What Causes Spark Plug Wires to Go Bad? (Explained!)

Spark plugs are critical parts of an engine, so every driver should always maintain them. However, a damaged or failing spark plug entails many risks and opens many potential issues. For this reason, you need to understand what causes the damages and how you should deal with such. So, you may ask: 

What causes spark plug wires to go bad? Spark plug wires get damage due to many things that also damage the spark plugs per se. The four major causes are oil leakage, overheating, carbon buildup, and improper gap on spark plugs. It’s essential to address and solve each one to maintain the spark plug wires.

Spark plugs and their wires are essential parts of every gas-powered vehicle. Without these parts, nothing will provide a spark to the ignition when starting an engine. For this reason, you need to understand the causes of damage and do your best to address and prevent such.

In this article, you’ll see an in-depth take on the four major causes of damage to spark plug wires and the spark plugs per se. This way, you can know how to prevent them and solve the issue if it ever occurs.

Without further ado, let’s get into it!

What Causes Spark Plug Wires to Go Bad

Reasons Why Spark Plug Wires Go Bad

Here are the four significant reasons why spark plug wires go bad. In general, it’s also the four primary reasons why spark plugs get damaged easily. 

Please take a look at each one to understand how it can affect the performance of your spark plug and the wires attached to them.


The overheating of the spark plug tip repeatedly might cause the plug to break eventually. Pre-ignition and a faulty cooling system are two common causes of overheating.

Pre-ignition can cause the spark plugs to fail due to excessive heat in the combustion chamber. 

Furthermore, if the ventilation system isn’t working correctly, the motor and spark plugs might overheat. Such overheating can cause the electrode and wire of the spark plug to burn out more quickly.

Oil lead from the combustion chamber

The passage of engine oil into the combustion chamber is a primary source of spark plug issues. If oil seeps into the combustion chamber, the spark plug’s tip might get greasy and filthy, causing it to fail prematurely.

If your car starts to burn oil, it might signify that your spark plugs are broken, which is very common in older cars. Thus, you can say that the spark plugs in such models have a shorter lifespan.

Improper Spark Plug Gap

To achieve optimal engine performance, you need to precisely adjust the distance between the center and side electrodes of the spark plug.

The proper gap guarantees that the arcing takes place at the appropriate voltage to burn the gasoline and create the ignition that allows the engine to function.

Suppose you don’t adjust the gap appropriately. In that case, the spark plug tip may be prone to additional stress, causing it to deteriorate and burn out early.

Carbon Buildup

A carbon-fouled spark plug has black, dried soot on the wires and insulation tip. Carbon accumulation shortens the longevity of a spark plug, resulting in difficult starts, reduced speed, engine failures, and the appearance of the check engine light.

A filthy air filter, prolonged running at low speeds, too strong of a fuel/air combination, dirty fuel nozzles, or sitting idle your vehicle for too long are all factors of a carbon-fouled spark plug.

bad spark plugs

How Do I Know If My Spark Plug Wires Are Bad?

The best way to know if your spark plug wires are bad or failing is by looking out for the symptoms and effects of such. Thus, here are some of the things to look out for so you can check if the spark plug wires are alright or if they already need maintenance.

Symptoms of bad spark plug wires

Below are three significant symptoms you can see on your car if you have bad or failing spark plug wires:

Damage due to excessive vibration

Excessive engine vibration can lead the electrical system at the spark plug to weaken over time. As a result, the voltage needed to ignite the spark plug rises. As a result, potentially damaging the ignition coil and spark plug wires.

Damage due to excessive heat

The heat from the engine might cause wire insulation and boots to burn. In addition, the correct seating and functioning of spark plug wires might be hampered by a damaged boot. 

Broken wire wrapping might cause electricity to go to the ground instead of crossing the space at the spark plug base.

Damage due to excessive abrasives

When spark plug wires brush against engine components, exceptionally sharp edges, the coating tears and breaks itself. When it happens, electricity may drop to the base rather than approach the spark plug.

Effects of bad spark plug wires

When you have bad or failing spark plug wires, you can suffer from the adverse effects they entail. Thus, you can know you have a bad spark plug wire if you experience any of the following problems:

  • Poor performance and acceleration
  • Poor fuel efficiency and reduced fuel mileage
  • Rough and frequent idling
  • Engine dying and misfires
  • Difficult engine startups

As a general rule of thumb, contact your technician to see any of these signs of a failed spark plug. They will be able to identify if a faulty spark plug is the root of your problem.


In a nutshell, spark plug wires wear and break out due to various factors that cause spark plug damage. Oil leakage, overheating, carbon buildup, and incorrect spark plug gap are the four main reasons. Therefore, to keep the spark plug wires in good shape, it’s critical to address and fix each one.

You can see that the significant causes of spark plug wire damage are also the same as the causes of damage to the spark plugs themselves. Thus, you can say that maintaining the spark plugs is also maintaining the wires attached to them.

In the end, it’s essential to have these parts fixed. If left unchecked, it could lead you to significant issues that would cost more than having it repaired soon.

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Image credits – Canva

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My name is Hank, and I've been in the automotive industry for 27 years. I've been working in my own auto repair shop for the last 13 years, and now I want to help you here, on my blog. Let me know if you have any questions. Read more