Smooth Running Control, Function - GF07.10-S-1011TRC

Engine 274 in model 447, 448 

except code XM0 (Facelift) 

Function requirements for smooth running control, general points 

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

Smooth running control, general points 

Engine running is constantly monitored in order to protect the catalytic converter from thermal overload if combustion misfiring occurs.

The ME-SFI [ME] control unit (N3/34) needs the following sensors and signal for smooth running control:

• Intake camshaft Hall sensor (B6/29) over direct line
• Intake camshaft Hall sensor (B6/30) over direct line
• Coolant temperature sensor (B11/21) over direct line
• Intake manifold pressure sensor (B28/24) over direct line
• Crankshaft Hall sensor (B70/2) over direct line
• Electronic Stability Program control unit (N30/4), wheel speed via the chassis CAN (CAN E)

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 position 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 multiple wheel which is located on the crankshaft. If there are combustion misfires, the multiple 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 fuel injector (Y62) 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
• Mechanical engine components (for example, valve seats, valve springs, unmetered air)
• Fuel injection system
• 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 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.

Synchronization of injection and firing order 

Cylinder detection is required for fault storage and evaluation using the signals from the crankshaft Hall sensor and the intake camshaft Hall sensors or the 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 combustion misfire detection.

	Electrical function schematic for smooth running control	Engine 274 in model 448 except code XM0 (Facelift)	PE07.10-S-2711-97VDC
		Engine 274 in model 447 except code XM0 (Facelift)	PE07.10-S-2711-97TRC
	Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-S-9998TRC