Automotive Ignition Systems: An Easy-to-Follow Guide

The key you turn or the button you push to start the vehicle is often called the ignition. But, why? There is nothing being lit on fire here, right? All you are doing is providing energy to the ignition system of the vehicle. Once this happens, a spark is generated so that the air and fuel mixture in the internal combustion chamber can be ignited. The only exception is with diesel engines because they don’t use spark plugs to ignite the mixture. Instead, the air that is added to the fuel will cause an ignition on its own. When these things don’t happen correctly is when you’ll find yourself unable to start your vehicle.  If you’re not at home you will require a tow truck.

The car battery contains approximately 12 volts of electricity. The ignition coil takes these 12 volts and converts them into a much higher voltage, which then gets transmitted to the spark plugs through the ignition wires. Newer vehicles have the ignition coils attached above the spark plugs. The engine control unit, which is the central computer of the vehicle, will fire them up rather than the mechanical distributor. The spark plugs are attached to the cylinder head with screws. When the sparks are generated, they go right into the internal combustion chamber where the air and fuel mixture reside, then ignites it at the appropriate timing. If this doen’t happen then you may require assistance from a tow truck service.


car engine under the hood

The Timing of the Ignition

It is crucial that the spark plug ignites the air and fuel mixture within the cylinder at the appropriate time. This will determine the quality of the engine’s performance. Ignition timing is the term which refers to the spark’s timing in the cylinder. The engine control unit is what controls the timing automatically through a series of sensors which helps it know when the right times will be. This is much more accurate than the older technology that relied on mechanical and vacuum mechanisms to determine the ignition timing.

An engine has multiple cylinders with air and fuel mixtures in them. The ignition timing for each cylinder is controlled separately by the engine control unit. This ensures that you get the most efficiency possible out of your engine. Any new car today will have a crank position sensor, also known as a cam position sensor, which is connected to the engine control unit. This helps the control unit know the location of the cylinder’s pistons as they do their 4 up-and-down strokes.

straight six cylinder engine

Ignition Systems That Are Distributor-Based

Before we had engine control units to electronically manage the ignition systems of vehicles, there were only distributors to do this job. The power would get transferred to the ignition coil and then the ignition timing would be modified. The coil would have a high amount of voltage that would get transferred to the spark plugs. However, newer cars don’t really use distributors hardly at all. When they are used, it is just to transfer voltage to the wires of the spark plug.

The distributor’s interior has a rotor which functions from a camshaft at 50% the engine’s RPM. This allows the rotor to rotate in there. The distributor cap will likely have a central terminal that transfers energy to the rotor from the ignition coil. This causes the rotor to rotate past various contacts, like the spark plugs.

The rotor never touches the contacts as it passes them within the distributor cap. There is just a small gap of space between them. So, each time the rotor goes by a contact, the ignition coil’s electrical pulse hops over this small space and goes into the spark plug through its ignition wire.


Direct Ignition Systems

There is no distributor in a direct ignition system. The ignition coils are directly connected to the spark plugs by the ignition wires. The engine control unit controls the timing of the ignition. You may find one separate ignition coil used for each spark plug in the direct ignition system. Other versions of the system only have one coil used for multiple spark plugs.

A lot of new engines today will have an individual ignition coil per engine cylinder, which is located on top of the spark plugs.  Because of this, length ignition wires carrying high amounts of voltage are not required.

insulated spark plug

Spark Plugs

Gasoline engines are all equipped with spark plugs. The purpose of a spark plug is to create the spark needed to ignite the mixture of fuel and air within each cylinder of the engine. The mixture will expand once this happens, causing the piston in the cylinder to get pushed down.

Each spark plug has a side electrode and center electrode. After the spark plug receives the voltage from the ignition system, a spark hops between these two electrodes. This space which exists between these electrodes is called the “gap.” A higher amount of voltage will be needed if the gap is too big. That is okay, though, because a wider gap will make it easier for the spark to ignite the air and fuel mixture and create an overall better performance from the engine. However, wide gaps can also become easily contaminated with oil or fuel too. So, you need to keep the gap at just the right length.

You may find some types of spark plugs with multiple ground electrodes which are supposed to give them better contact with the air and fuel mixture.