What Are the Pencil Ignition Coils?

An ignition coil is the heart of any car’s electrical ignition system, and it converts a low voltage current from the vehicle battery into high voltage energy to ignite the air/fuel mixture in a spark plug. A poor or failing coil can cause a car to run poorly, and in some cases even fail to start. When this happens, it is common to blame the ignition coils for a no-start situation, but in reality the coils are only one piece of a much larger ignition system.

In addition to the ignition coil itself, there are several other components that work together to generate the high voltage needed to fire a spark at each of the engine’s spark plugs. These include a crank angle sensor that monitors the position of the camshaft within the engine to determine when to fire the spark plugs, and a distributor that distributes the generated high voltage throughout the engine.

The classic can-type ignition coils used in cars and motorcycles use a magnetic core to generate high voltage by passing alternating current through copper wire windings placed around the core. These primary and secondary windings feature insulating materials to prevent short circuits. When the coil is activated by battery current, the magnetic field in the core collapses, generating a high voltage that can be fed directly to the spark plug through the ignition leads.

Pencil Ignition Coils

A pencil coil is a successor to the classic can-type ignition coil, but is smaller and lighter so it can be mounted above each spark plug in an engine’s cylinder head. This design reduces power loss from energy transfer between the ignition coil and spark plug, as well as taking up less space in the engine compartment. This type of coil is typically found in 2 to 16 cylinder inline and V-type engines.

Tech Tip: Checking your ignition coils can be a simple task using a multimeter. Connect the positive and negative leads to the corresponding terminals on your coil, as specified by the repair manual or online information. If your coils are working correctly, the resistance between the primary and secondary winding should be the same. If they are not, then the ignition coil is damaged or shorted out internally.

Coil-on-Plug

A “Coil-on-Plug” or “coil-on-plug” ignition system replaces the mechanical distributor with a computer controlled unit called an engine control module (ECU). An ECU is able to monitor various sensors within the engine, including the camshaft position sensor, as well as the crankshaft position sensor and other engine parameters. The information from these sensors is fed into the engine computer, which then adjusts the timing and other variables to match what it knows about the relationship between the pistons and valves within the engine to create the best combustion conditions. A newer ECU is capable of analyzing all of this data and determining what changes need to be made in the ignition timing, and it can then send these data to the individual ignition coils to perform the proper functions for that cylinder.