4

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."

1 Answer 1

3

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.

2
  • So, it's there to drive the current needed by the coil since the ECUs typically aren't designed to handle high current loads? Is it something that is usually or always there these days? Is it actually a transformer or is it a high-current transistor?
    – dlu
    Commented Nov 20, 2016 at 23:23
  • @dlu see my additions to my answer. Commented Nov 21, 2016 at 0:52

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .