6 Commons Symptoms of Bad Spark Plug Wires

Damaged spark plug wires reduce the efficiency and functionality of spark plugs. The starting of the engine mostly depends on the healthy spark plugs. When the wires are malfunctioning, the plugs will not ignite for not getting the necessary electrical voltage from the ignition coil. You should learn about the symptoms of bad spark plug wires, so you can fix them and make sure about the ignition of the spark plugs.

What Are the Symptoms of Bad Spark Plug Wires?

In the electrical system of a motor vehicle, spark plug wires play a critical role. They transfer electrical power from the ignition system to the spark plugs, so the engine gets enough sparks to kick off. When the wires fail, a number of engine-related problems will arise, including the following:

Rough Engine Idling

The engine spark plugs get the required electrical power through the plug wires. This electrical current helps with the ignition of the air-fuel mixture in the engine’s combustion chamber. So, bad wires mean the ignition won’t happen properly, causing rough engine idling.

Hard Starts

If you struggle to start the engine, it could either be a problematic battery or a bad spark plug wire. In fact, damaged wires can play a part in the parasitic drainage of the battery, which affects the engine directly. You should check the spark plugs and the wires if the battery turns out to be fine.

symptoms of bad spark plug wires
Bad wires make it harder for the engine to start. (Source: Stuorguk~enwikibooks / Wikimedia Commons)

Engine Misfiring

Erratic or incomplete combustion in the engine’s chamber is the main reason for engine misfiring. As spark plugs create the necessary sparks for that combustion, bad wires mean they cannot do that task properly. There could be brief periods of regular and irregular flow of current, which is not adequate for a full combustion. For this reason, the engine will misfire every time you try to start it by turning the ignition key.

Engine Hesitation

When the wires degrade or develop cracks, they supply irregular electrical conduction to the spark plugs. This condition causes engine hesitation at the time of acceleration. It happens due to the disruption of the regular flow of electrical power from the battery to the plugs. An abnormal fuel flow can create the same problem too.


Engine Surging

When there are cracks in the outside insulation of the wires, the electricity will face a significant resistance when passing through them. For this reason, the electrical current could be completely stopped or experience brief spurts when transmitted to the spark plugs. This phenomenon causes engine surging, which is not good for the overall health of the vehicle.

Poor Engine Power

All the symptoms of bad spark plug wires ultimately result in an underperforming engine. Since the air-fuel mixture doesn’t combust properly due to bad wires, the engine cannot function at its full power. Cracked damaged wires impede the regular flow of electrical current to the spark plugs, causing a massive loss of engine power.