Smooth running control, function - GF07.10-P-1011MI

ENGINE 272.9 (except 272.982) in MODEL 204.0/2 as of model year 2009 

ENGINE 272.9 (except 272.983) in MODEL 212 

ENGINE 272.9 (except 272.984) in MODEL 207 

ENGINE 272.9 in MODEL 204.9 

ENGINE 273.9 in MODEL 207, 212 

Function requirements for smooth running control, general points 

• Circuit 87M ON (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 overloading if combustion misfirings occur. The ME-SFI [ME] control unit (N3/10) reads in the following sensors and signal for smooth running control:

• hot film MAF sensor (B2/5), engine load
• left and right intake camshaft Hall sensor (B6/4, B6/5), intake camshaft positions
• left and right 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 Electronic Stability Program Premium control unit (N30/7) (for DISTRONIC PLUS), wheel speed signal via the chassis CAN

Function sequence for smooth running control 

The function sequence is described in the following 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 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 (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.

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

What is detected is combustion misfiring caused by:

• ignition system
• injection system
• mechanical engine components (e.g. valve seats, valve springs, unmetered air)
• fuel starvation

Smooth running signal 

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.

Recognition of road bumps 

Vibrations transmitted through the drivetrain 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 via the chassis CAN.

Synchronization of fuel injection and firing order 

Cylinder identification is required for fault storage and assessment, 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 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 over 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 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 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 control	MODEL 204	PE07.10-P-2711-97FAB
		MODEL 207	PE07.10-P-2711-97EAB
		MODEL 212	PE07.10-P-2711-97DAB
	Overview of system components motor electronics (ME-SFI) fuel injection and ignition system		GF07.61-P-9997MI