What is an igniter?

Question

In researching this question about the behavior of the tach on a Mazda Miata I came across references to a part called the "igniter" that apparently has a role in generating the signal that drives the tach. What is this? It has been quite a while since I've had a "modern" gasoline engined car – the last one, IIRC, was a mid-80s SAAB 900 and I don't recall an "igniter."

Answer 1

The igniter is the step up transformer that sits inline between the engine control computer and the ignition coil. It takes the low amperage signal from the computer, usually a 12 volt square wave, and steps it up to higher amperage trigger signal for the ignition coil. Most use a high current rated transistor as its primary component. This circuit design protects the PCM by removing a high current device that is a common failure part from being part of an expensive engine control computer. It sometimes has a terminal that is used to supply the tach signal.

In engines with distributor and electronic engine control it is usually a separate part, often located in the distributor.

In early electronic ignition systems that do not use an engine control computer the igniter often was located in the distributor and included a pick-up coil as part of the igniter unit. Thus becoming electronic distributor points.

In engines with coil on plug (COP) type ignition system design a transistor for this purpose is usually incorporated into each coil. Most systems of the last decade use COP units as a way to control ignition timing to each cylinder individually to compensate for differences in cylinder conditions. This is done to improve emissions, power and fuel consumption.