Smooth engine running analysis, function - GF07.10-P-1030MIS

ENGINE 272.9 in MODEL 221.0 /1 as of model year 2009 / AEJ 08 

ENGINE 273.9 in MODEL 216.3, 221.0 /1 as of model year 2009 / AEJ 08 

Function requirements for smooth engine running analysis, general points 

• Circuit 87M ON (engine control ON)
• Engine running

Smooth engine running analysis, general points 

Engine running is constantly monitored in order to protect the firewall catalytic converters from excessive thermal stresses if combustion misfires occur.

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

• Hot film MAF sensor (B2/5), engine load
• LH and RH intake camshaft Hall sensors (B6/4, B6/5), intake camshaft positions
• LH and RH exhaust camshaft Hall sensors (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) and central CAN (CAN F)
• ESP control unit (N47-5) or regenerative braking system control unit (N30/6) (for Hybrid), wheel speed signal via the chassis CAN

Function sequence for smooth engine running analysis 

The function sequence is described in the following steps:

• Function sequence for combustion misfire detection 
• Function sequence for misfire counter 
• Function sequence factors for smooth running evaluation 

Function sequence for combustion misfire detection 

For analyzing smooth engine running, the signal supplied by the crankshaft Hall sensor is analyzed using a sophisticated mathematical method to determine whether exact time synchronism exists between the 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 evaluation in the ME-SFI [ME] control unit detects combustion misfiring, the corresponding fuel injection valve (Y62) is no longer actuated after a certain number of combustion misfires. However, a maximum of two fuel injection valves may be 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 engine running signal 

What 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 factors for smooth running evaluation 

The following factors affect smooth running evaluation:

• Engine speed and engine load 
• Coolant temperature 
• Recognition of an uneven road surface 
• Synchronization of the 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 calculates 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 an uneven road surface 

Vibrations transmitted through the drive train may have a negative effect on engine running at certain engine speeds and load states. Therefore, the tolerance range for smooth running evaluation 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) via the chassis CAN from the ESP control unit or the regenerative braking system control unit (for Hybrid).

Synchronization of the fuel injection and firing order 

Cylinder detection on the signals from the crankshaft Hall sensor, and from the intake camshaft Hall sensors or the exhaust camshaft Hall sensors, is required for fault storage and assessment.

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 fuel level sensors in the LH and RH fuel tank halves (B4/1, B4/2) and sends the corresponding signal via the interior CAN (CAN B) to the instrument cluster.

The ME-SFI [ME] control unit receives the fuel level information via the chassis CAN and central CAN from the instrument cluster.

Sensor adaptation 

The tolerance range for smooth running evaluation is reduced after successful adaptation of the crankshaft Hall sensor.

In this way, the smooth running evaluation 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 evaluation 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 evaluation	Model 216	PE07.61-P-2770-97CAB
		Model 221	PE07.61-P-2770-97SAB
	Component description for ME-SFI [ME] control unit	N3/10 Engine 272 except 272.974 (Hybrid)	GF07.61-P-6000MIS
		N3/10 Engine 272.974 (Hybrid)	GF07.61-P-6000MEH
		N3/10 Engine 273	GF07.61-P-6000MLS