Smooth running control, function - GF07.10-P-1011MAW
ENGINES 156.9 in MODEL 204.0 /2 /3, 212.0 /2
Function requirements for smooth running control, general points
• Circuit 87M (engine/timing ON)
• Engine running
Smooth running control, general points
Engine running is constantly monitored in order to protect the firewall catalytic converters from excessive thermal stresses if combustion misfires occur. The ME-SFI [ME] control unit (N3/10) reads in the following sensors and signal for smooth running control:
• LH and RH hot film MAF sensor (B2/6, B2/7), engine load
• LH and RH intake camshaft Hall sensor (B6/4, B6/5), intake camshaft positions
• LH and RH exhaust camshaft Hall sensor (B6/6, B6/7), exhaust camshaft positions
• Coolant temperature sensor (B11/4)
• Accelerator pedal sensor (B37), accelerator pedal position
• Crankshaft Hall sensor (B70), engine speed
• Instrument cluster (A1), fuel level via the chassis CAN (CAN E)
• Electronic stability program control unit (N30/4) or Premium electronic stability program control unit (N30/7) (on model 212 with DISTRONIC PLUS), wheel speed signal via chassis CAN
Function sequence for smooth running control
The function sequence is described in the following Operation steps:
• Function sequence for combustion misfire detection
• Function sequence for misfire counter
• Function sequence for factors for smooth running control
Function sequence for combustion misfire detection
For the smooth running control, the signal from the crankshaft Hall sensor is evaluated using a comprehensive mathematical procedure, to check for precise uniformity of timing between individual firings. 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 (due to torque fluctuation).
If the smooth running control in the ME-SFI [ME] control unit detects combustion misfiring, the corresponding injection valve (Y62) is no longer actuated after a certain number of combustion misfires. However, no more than two injection valves are switched off at the same time.
m/s 2 - Acceleration
s - Time
That which 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 for factors for smooth running control
The following factors affect smooth running control:
• Engine speed and engine load
• Coolant temperature
• Recognition of road bumps
• 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 computes 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.
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
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 conditions. Therefore, the tolerance range for smooth running control is increased on poor road surfaces ("wash board").
The ME-SFI [ME] control unit receives the wheel speed signal (for detection of uniform wheel rotation) from the Electronic Stability Program control unit over the chassis CAN.
Synchronization of the 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 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 SAM control unit with rear fuse and relay module (N10/2) evaluates the signals from the LH and RH fuel level indicator sensors (B4/1, B4/2) and transmits the corresponding signal over the body CAN (CAN B) to the instrument cluster. The ME-SFI [ME] control unit receives the fuel level information from the instrument cluster over the chassis CAN.
Sensor adaptation
The tolerance range for smooth running control is reduced after successful adaptation of the crankshaft Hall sensor. In this way, the smooth running control 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 control is present in the MESFI [ME] control unit and can be adapted using the Xentry diagnostics if necessary.