Electronic Ignition System

Electronic controlled ignition ECU incorporates a fault monitoring circuit. If a component develops a fault that can cause knocks, circuit automatically lowers timing 11-15 degrees to avoid damage to engine. Throttle switch signals ECU to set ignition timing point at idle. At higher speeds, ECU sets firing point to obtain best possible emissions.

Knock sensor produces current within a frequency range which occurs when cylinder knocks. When ECU receives signal, it retards timing in 3 degree intervals until knocking stops. ECU progressively advances ignition timing in .37 degree steps until programmed firing point is reached, or if cylinder starts to knock again. See Fig 1 .

Coolant temperature sensor provides information to both ignition ECU and fuel injection ECU. It cuts out information signals from knock sensors when engine is cold and adjusts for engine temperature when determining firing points.

Air mass meter measures air drawn into engine by means of a wire filament located in intake air stream. A temperature of 212°F (100°C) is maintained at filament. Current needed to maintain temperature at filament is measured, providing precise information on air mass.