Models 260 and 300 with EZL ignition system
The EZL ignition system includes spark plugs, high-voltage wires, ignition distributor, ignition coil and electronic control unit ECU together with sensors, actuators and electrical wires. The operating principle of the ignition system is the same regardless of the location of the units and elements of the ignition system depending on the car model.
The ignition control unit supplies voltage to the primary winding of the ignition coil. At the required moment, the control unit disconnects the voltage from the ignition coil, which leads to a drop in the magnetic field in the primary winding and induces high voltage in the secondary winding of the ignition coil. High voltage at a certain moment from the ignition coil through the ignition distributor and high-voltage wires is supplied to a certain spark plug. When high voltage is supplied to the spark plug, a spark is formed between the electrodes of the spark plug, which ignites the fuel-air mixture in the engine cylinder. The moment of ignition of the fuel-air mixture is determined by an electronic control device.
The ignition timing is determined and continuously adjusted by the electronic control unit (ECU) based on information about engine speed, crankshaft position and vacuum in the intake manifold, received from sensors installed on the engine. Information about the throttle position is also taken into account when determining the ignition timing (removed from the throttle position switch), the temperature of the air entering the engine and the temperature of the coolant.
Based on the information from the camshaft sensor, the ECU determines in which of the cylinders the fuel is currently igniting. The sensor, installed in the cylinder head, induces a signal when the protrusion on the end of the camshaft sprocket, which controls the intake valves, passes near it. As a result, the ECU controls the ignition timing individually for each cylinder, which in turn allows for control of detonation in the cylinders.
On ignition systems with knock control, the knock sensor is mounted on the cylinder block. The knock sensor detects premature ignition before the detonation manifests itself as a knock of the piston pins. When detonation occurs, the ECU reduces the ignition timing in that cylinder. Then, by gradually increasing the ignition timing in that cylinder, the ECU restores its original value until new detonation occurs.
Depending on the type of fuel used, the initial ignition timing can be changed using a changeover plug located in the engine compartment next to the ECU.
Models 280 and 320 - 24V with HFM engine management system
The HFM engine management system is a stand-alone system that simultaneously controls the ignition and fuel injection systems.
The operation of the HFM system is similar to the operation of the EZL ignition system with the following differences.
The HFM ignition system does not have a distributor. The ignition unit consists of three ignition coils. Each ignition coil consists of two separate high-voltage windings that deliver a spark to two cylinders simultaneously. The ignition pulse is delivered to two spark plugs for each engine cylinder at once, one on the compression stroke and one on the exhaust stroke. The ignition spark on the exhaust stroke does not affect the operation of the engine and is therefore wasted. The ECU uses inputs from various sensors to calculate the required ignition timing and the energy accumulation time on the ignition coil.
(Information copied from the website www.mercedesman.ru)
To detect faults in the engine management system, it is necessary to use special electronic measuring devices, and this work must be carried out at a service station.