Synchronize fuel injection and firing order function - GF07.10-P-1006MM

ENGINE 276.9 in MODEL 204 

ENGINE 276.9 in MODEL 207, 212 (except 212.095), 218 up to model year 2014 

Function requirements synchronization of fuel injection and firing order, general points 

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

Synchronization of fuel injection and firing order, general points 

Synchronization of the injection and firing order is processed by the ME-SFI [ME] control unit (N3/10) in order to actuate the ignition coils (T1) and fuel injectors (Y76).

Furthermore, synchronization is required for knock control and fuel shutoff on the individual cylinders.

The ME-SFI [ME] control unit synchronizes the injection and firing order using the signals from the following sensors:

• Crankshaft Hall sensor (B70), engine speed and crankshaft position
• 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

Function sequence for synchronization of the fuel injection and firing order 

The function sequence is described in the following steps:

• Function sequence for synchronization 
• Function sequence for coasting detection 
• Function sequence for engine speed signal 

Function sequence for synchronization 

When the engine is started, the injection sequence is determined according to the firing order, using the voltage signals from the crankshaft Hall sensor and the intake camshaft or exhaust camshaft Hall sensors. To do this the ignition TDC (T  op D  ead C  enter) of cylinder 1 must be recognized.

At the 2nd negative signal edge following the gap in the signal from the crankshaft Hall sensor, the ME-SFI [ME] control unit detects the TDC position in cylinders 1 and 6. If the signal from an intake camshaft Hall sensor is at 0 V (low) at this time, the ME-SFI [ME] control unit processes it to detect ignition TDC in cylinder 1.

If the voltage signal from a camshaft Hall sensor is missing, the voltage signal from another camshaft Hall sensor is taken in a certain sequence and used as a replacement to detect ignition TDC in cylinder 1.

If no voltage signal is available from any of the camshaft Hall sensors, ignition and injection take place after 360° CKA (C  rankshaft A  ngle) in order to allow an emergency start.

Function sequence for coasting detection 

When the engine is shut down, coasting detection takes place, which also evaluates the engine turn back shortly before standstill.

During a computer run on from the ME-SFI [ME] control unit, the determined rest position of the crankshaft as a °crank angle is stored and used for the next engine start.

If coasting detection does not produce a result, or the engine has been turned while shut down, injection and firing order are synchronized at engine start.

Function sequence for engine speed signal 

Using the signal from the crankshaft Hall sensor (), the ME-SFI [ME] control unit () generates the short-circuit-proof engine speed signal (for example for cold testing and diagnosis) and sends it via the chassis CAN (CAN E).

When the crankshaft is turning, a voltage signal (AC voltage) is generated in the crankshaft Hall sensor by the teeth on the increment wheel (perforated plate). Here, each tooth generates a voltage pulse. No voltage is generated at the gap where there are 2 missing teeth. The engine speed signal is a square wave signal with a constant on/off ratio of 6 pulses per engine revolution (60° CA) and a maximum current of approx. 20 mA.

If the voltage signal from the crankshaft Hall sensor drops, the voltage signals from the LH and RH intake camshaft Hall sensors or the LH and RH exhaust camshaft Hall sensors are used instead (in limp-home mode).

Fig 1: Synchronize Fuel Injection And Firing Order Function Graph

Courtesy of MERCEDES-BENZ USA

Signal assignment