Signs And Symptoms of Bad Spark Plug Wires

All cars have many different ignition system components, minor differences due to systems and models. For example, new cars have ignition coils while others have spark plug wires. These ignition systems convey the sparks from the ignition to the spark plug to start the vehicle.  

These wires have low resistance and can withstand the high voltage of the ignition system. If they do not work efficiently, the engine performance does not receive adequate power. Here are some of the signs of bad spark plug wires that you must know. 

Signs And Symptoms of Bad Spark Plug Wires

1. Difficult to start the car

The car may take longer to start due to other reasons like battery, but the most common cause is the damaged wire of the spark plug. These wires will drain the battery and may need to be replaced. 

2. Surging in engine

This is another sign that the spark plug cables are faulty and usually occur due to insulation damage.

The electricity may face more resistance, and the engine may receive sudden spurts of power alternating with no power at all. Replacing the damaged cables is the ideal solution. 

3. Engine idling is rough

When the car is stationary, it must have a smooth idle. But when the spark plug wires are damaged, the ignition is not smooth, leading to uneven and rough idling. However, check for other reasons too before changing the cables. 

3. Delayed and stalling vehicle movement

Some kind of hesitating movement of the car may result from irregular power to the engine again due to faulty spark plug cables. This is prominent during acceleration too. Wires may be broken inside the insulation, and electricity is not transmitted properly.  

4. Misfiring engine

Spark plug wires convey sparks in a predetermined order, but a faulty mechanism may disorganize them. This irregular flow of current alternating between normal and more or less flow damages the engine.

This kind of irregular power supply will reduce the efficiency of the process of combustion of fuel in the engine. If things go this way, you must opt to change the cables. 

5. Acceleration happens slowly, and mileage is also reduced

Bad spark plug wires may lead to a slow acceleration in the vehicle. The car slowly loses its power as it uses more power and more fuel with each misfire of the spark plugs. The mileage of the car also reduces due to the same reason. 

6. Engine power reduces 

The electricity that passes to the engine is erratic with faulty spark plug wires and may fluctuate too much. The entire combustion process and thereby the engine’s power may be damaged, leading to loss of power. It would be best to replace the cables to restore the regular current flow to the engine. 

7. Damage is visible

This is the clearest symptom of cable damage when you see signs of wear and tear on the spark plug cables. The insulation may be cut or eroded, or some wire may be torn or cut. The cracks may happen with time, and you must periodically check these cables’ state while servicing the car. 

8. Engine sounds 

Knocking sounds from the engine indicate damaged spark plug wires. Because this at times the engine or the complete transmission system might get damaged. The sounds occur due to incomplete combustion of fuel and delayed power to the pistons due to erratic transmission of power through the cables. 

9. Car sensors warning

Today cars have a warning system that can detect these faults in the engine and flash a light on the dashboard. The light telling you to check the engine indicates potential problems with the engine components, and a faulty spark plug cable may be one of them. 

Test The Spark Plug Wires

The signs mentioned here indicate that the spark plug wires are damaged, and you must conduct some tests to confirm the same. You must have specific tools like pliers, screwdrivers, an Ohmmeter, etc. to test the spark plug wires. 

First, check the cables for any external damage, including corrosion, after cleaning them of dust. You must disconnect the spark plug cables one by one and test them carefully before reconnecting. This test is done using an analog or Ohmmeter and checks the resistance of these cables. 

Check their connections and sequences. It is essential to match the cables correctly in the order as wrong connections may also lead to misfires and surging of power to the engine, which may cost you a lot more. 

You must check for electrical leaks by examining the wires after turning on the engine. Stay away and do not touch any wire when the engine is on. Mechanics can perform a spray bottle check, but they better do it, and we should avoid spraying water when the engine is on. 

You can replace the cables and reconnect to put everything is in order. Start with the shortest wires and go to the longest ones. You can also opt to clean or change the spark plug simultaneously.  

Some Tips For Maintaining The Spark Plug Cables

Car manufacturers may recommend different intervals to change the spark plug cables. But it is essential to check their competency frequently to remain in good shape. 

It is also critical to change these cables if you see any of the above-mentioned symptoms, as ignoring them will lead to more complex and more expensive faults in the engine. The driving speed to mileage may be affected if the spark plug cable malfunction.  


Changing spark plugs wires may not improve the car’s performance as such as it is an essential component for its optimum performance. But if the wires are damaged, the performance will deteriorate over time.

The performance will be hampered considerably with incorrect power to the engine and related issues. Replacing the cables is very easy and can be done by yourself or take the vehicle to a mechanic.

If you notice any of the symptoms mentioned here, do not wait for the system to deteriorate, and check the cables first. These are the lifelines of the car engine and need immediate attention.

Liam Dare

As CEO of, my passion for the automotive world motivates me to build online businesses that provide information and entertainment to users. I am proud to contribute in a positive way to the automotive community.