Smooth Running Control, Function - GF07.10-P-1011MNC

Engine 276.8 in model 172.4 

Function requirements for smooth running control, general points 

• Circuit 87M (Engine management ON)
• Engine runs

Smooth running control, general points 

Engine running is constantly monitored in order to protect the catalytic converters from excessive thermal overloading if combustion misfirings occur.

For smooth running control, the ME-SFI [ME] control unit (N3/10) reads in the following signals:

• Left and right intake camshaft hall sensors (B6/4, B6/5), intake camshaft positions
• Left and right exhaust camshaft hall sensors (B6/6, B6/7), exhaust camshaft positions
• Coolant temperature sensor (B11/4), coolant temperature
• Pressure sensor downstream of throttle valve (B28/7), engine load
• Crankshaft Hall sensor (B70), engine RPM
• Electronic Stability Program control unit (N30/4), wheel speed signal over chassis CAN 1 (CAN E1)

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 sensor rotor (perforated plate).

If there are combustion misfires, the sensor rotor turns up to the next ignition somewhat slower (torque fluctuation).

If the smooth running control in the ME-SFI [ME] control unit detects combustion misfiring, the corresponding fuel injector is no longer actuated after a certain number of combustion misfires. However at least two fuel injectors are 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 running signal 

Courtesy of MERCEDES-BENZ USA

What is detected is combustion misfiring caused by:

• Ignition system
• Fuel injection system
• Mechanical engine components (for example, valve seats, valve springs, unmetered air)
• Fuel starvation

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 injection and firing order 
• 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 evaluation of the engine running at certain engine speeds and load conditions. Therefore, the tolerance range for smooth running control is increased on poor road surfaces.

The ME-SFI [ME] control unit receives the wheel speed signal (for recognition of even wheel turning) via the chassis CAN 1 from the ESP control unit.

Synchronization of 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.

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 saves 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 ME-SFI [ME] control unit and can be adapted using the Xentry diagnostics if necessary.

	Electrical function schematic for smooth running control		PE07.10-P-2711-97TAH
	Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-P-9998MNC