In the parametric ignition system, the optimal ignition timing is determined depending on the current engine operating mode. Control parameters are engine speed, engine temperature, intake air temperature (only on four-cylinder engines) and engine load. The engine load degree refers to the current engine load, for example, there is a difference in engine operation at 4000 rpm when the vehicle is uphill or downhill. On four-cylinder engines, the degree of engine load is determined by the transmitted intake manifold pressure and throttle valve position, and on six-cylinder engines by the intake air quantity.
The required field of control parameters of the ignition system was determined as a result of research on the stands and refined in sea trials so that as a result, optimal values were obtained in terms of fuel consumption, exhaust gas composition and driving performance. The values obtained are stored in the memory of the electronic control unit
While driving, the control unit receives information about the current engine speed, its temperature and load, on the basis of which the optimal ignition timing is generated for the current conditions (e.g. 10°BTDC or 0°).
In addition to these control parameters, on engines with an ignition system that does not have moving parts, the ignition timing is also determined from the knock sensor. Since fuel consumption is minimal at a high compression ratio, modern engines have the highest possible compression ratio. However, at a high compression ratio, uncontrolled combustion of the fuel, i.e. detonation, can occur. Over time, detonation can damage the engine. To avoid this, a knock sensor is installed that registers uncontrolled combustion and transmits information to the control unit, which at the same time ensures the installation of a later ignition. On BMW vehicles, 2 knock sensors are installed on the engine block, connected by electrical wires to the DME control unit.
In the absence of information about the number of revolutions, the degree of load, etc. deterioration in driving performance, such as a reduction in engine power, may occur. It is also possible to increase fuel consumption. Long-term engine failures are not to be feared if the defect is corrected at the earliest opportunity. In the event of a misfire, the DME is switched off, thereby protecting the catalyst from overheating.
The ignition distributor with a parametric ignition system on models 316i, 318i produced before August 1993 has another task, namely the distribution of ignition voltages to individual spark plugs. The distributor runner is driven directly from the camshaft. At the same time, inertial weights, a vacuum membrane and a system of inductive sensors are not required, since their functions are performed by a microprocessor in the control unit
The ignition system on all engines is virtually maintenance free and operates flawlessly with no ignition timing adjustment required.