Your (previous) column claimed that “many newer cars don’t have spark plug wires.” So how does the electricity get to the spark plugs to make a spark?

Gary Wedemeyer, Seattle

Good question, Gary. A majority of recent vehicles have distributorless ignition systems, which eliminates a handful of sometimes problematic conventional components. Let’s take a look at how a distributor works, to gain greater appreciation for its retirement.

An ignition system’s job is to create a high-voltage spark at precisely the right instant and successfully deliver it to the spark plugs, igniting the air-fuel mixture. A distributor, driven by the engine’s camshaft, typically contains a position-sensing device and ignition-control module within its midsection, which switches the ignition coil on and off, creating spark. Older distributors also contained mechanisms to vary the timing of the spark to match differing engine operating conditions. The ignition coil might be mounted within the distributor or nearby, and upon demand can create up to 40,000 volts of electricity.

The ignition coil’s output is directed to the upper portion of the distributor, which contains the rotor and distributor cap. As the rotor spins, it directs sparks to cylinder-specific terminals on the distributor cap, and spark plug wires complete the circuit to the spark plugs.

The potential for difficulties are many. Mechanical wear can cause mistiming of the spark, and the arduous delivery path allows many chances for resistance or escape along the way.

The 1980s brought many significant improvements to automotive-ignition systems. Points and condensers became a thing of the past, replaced by wear-resistant sensors and modules. Smart engine-control computers took over for mechanical spark advance mechanisms, and ultimately, the distributor began to go away, replaced by crankshaft sensors, coil packs and computers.

Early and some current distributorless ignition systems use one double-ended ignition coil for each pair of engine cylinders. Spark is delivered via conventional, well-insulated wires to one plug, goes through the cylinder head, across the mate cylinder’s plug backward and then home to the ignition coil. This method, known as waste spark, eliminates the distributor, cap and rotor, increasing performance and improving reliability.

More recent distributorless ignition systems might be of the coil-on-plug (COP) type. Individual ignition coils, mounted directly above each spark plug, eliminate the spark plug wires, improving performance and durability even further.

A COP ignition system requires no maintenance and allows greater control and monitoring of each cylinder’s performance. Its simplicity allows easy fault diagnosis, and in the rare event a problem should develop, the multiple coils and drive circuits offer greater protection against vehicle breakdown.

Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose.