Ignition System - Electronic: Operation
On ESA and I-TEC systems, the Electronic Control Unit (ECU) is pre-programmed with data for optimum ignition timing under any engine operating condition. Using data from engine sensors (RPM, engine temperature, etc.) the ECU triggers ignition system to provide a spark at precisely the right instant. See Fig 1.
On all others, as distributor shaft turns reluctor, reluctor teeth (one for each engine cylinder) pass magnetic pick-up coil assembly. As air gap changes with approach and pass of each reluctor tooth, magnetic field varies. This creates a signal in pick-up coil assembly.
Ignitor senses this signal, and turns ignition coil primary circuit on and off. This causes magnetic field in coil primary circuit to build and collapse, resulting in a voltage surge in secondary, which fires the spark plugs.