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

Engine 264.9 in Model 205, 253 

Ignition system, general points 

Each cylinder is equipped with a directly inserted ignition coil. The ME-SFI [ME] control unit (N3/10) reads in the following signals for the ignition system:

• Knock signal

  Knock sensor 1 (A16/1)

  Knock sensor 2 (A16/2)

• Intake camshaft position

  Intake camshaft Hall sensor (B6/15)

• Exhaust camshaft position

  Exhaust camshaft Hall sensor (B6/16)

• Coolant temperature

  Coolant temperature sensor (B11/4)

• Engine load

  Pressure and temperature sensor downstream of throttle valve (B28/27)

• Engine speed and crankshaft position

  Crankshaft Hall sensor (B70)

The requirements of the torque coordination function are also taken into account.

For the following partial functions, ignition angle adjustment in the direction "retarded" or "advanced" takes place:

• Idle speed control
• Inertia fuel shutoff
• Transmission overload protection
• Knock sensor system
• Torque coordination

The ME-SFI [ME] control unit transmits the signal for the dwell time of the respective operating point to the following component parts via the actuation line (circuit 4):

• Cylinder 1 ignition coil (T1/1)
• Cylinder 2 ignition coil (T1/2)
• Cylinder 3 ignition coil (T1/3)
• Cylinder 4 ignition coil (T1/4)

The respective ignition coil interrupts the primary circuit after expiry of the dwell time. The ignition voltage passes from the ignition coil to the spark plug and causes arcing in the air gap between the center and ground electrodes.

The ignition angle is determined in a characteristics map-dependent manner according to the input signals from the ME-SFI [ME] control unit.

Operating mode of ignition coil 

Single spark ignition 

The ignition coil is usually charged for an Engine running at its normal operating temperature once per ignition cycle and an ignition spark is generated. 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.

The option also exists to use multiple sparks per ignition process instead of just one. This operating mode is called multi-spark ignition.

Multi-spark ignition 

In contrast to single spark ignition more sparks are used 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 sparks. 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 interrupted at the ignition timing whereby the ignition spark is created. The ignition coil is not completely discharged in Multispark ignition mode.

The flowing secondary current which directly depends on the charge level of the ignition coil is measured in the ignition coil. If it drops below the secondary current threshold, the coil electronics switches the power amplifier to conducting again, whereby the charging current flows again.

The level of the flowing primary current is also monitored. If the primary current threshold is reached, the power amplifier closes the primary circuit and it comes again to generation of a high voltage. This produces a further spark. The following sparks are generated according to the same scheme.

Diagnosis:

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

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

Courtesy of MERCEDES-BENZ USA

Firing order 

Courtesy of MERCEDES-BENZ USA

	Electrical function schematic for ignition system		PE07.10-P-2705-97FBI
	Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-P-9998MRS