cold engine, more combustion misfires are permissible than for an engine at operating temperature.
Recognition of uneven road surface
Vibrations transmitted through the drive train may have a negative effect on engine running at certain engine speeds and load states. Therefore, the tolerance range for smooth running evaluation is increased on poor road surfaces ("wash board").
The ME-SFI [ME] control unit receives the wheel speed signal (for detection of uniform wheel speed) via the drive train CAN from the ESP control unit.
Synchronization of fuel injection and firing order
Cylinder identification is required for fault storage and evaluation, using the signals from the crankshaft Hall sensor and the intake camshaft Hall sensors or exhaust camshaft Hall sensors.
Fuel reserve signal
If combustion misfiring was detected, a fault is stored if the fuel level is too low. Combustion misfires due to fuel starvation are detected via this additional information.
The SAM rear evaluates the signals from the fuel level sensor, tank half left and right and issues an appropriate signal via the interior CAN to the instrument cluster.
The ME-SFI [ME] control unit receives the fuel level information from the instrument cluster via the drive train CAN.
Sensor adaptation
The tolerance range for smooth running evaluation is reduced after successful adaptation of the crankshaft Hall sensor.
In this way, the smooth running evaluation can be adapted to the specific smooth running characteristics of the engine.
The ME-SFI [ME] control unit stores the smooth operation characteristics of the engine During a deceleration phase accelerator pedal not operated) when uniform smooth operation is present. These are required as a comparison parameter for misfire detection.
The tolerance range for smooth running evaluation is preset in the ME-SFI [ME] control unit and can be adapted using the Diagnosis Assistance System (DAS) if necessary.
| Component description for ME-SFI [ME] control unit | N3/10 | GF07.61-P-6000G |