1990-1992 Ignition 1.6 Liter

1. The cam sensor sends signals to the engine computer unit (ECU) that tell it when each cylinder is ready for fuel and spark.
2. The ECU sends two drive pulses to the Igniter Module.
3. The igniter module sends out a signal to each coil to fire them. It also sends a signal to the tachometer, a signal back to the computer, and two signals for the fuel injectors.
4. The tachometer reads the RPM.

The 1993 is the same except some cars had 4 fuel injector signals.

1994-1995 Ignition I.8 Liter

1. The cam sensor sends signals to the engine computer unit (ECU) that tell it when each cylinder is ready for fuel and spark.
2. The ECU sends two drive pulses to the coil packs.to fire them.
3. The coil packs contain circuits that fire the coils and also send out a signal that goes both to the tachometer and back to the computer.
4. The tachometer reads the RPM

In 1996, the coil packs were changed and do not drive the tachometer. Instead, the computer drives it.

The CAS has two signals. One of them is assymetric and the computer looks at the longer pulse to tell when cylinder 1 is at TDC. The other signal tells the ECU when to fire the spark. These signals switch between 5 volts and zero volts.

Using the above information, the ECU synchronizes its triggers to the igniter module for a 1,6 or the coil pack for a 1.8. These triggers are only about 3 volts.

The tach signals go to the dash board. They are different depending on whether you have a 1.8 with coil packs or a 1.6 with an igniter and coils.

Spark plugs on cylinders 1 and 4 are fired in pairs and spark plugs on cylinders 2 and 3 are fired in pairs. This page may help you figure out the firing order.

For simplicity, the fuel injection signals are not shown.. The early miatas squirt the fule injectors in oairs, with cylinder 1 and 3 together and cylinders 2 and 4 together. Later miatsa have sequential injection which allows the injector to be squirted at the optimum point for each cylinder.