Smooth engine running analysis, function - GF07.10-P-1030CY
ENGINE 272.911 in MODEL 204.0 up to model year 2008 /AEJ 07
ENGINE 272.921 in MODEL 204.0 /2 up to model year 2008 /AEJ 07
ENGINE 272.947 in MODEL 204.0 /2 up to model year 2008 /AEJ 07
ENGINE 272.948 in MODEL 204.0 up to model year 2008 /AEJ 07
ENGINE 272.961 in MODEL 204.0 /2 up to model year 2008 /AEJ 07
ENGINE 272.971 in MODEL 204.0 up to model year 2008 /AEJ 07
Engine running is constantly monitored in order to protect the firewall catalytic converters from excessive thermal stresses if combustion misfirings occur.
If the smooth running evaluation in the ME-SFI [ME] control unit (N3/10) detects combustion misfires, the corresponding injection valve(s) (Y62) are no longer actuated after a certain number of misfires. However, no more than two injection valves are switched off at the same time.
The combustion misfires detected are due to:
- Ignition system
- Injection system
- Mechanical engine systems (e.g. valve seats, valve springs, fresh air)
- Fuel deficiency
For the smooth running evaluation the voltage signal from the crankshaft Hall sensor (B70) is evaluated via an extensive mathematical procedure accurately for the chronological uniformity between the individual combustions.
Each individual combustion must produce a characteristic acceleration at the flywheel.
In case of combustion misfirings, the flywheel mass rotates slightly slower until the next ignition (short variations in torque).
Smooth engine running signal
The following factors are taken into consideration for smooth running evaluation:
- Engine speed, engine load
- Coolant temperature
- Recognition of an uneven road surface
- Synchronization of fuel injection and firing order
- Fuel reserve signal
- Sensor adaptation (from crankshaft Hall sensor)
- Engine speed, engine load
A comparative value for the time between two combustions is calculated from these two parameters.
- Coolant temperature
More combustion misfires are permissible when the engine is cold.
- 2. 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. Thus on poor road surfaces the smooth engine running analysis is set to more sensitive.
The ME-SFI [ME] control unit receives the wheel speed signal (for detection of uniform wheel rotation) via the chassis CAN (CAN E) from the Electronic Stability Program control unit (N30/4).
- 3. Synchronization of fuel injection and firing order
The cylinder recognition is required for fault storing and evaluation.
- 4. Fuel reserve signal
If combustion misfires have been detected, a fault is stored if the fuel tank 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 LH and RH fuel level indicator sensors (B4/1, B4/2) and sends the corresponding signal via the interior CAN (CAN B) to the instrument cluster (A1).
The ME-SFI [ME] control unit receives the fuel level information from the instrument cluster via the chassis CAN.
- 5. Sensor adaptation
The smooth running evaluation is more sensitive after an adaptation of the crankshaft Hall sensor has taken place and can adapt itself to the specific smooth running qualities of the engine.
During a deceleration phase (uniform smooth running) the smooth running analysis stores the particular smooth running properties of the engine. These are required as a comparison parameter for misfire detection.
- 6. Misfire counter
The number of detected misfires is entered in the fault memory and differs by:
- Misfiring of specific cylinders
- Misfiring at "emission limit"
- Misfire "catalytic converter damaging"
The smooth engine running analysis replaces the measurement of the combustion period and combustion voltage.