Table of contents: Static (without distributor)…🠇 Direct ignition (DI) 🠇
The Bosch Motronic MP3.2 uses two types of ignition coils: either static (without distributor) ignition system or direct ignition (DI).
Static (without distributor) ignition system (DIS)
Although the ignition system is called a static ignition system, its basic functions are the same as on models equipped with a conventional contactless ignition system. In static (without distributor) the Displacement Ignition System (DIS), or so-called "wasted spark system," uses two ignition coils to create a spark discharge on two spark plugs simultaneously. One cylinder creates a spark discharge on the compression stroke, and the paired cylinder does so on the exhaust stroke, where the spark does not perform any useful function, i.e. is "idle".
Therefore, two pairs of ignition coils are required for a 4-cylinder engine. Approximately 3 kV is still required to create a "wasted spark." Each ignition coil receives voltage from the ignition switch. In addition, separate connectors for each ignition coil are made between the ECU and the amplifier. In fact, the electronic control unit and amplifier consists of two separate circuits, so that each ignition coil can be turned on individually and in turn.
Direct ignition (DI)
Unlike a static ignition system, which fires two spark plugs simultaneously, some models use two boosters and four ignition coils to fire each spark plug in the firing order of the cylinders as the piston approaches TDC on the compression stroke.
The sequence is as follows: signals from the crankshaft angle sensor (CAS) are sent to the ECU when the piston of cylinder No. 1 or No. 4 is set to the TDC position, and in order to identify the piston of cylinder No. 1, the CAS sends a signal to the ECU. Upon receiving these signals, the electronic control unit activates the corresponding amplifier and thus the corresponding ignition coil produces a spark at the right moment.