Spark Plug Wires

Spark Plug Wires

Spark plug wires are transport arteries of a vehicle, delivering high voltage generated by its ignition coil to the spark plugs. While most modern vehicles do not use spark plug wires, there are still a lot of older vehicles equipped with spark plug wires. Depending on the design of a vehicle, its spark plug wires connect each spark plug with either a distributor cap or ignition module. Based on this, ignition systems with a distributor cap are called distributor ignition systems, while the others are named distributor-less ignition systems. Let’s check both of them.

Distributor ignition systems

It is the oldest ignition system design found in a vehicle. The ignition coil uses the battery’s low voltage to generate high voltage needed to create sparks, and then sends it to the distributor via a properly insulated wire. As the distributor’s rotor turns, it supplies high voltage to each spark plug via spark plug wires.

Distributor-less ignition systems

As their name clearly says, distributor-less ignition systems do not have a distributor to deliver high voltage to spark plugs. Instead, they rely on several ignition coil packs, each of which usually provides voltage to two spark plugs. This ignition system design is considered to be more efficient compared to its distributor counterpart, however, it is also not used today since most modern engines feature an individual coil pack on the top of each spark plug.

Just like spark plugs and many other engine parts, spark plug wires are prone to wear and tear over time. Besides, they can get damaged, causing a variety of problems:

Poor performance and acceleration

A damaged or high-resistance spark plug wire can prevent the spark plug from firing, resulting in incomplete combustion and, therefore, misfires. The latter will reduce your performance and worsen your acceleration.

The check engine light will come on

Misfires caused by bad spark plug wires will increase your vehicle’s emissions. Since your control unit constantly monitors them while the engine is running, it will turn on the check engine light once the problem is found.

High emissions 

As it described above, bad spark plug wires may lead to increased emissions. This means you will not be able to pass a state emissions test.

Increased fuel consumption

Bad spark plug wires are synonymous with incomplete combustion. You’ll have to spend more money at the pump than it used to be. 

How can I fix bad spark plug wires?

The only way to fix problems caused by bad spark plug wires is to replace them with new ones. But before replacing the wires, a qualified mechanic should check them with a scan tool or oscilloscope. It is also a good idea to let the mechanic replace the spark plug wires to prevent occasional damage to spark plugs or other engine parts.

Many spark plug wires are designed to last from 60000 to 100000 miles. However, they may fail faster if they get physical damage, or contact oil or coolant.  

If you feel comfortable replacing spark plug wires, you can do the trick yourself. Just be sure to use OE-quality replacement parts and follow the manufacturer’s replacement recommendations.