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Ignition System Function - GF07.10-P-1005MNA

Engine 177.9 in model 205, 253 

Engine 177.9 in model 213 

up to model year 2021 

Function requirements, general 

IMPORTANT The electronic ignition lock control unit (N73) transmits the status of circuit 15 via the chassis FlexRay (Flex E), the powertrain control unit (N127) and the drive train CAN (CAN C1) to the ME-SFI [ME] control unit (N3/10). The ME-SFI [ME] control unit then actuates the circuit 87M relay (K40/8kN). The circuit 87M relay switches the battery voltage (circuit 30) to circuit 87M. When circuit 87M is switched through to the ME-SFI [ME] control unit, it starts the engine management.

Ignition system 

Each cylinder is equipped with its own ignition coil. 2 ignition coils are each combined in one housing:

The ME-SFI [ME] control unit reads in the signals of the following sensors for controlling the ignition system:

The ME-SFI [ME] control unit also takes the torque coordination requirements into consideration.

The ME-SFI [ME] control unit issues the signal for ignition via the control line. The ignition coil interrupts the primary circuit. A high-voltage pulse is generated in the secondary coil, which leads to arcing in the air gap between the center electrode and the ground electrode at the spark plug.

Single spark ignition 

The ignition coil is usually charged for an engine running at its normal operating temperature once per ignition cycle, in order to generate an ignition spark. Ignition coils with high energies can be used to securely ignite the mixture, also in cold start conditions, which allow a long spark ignition period. There is also the option of generating several sparks per ignition procedure rather than just one spark. This operating mode is called multi-spark ignition.

Multi-spark ignition 

In contrast to single spark ignition more sparks are generated for multi-spark ignition. This is not a series of a number of single sparks occurring one after the other but instead the ignition coil is recharged in-between in order to again provide sufficient energy for a spark. A multi-spark ignition begins like a single spark ignition. The ignition coil is supercharged at the beginning up to a desired target primary current. The charging current is switched off at the ignition timing whereby the ignition spark is created. However, the ignition coil is not fully discharged. The secondary current is measured in the ignition coil. If it drops below a defined threshold, the coil electronics switches the power amplifier to conducting again, whereby the charging current flows again. The level of the primary current is also monitored. If the primary current threshold is reached, the power amplifier closes the primary circuit and it comes again into high voltage generation mode. This produces a further spark. The following sparks are generated according to the same scheme.

IMPORTANT The ignition angles can only be checked using the diagnostic tester.

Ideal development of the primary and secondary current for a multi-spark ignition 

G13770146Courtesy of MERCEDES-BENZ USA

IMPORTANT The firing order of the engine is: 1, 5, 4, 2, 6, 3, 7, 8.

  Electrical function schematic for ignition system Engine 177.9 in model 205, 253 PE07.10-P-2705-97FBD
    Engine 177.9 in model 213 up to model year 2021 PE07.10-P-2705-97DBG
  Overview of system components for gasoline injection and ignition system with direct injection Engine 177.9 in model 205, 253 GF07.70-P-9998MNA
    Engine 177.9 in model 213 up to model year 2021 GF07.70-P-9998MNE
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