Theory of Operation

The job of the ignition system is to generate a spark that will ignite the fuel-air mixture in the cylinder of an engine. It must do this at exactly the right instant and do it at the rate of up to several times per minute for each cylinder in an engine. If the timing of that spark is off by a small fraction of a second, the engine will run poorly or not run at all. This ignition system sends an extremely high voltage to the spark plug in each cylinder when the piston is at TDC or top dead center of its compression stroke. The tip of each spark plug contains a gap that the voltage must jump across in order to reach ground. That is where the spark happens.

The voltage that is available to the spark plug is somewhere between 20,000 volts and 50,000 volts or higher. The job of the ignition system is to produce that high voltage from a 12 volt source and get it to each cylinder in a specific order, at exactly the right time.

The ignition system has two tasks to perform. First, it must create a voltage high enough (8,000+) to arc across the gap of a spark plug, thus creating a spark strong enough to ignite the air/fuel mixture for combustion.

Second, it must control the timing of that the spark so it occurs at the exact right time and send it to the correct cylinder.

The ignition system is divided into two sections, the primary circuit and the secondary circuit. The low voltage primary circuit operates at battery voltage (12 to 14.5 volts) and is responsible for generating the magnetic field to fire the spark plug at the right time and send that signal to the ignition coil. The ignition coil secondary is the component that converts the 12 volt signal into the high 8,000+ volt charge. Once the voltage is stepped up, it goes to the ignition wire circuit which then directs the charge to the correct spark plug at the right time.