Ignition System Components: Coils, Modules and Spark Plug Wires

Ignition System Components: Coils, Modules and Spark Plug Wires

Learn how spark plugs, ignition coils, and ECM controls work together to ignite the air-fuel mixture and keep your engine running smoothly.


We all know that vehicles run on gasoline. I think that we can also agree that gasoline is a very flammable fluid. Did you ever wonder how this fuel actually runs an engine and how it gets ignited to do so? Yes, it’s very flammable, but it needs two other components to ignite. It must have oxygen and an ignition source. In our vehicles today, this source is the ignition system. Today, we are going to look into the system and its components. At the very root of the system is the actual part that supplies the spark to ignite. We all know that as the spark plug. But how does the spark plug convert electrical energy into a spark and how is it controlled? Early systems used a combination of points, condenser, and a distributor to get the spark to the fuel. In this system, the charge from the battery would build up in the coil until the points broke and grounded the coil, thus discharging the spark to the distributor and through the wires to the plug.

The spark plug is an igniter of sorts. It is grounded to the block via the threads in the metal portion of the plug. A separate conductor insulated in porcelain carries the voltage to the center electrode. At this point, the voltage builds up and arcs across to the grounded electrode and boom, we have ignition. The air fuel mixture that has gathered in the combustion chamber ignites and the controlled burn across the top of the piston pushes it down the cylinder. In today’s internal combustion engines, the process is still basically the same.

However, some of the components have morphed into different forms and some have been replaced by newer, more efficient versions. Today, there is one coil for every cylinder. Each coil sits directly on top of the spark plug via a rubber boot through the valve cover. The spark plug wires, the points and the distributor have been replaced by computer controls in the electronic control module or ECM. Voltages at the plugs are much greater and thus gaps have been widened to give more robust sparks. At the heart of all of it, still is the spark plug. Compositions have changed over the years. We have gone from steel to copper, to platinum, and now onto Iridium. Plug life has increased from 5,000 miles to 100 000 miles. Today’s ignition systems are more precise and last much longer. They still need maintenance and service regularly. That’s about all for today and thanks for being with us.

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