Motor electronics (ME) ignition system, function - GF07.61-P-3008AMG

ENGINE 156.980 in MODEL 164, 251 up to Model Year 8 

ENGINE 156.982 in MODEL 209 

ENGINE 156.983 in MODEL 211, 219 

ENGINE 156.984 in MODEL 216, 221 up to Model Year 8 

Fig 1: Identifying Motor Electronics Ignition System CAN Communication Diagram

Courtesy of MERCEDES-BENZ USA

The ME-SFI [ME] control unit actuates the output stages of the primary circuit in the ignition coils. At ignition timing, the ME-SFI [ME] control unit interrupts the primary circuit at the ground end whereby the high voltage is induced (generated).

1. Determining the ignition angle and actuating ignition coils 

   The ME-SFI [ME] control unit evaluates basically the following input signals required to determine the ignition angle:

   • Engine load
   • Engine speed
   • Crankshaft position
   • Camshaft position
   • Coolant temperature
   • Air mass
   • Intake air pressure
   • Intake air temperature
   • Knock signal
   • Torque request via CAN
2. Ignition angle adaptation 
   1. 2.1 Catalytic converter heating up (warming-up phase) 

      In addition to increasing the idle speed, ignition angles are continuously retarded for about 20 s to bring the catalytic converters to operating temperature more quickly if:

      • Coolant temperature at start >-10°C <40°C
      • Selector lever position "P" or "N"
   2. 2.2 IDLE SPEED 

      To assist idle speed control, the ignition angles can be retarded up to a crank angle of 36° or advanced up to a crank angle of 20.

      Adjusting the ignition angle enables a faster response than adjusting the throttle valves.

   3. 2.3 Deceleration fuel shutoff 

      To prevent a sudden increase in torque, the ignition angles are retarded briefly when combustion is resumed (when fuel injection valves are actuatedY62).

   4. 2.4 Intake air or coolant temperature 

      In order to prevent a tendency to knock at an increased intake air or coolant temperature, ignition angles are adjusted at high loads depending on performance map to "retarded".

      The ignition angle is retarded if:

      • Intake air temperature > 35°C
      • Coolant temperature > 105°C
   5. 2.5 Transmission overload protection 

      In order to protect the shift elements of the automatic transmission from excessive thermal stresses during power shifts, the ignition angle is briefly retarded during the gearshift and the engine torque is thus reduced. To do this the ME-SFI [ME] control unit receives a signal via the CAN data bus from the electric controller unit (VGS).

   6. 2.6 ESP or ASR closed-loop operation 

      In order to reduce engine torque in the ESP or ASR control mode as quickly as possible, the ignition angle is retarded before adjusting the throttle valves (reducing the opening angle).

      Information on the reduction in engine torque is transmitted by the ESP control unit to the ME-SFI [ME] control unit via the CAN data bus.

   7. 2.7 Smooth engine running analysis 

      Smooth engine running is constantly monitored in order to protect the catalytic converters from excessive thermal stresses if combustion misfiring exists.

      If smooth engine running analysis detects combustion misfiring, the appropriate fuel injector or injectors is/are no longer operated after a certain number of combustion misfirings.

   8. 2.8 Knock control (AKC) 

      If uncontrolled combustion (knocking) occurs on one or several cylinders, the ignition angle is retarded on the relevant cylinder or cylinders.

   9. 2.9 AC system 

      The engine torque is increased shortly before the refrigerant compressor (A9) is switched in. In doing so, ignition angles are adjusted for a short time to "advanced" to support idle speed control.

Diagnosis 

The ignition angles can be checked using STAR DIAGNOSIS. For troubleshooting in the double ignition system, it is possible to switch off one ignition circuit each with the STAR DIAGNOSIS. A fixture for fitting the capacitive measuring device is provided in each ignition coil.

The primary current is measured via a test cable.

Fig 2: Identifying Cylinder Arrangement And Ignition Firing Order

Courtesy of MERCEDES-BENZ USA

Cylinder arrangement and ignition firing order