Initial Inspection and Diagnostic Overview

GF07.10-P-1030V Smooth Engine Running Analysis, Function







To protect the catalytic converters from thermal overload through combustion misfirings and in order to keep the exhaust emission values, the engine operation is continuously monitored. If smooth engine running analysis in the ME-SFI [ME] control unit detects combustion misfiring, the fuel injection valves affected are no longer actuated after a certain number of misfiring.

The following combustion misfiring causes are detected:
- Ignition system
- Injection system
- Engine, mechanical aspects (e. g. fresh air, valve seat, valve springs)
- Fuel shortage







For smooth engine running analysis the signal supplied by the Hall sensor is analyzed exactly in respect of time uniformity between the individual combustions by means of a comprehensive mathematical method.

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).

The following factors are taken into account:
- Engine speed, engine load
- Engine temperature
- Recognition of uneven road surface
- Synchronization of fuel injection and firing order
- Fuel reserve signal
- Sensor wheel adaptation takes place.

1. Engine speed, engine load
A comparative value for the time between two combustions is calculated from these two parameters.

2. Engine temperature
If engine is cold, several combustion misfires are allowed temporarily.

3. Recognition of uneven road surface
The wheel speed signal is sent via the CAN data bus from the traction systems control unit (even run). On poor road surfaces (washboard roads) the smooth engine running analysis is set less sensitive. Vibrations transmitted through the drive train may have a negative influence on the smooth operation analysis at certain engine speeds and load states.

4. Synchronization of fuel injection and firing order
The cylinder recognition is required for fault storing and evaluation.

5. Fuel reserve signal
If combustion misfires are 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.

6. Sensor wheel adaptation
After sensor adaptation is performed, the smooth engine running analysis becomes more sensitive and can be adapted to the specific smooth running properties 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.

Misfire counter
The following information is entered in the fault memory:
- Total of all misfirings
- Misfiring of specific cylinders
- Misfiring at "emission limit"
- Misfiring "harmful to catalytic converter"