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

ENGINE 113.990 in MODEL 211, 219 

ENGINE 113.991 in MODEL 215, 220 

ENGINE 113.992 in MODEL 230 

ENGINE 113.993 in MODEL 463 

ENGINE 113.995 in MODEL 230 

Fig 1: Motor Electronics Ignition System Function Diagram

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:

   • Crankshaft position,
   • Camshaft position,
   • Coolant temperature,
   • Charge air temperature,
   • Charge air pressure,
   • Knock signal,
   • Torque request via CAN

   and interrupts at the ground end the ignition coil ignition coil primary circuit in the very ignition timing moment.

2. Ignition angle adaptation 

1. 2.1 Catalytic converter heating up (warming-up phase) 

   In addition to increasing the idle speed, the 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
2. 2.2 Idle 

   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 valve.

3. 2.3 Inertia fuel shutoff 

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

4. 2.4 Charge air/coolant temperature 

   To prevent the tendency to knock at increased charge air temperatures and coolant temperatures, depending on performance maps, the ignition angles are retarded at high load.

   The ignition angle is retarded if:

   • Charge air temperature > 35°C
   • Coolant temperature > 100°C
5. 2.5 Transmission overload protection 

   To protect shift elements of the automatic transmission from thermal overloads during power shifts (1-2, 2-1), the ignition angles are retarded briefly during the shift operation thereby reducing the engine torque. The ME control unit is supplied with a signal over the CAN databus by the ETC control unit for this purpose.

6. 2.6 ESP/ASR control mode 

   To reduce engine torque in the ESP/ASR control mode as quickly as possible, the ignition angle is retarded before adjusting the throttle valve (reducing the opening angle). The 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 the 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 Anti-knock control (AKC) 

   If uncontrolled combustion (knocking) occurs at one or several cylinders, the ignition angle at the relevant cylinder or cylinders is "Retarded".

9. 2.9 Double ignition 

   Two spark plugs for each cylinder are beneficial because of the arrangement of the valves for achieving optimal emission levels and smooth engine running. Each spark plug is actuated separately via its own ignition coil by the ME control unit. Both ignition coils of a cylinder are combined to form a dual ignition coil.

   Both ignition sparks of one cylinder are released simultaneously and always with optimal power.

   The high voltage distribution is performed smoothly (i.e. without mechanical ignition distributor).

For troubleshooting in the double ignition system, it is possible to switch off one ignition circuit each with STAR DIAGNOSIS.

The ignition angles can be checked using STAR DIAGNOSIS.