Smooth engine running analysis, function - GF07.10-P-1030MOS
ENGINE 275.953 in MODEL 216.376, 221.176 as of model year 2009 /AEJ 08
ENGINE 275.982 in MODEL 216.379, 221.179 as of model year 2009 /AEJ 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 (N3/10) reads the following sensors and signals:
- Camshaft Hall sensor, right cylinder bank (B6/3)
- Coolant temperature sensor ()B11/4
- Charge air temperature sensor (B17/8) and pressure sensor downstream of throttle valve actuator (B28/7), engine load
- Accelerator pedal sensor (B37), accelerator pedal position
- Crankshaft position sensor (L5), engine speed
- Instrument cluster (A1), fuel level via the chassis CAN (CAN E)
- ESP control unit (N47-5), wheel speed signal via the chassis CAN
Smooth engine running analysis function sequence
The function sequence is described in the following steps:
- Function sequence for combustion misfire detection
- Function sequence for misfire counter
- Function sequence factors for smooth running evaluation
Function sequence for combustion misfire detection
For analyzing smooth engine running, the signal supplied by the crankshaft position 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 (Y62) is no longer actuated after a certain number of combustion misfires. However, a maximum of two fuel injection valves may be deactivated simultaneously.
Function sequence for misfire counter
The total number of combustion misfires detected is stored in the fault memory and subdivided 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
Function sequence factors for smooth running evaluation
The following factors affect the smooth running evaluation:
- Engine speed and engine load
- Coolant temperature
- Recognition of an 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 an 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 chassis CAN from the ESP control unit.
Synchronization of fuel injection and firing order
Cylinder detection using the signals from the crankshaft position sensor and camshaft Hall sensor on the RH cylinder bank is required for fault storage and assessment.
Fuel reserve signal
If combustion misfiring has been 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 rear SAM control unit with fuse and relay module (N10/2) evaluates the signals from the fuel level indicator sensors of the LH and RH tank halves (B4/1, B4/2) and sends the corresponding CAN signal via the interior CAN (CAN B) to the instrument cluster. The ME-SFI [ME] control unit receives the fuel level information from the instrument cluster via the chassis CAN.
Sensor adaptation
The tolerance range for smooth running evaluation is reduced after successful adaptation of the crankshaft position 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.
| Electrical function schematic for smooth running evaluation ME | Model 216 Model 221 |
PE07.61-P-2770-97CAA PE07.61-P-2770-97SAA |
|
| Component description for ME-SFI [ME] control unit | N3/10 | GF07.61-P-6000MOS |