Bad Spark Plug Wires Symptoms and How to Change It in Your Car

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Car engines run on fuel. Any responsible person who learns how to drive has to understand how the car engine works. They should be able to tell what’s normal or abnormal and how to correct it. The ignition system in cars is a common site of malfunction that every driver should understand clearly. One should be able to tell when the system is working correctly versus when it is failing. They should also be able to predict the level of wear and tear and replace the wearing out parts accordingly.

Spark Plug Wires are also known as the ignition cables. They carry the ignition spark from the engine’s coil to the spark plugs. As such, they are made of material strong enough to withstand the horrendous conditions around the engine. Understanding bad spark plug wires symptoms and how to change them will help you a great deal.

What Do Spark Plug Wires Do?

the spark plug wires in car
The spark plug wires’ work is to conduct that high voltage from the ignition cable to the spark plug.

The spark required to ignite the fuel mixture in the engine is generated from a high voltage. The high voltage must be conducted from the ignition coil to the spark plug, where two electrodes facilitate the spark from the high potential difference. The spark plug wires’ work is to conduct that high voltage from the ignition cable to the spark plug. Conducting such a voltage requires a material with low resistance and increased durability. These are qualities that dictate the manufacture of spark plug wires. However, wear and tear is a common occurrence due to the high voltage and low resistance.

Symptoms of Sparking Plug Wires

Based on ignition cables’ job, one of their malfunctions manifestations is a deficiency in the engine’s performance. Faulty ignition cables resulted in failed ignition and failed combustion of the fuel within the engine. As a result, the engine will either reduce its power output, fail to accelerate or reduce its fuel efficiency. These are common bad ignition cable symptoms that can help you diagnose the problem before calling a mechanic. In severe spark plug wire malfunction, the engine can even stop altogether.

In most vehicles, a bad spark plug wire will be indicated by the ‘check the engine light‘ on the vehicle’s dashboard. Be thoughtful enough not to ignore that light. Occasional checking of the ignition cables can show wearing out cables, meaning it is time you got them changed.

How to Change Spark Plug Wires in Your Car 

Changing ignition cables is an easy but very cautious task that needs proper concentration. You can safely perform it on your car, but you have to be careful not to miss any steps.

Step 1: Removing the Old Ignition Cables

The boots of the wires are the ones attached to the spark plugs or the distributor caps. To remove the cable from the plug or the distributor cap, you rotate the boot to loosen it. After loosening, pull the boot from the plug. Avoid pulling on the cable itself at all costs – that’s likely to break the connection. Removing the ignition cables should be systematic, from the longest to the shortest. Once you remove a cable, replace it before removing the next one to avoid mixing them up.

Step 2: Replacing the Ignition Cables

Match the length of the new set of ignition cables to the old set as you remove each one. Start with the longest cable and finish with the shortest. Then fix the ends of the cable onto the module first, then onto the plug. Rolling out the boot’s edge can help remove air and allow the wire to fit correctly. Hold the boot and push the wire in firmly until you hear a click. You can test if the wire is fixed well by applying a firm pull.

Replace each wire after removing it to avoid a mix-up, resulting in a misfiring cylinder and an engine malfunction.

How Often Do You Need to Change Spark Plug Wires?

It’s safest to change your ignition cables before they wear out. That avoids the doubts of being caught off-guard by an engine malfunction because of wearing out ignition cables. The estimated mileage is usually about 60,000 to 100,000 miles. The car manufacturer always explains this in the manual.


Does Changing Spark Plug Wires Improve Performance?

Yes, they do. New ignition cables are more efficient and better at conduction than old ignition cables. Therefore, a new set of ignition cables boosts the cylinder’s firing potential and increases the engine’s output, hence improving the performance. Robust and durable ignition cables are recommended as they last longer.

How Much Does It Cost to Change Spark Plugs and Wires?

Spark plugs are comparatively cheap, going for about $16 – $100. Depending on the model of the car, spark plugs are easily accessible and affordable. Some are even negotiable, and the installation price can be bargained with the mechanic. The labor cost is usually as low as $40.

How Long Do Spark Plugs and Wires Last?

As with vehicles, the life span of the parts is dependent on mileage. The estimated duration for ignition cables is about 60,000 miles. You can change your ignition cables before then if the boots appear worn out.

Are Spark Plug Wires All The Same?

No, they are not. Although the ignition cables’ structure may appear similar, the quality of material used determines the longevity of service and efficiency. Some materials are better at conducting the electric current than others, hence the difference.


Engine malfunctions are a nuisance to all the drivers. Given a chance, we would do all we can to avoid enduring one, especially if you are in a rush. Bad ignition cables are a common source of engine malfunction. They need to be replaced accordingly and in time. Taking care to not mix up during replacements is a critical issue. A new set of ignition cables is a significant boost to your engine’s performance.

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