Bad Spark Plug Wires Symptoms – 9 Signs That You Should Know

Spark plugs or ignition cables are components that are vital to your vehicle running. While most newer vehicles utilize ignition coils, many older models still use spark plug cables. In this article, we’ll discuss 9 bad signs that indicate that you’ve got bad spark plug wires.

How does all of this work? 

To put it simply, your car’s ignition system works by creating sparks at intervals that are premeditated. They do this to ignite the fuel/air mixture inside your engine’s fuel combustion chamber. With all that said, your spark plug wire’s primary job is to transmit the spark from the ignition coil or distributor to the spark plugs themselves.

Spark plug wires are manufactured to withstand heavy wear and tear for many years. However, like all engine components, they’re subject to failure. When that occurs, there are 9 symptoms that you should look out for to make sure that your car continues to run at peak performance.

9 Signs of Bad Spark Plug Wires

Bad Spark Plug

Typically, bad spark plug wires exhibit 9 symptoms that’ll let you indicate that it’s time to visit a mechanic. Below are these symptoms explained in-depth:

Diminished Engine Performance

An engine could perform noticeably worse when its spark plug wires are in bad condition. 

You see, the spark plug of an engine must remain undeteriorated to guarantee a proper combustion cycle. Now with any deterioration, it is certain that your engine will suffer from a noticeable reduction in power.

Your Engine Is Hesitating

Once your engine’s ignition degrades and develops small cracks, an irregular spark will be transferred to your spark plug wires. When that happens, your engine will hesitate, especially when it is being started up.

Rough Idling

Many types of mechanical issues can bring about rough idling. Needless to say, the only way to determine if your spark plug wires are the reason behind your engine’s rough idling is via the assistance of your local qualified auto technician.

Sudden Engine Surging

Leaks and cracks within the ignition head’s insulation shall cause a brief or complete loss of electrical transmission to your spark plug wires. As a result, your engine will surge.

Hard Starting

Hard starting is an issue that many engines suffer from. The reason for it can range from everything from a faulty battery to bad spark plug wires. As such, you should inspect your spark plugs if your vehicle’s engine ever hard starts.

Vehicle’s Engine Is Misfiring

An engine misfire is the nightmare of any vehicle owner or driver. Sadly though, this issue is an inevitable one that cannot be avoided if your car isn’t regularly inspected by a mechanic. 

For those who do not know, an engine misfire is caused by internal combustion that is incomplete or erratic. 

Because spark plugs are specifically made to create sparks at predetermined intervals, bad spark plug wires won’t be able to transmit the required spark, and therefore, cause your vehicle’s engine to misfire.

Your Car’s Indicator Is Lighting Up

Nearly all modern vehicles are built with many sensors that report your engine’s conditions to your car’s ECU. When a problem with your engine’s spark plug wires occurs, then your car’s problem indicator may light up.

Reduced Gasoline Mileage

If your car’s bad spark plug wires fail, then your engine’s combustion process might negatively get affected. Consequently, your vehicle will be forced to consume more gasoline, which is terrible news given today’s fuel prices.

Knocking Noises

Bad spark plug wires cause delayed or incomplete combustions in your engine. Due to that, you’ll hear knocking noises that can be rather annoying. Also, these knocking noises can cause serious damage to your engine so it would be a good idea for you to have your vehicle checked immediately.

How to Test Spark Plug Wires?

How to Test Spark Plug Wires?

It can be difficult to diagnose if your engine has bad spark plug wires because it shares similar symptoms with many other problematic components. If ever you experience the problems above, then it would be an excellent idea to test your engine’s spark plug wires.

These tools will be necessary to test your spark plug wires by yourself:

  1. Owner’s manual
  2. Analog meter or Ohm
  3. Cleaning rags
  4. A 30-60 cm jumper wire
  5. Tape measure
  6. Spray bottle filled with water
  7. Standard-sized screwdriver
  8. Spark plug wire pliers (optional)

Always test your ignition leads one by one. Disconnect the spark plug wires one at a time and then reconnect them following each test. When that’s done, it will be possible to avoid mixing your cables and accidentally causing your vehicle’s engine to misfire. Be sure to create a list and make sure that you follow your engine’s firing order so that it’ll continue to run smoothly.

Step 1: Perform A Visual Inspection

Before even touching your car’s engine, you should first do a visual inspection to determine if it doesn’t have any obvious external problems. After conducting your inspection and still experiencing engine problems, it’s time to head over to your local mechanic.

Step 2: Check For Electrical Leaks By Turning On Your Engine

Your first course of action should be to start your engine and then examine each spark plug wire very carefully. Snapping noises around the wires are telltale signs of an electrical leak. Under any circumstance should you touch the spark wires since you may end up hurting yourself.

Step 3: Do A Spray Bottle Test

To check your spark plug wires using water, you’ll need to be in a place wherein you can switch your lights on and off. Why? Because detecting electrical leaks can be hard if you’re in a well-lit garage.

With all that said, get your spray bottle and then start your vehicle. After that, spray water on the distributor to check for arcing as well as electrical leaks. Next up, spray water on your ignition leads all the way down to your spark plug areas to check for any electrical leaks and arcing.

Step 4: Do An Ignition Lead Resistance Test

Go ahead and check the resistance of each of your engine’s spark plugs. 

Use an analog meter or an Ohm and don’t forget to check the spark plugs one at a time. Moreover, make sure that you return them to their appropriate place if they check out okay. 

Step 5: Cross-Check Your Spark Plug’s Wire Connections

Open up your vehicle’s owner’s manual and then check if the lead wire is connected properly. 

It is very important to remember that improper routing causes wires to relax on hot components and drain power. Also, prolonged wire contact with hot engine components might cause your engine to have permanent damage.

What Causes Spark Plug Wires to go Bad?

So what exactly causes spark plug wires to go bad? Like all other engine components, they are constantly subject to wear and tear. Be that as it may, the major reasons why spark plug wires get faulty are because of carbon buildup, oil leakage, and improperly connected spark plugs.

When Do I Change My Spark plugs?

When Do I Change My Spark plugs?

When it comes to anything related to your automobile, it’s better to be safe than sorry. Since the spark plugs of your car are so important to its ability to function, you must regularly perform checks. That way, you’ll get to avoid spending exorbitantly on car maintenance costs.

For starters, check your car’s manual and your odometer’s reading. These two things will let you know if it’s time to head to the mechanic for a regular checkup. Don’t skip this as you run the risk of causing permanent damage to your car’s engine, which might need overhauling.

Another way to know when it’s time to change your engine’s spark plug wires is when you begin to experience the 9 symptoms that were aforementioned earlier. Needless to say, unless you’re a qualified mechanic, you’ll need to visit your local auto shop to truly know whether your engine spark plug wires need a replacement.

How to Change Spark Plug Wires?

How to Change Spark Plug Wires?

So you’ve got some DIY technical know-how and wish to change your spark plug wires without the help of a mechanic. To do this, simply follow the steps mentioned below:

Step 1: Make A Record Of Your Wire’s Locations

Don’t do anything until you have taken pictures of the original locations of your wires. That way, upon putting them back, they’ll not cross-fire or interfere with your car’s other sensors. Aside from that, it shall also be way easier for you to return everything once you are done.

Step 2: Arrange Your Wires

Get your new spark plug wire, uncoil it, and then arrange it by length. When visiting your auto parts store, it’s highly recommended that you purchase a premium set of wires. By doing this, you’ll be getting much more value for your money.

Step 3: Get Rid Of The Boot

The next thing you should do is make the appropriate investment and get yourself a spark plug wire puller tool. Believe me, doing this will save you a lot of time as well as energy when removing your old spark plug wires that decreases your vehicle’s performance.

Step 4: Apply Grease

It’s not uncommon for automobile manufacturers to precoat your engine’s plug and its coil along with its distributor boots with dielectric silicone grease. How come? The grease adds lubrication, which prevents the boots from adhering to the plug or coil/distributor. Aside from that, it provides insulation from voltage traveling down the boot.

Now if your set is uncoated, make sure to apply a tiny amount of silicone grease as well as to run a bead within each boot. Moreover, put some grease on the plug as well as the coil and distributor of each plug. After that, simply route the wire, then press until you feel a click.

Step 5: Conduct Wire Replacement

Take one the spark plug wires out one at a time. Your next move should be to accordingly match them to the replacement wire of the same length then conduct wire replacement.


Can a bad spark plug wire cause the car not to start?

Yes. A bad spark plug wire can absolutely prevent your automobile from starting. For those who don’t know, a spark plug wire’s primary job is to provide the needed spark from the ignition coils and distributor to the spark plugs. 

When a spark plug wire becomes compromised, it tends to supply an insufficient spark that can’t ignite the fuel/air mixture in your car’s engine combustion chamber. As a result, your automobile goes through rough idling, or worse, ceases to start at all.

How often do you have to change your spark plug wires?

The answer to this question generally depends on the manufacturer of your vehicle. With all that being said, a brand new engine’s spark plug wires should work flawlessly for at least 60,000 miles. 

Needless to say, a lot of factors can play into why you might need to change your automobile’s spark plug wire much earlier.

Does changing spark plug wires improve performance?

Changing your spark plug wire will improve your car’s performance if your old spark plug wires were already causing problems such as hard starts. However, if you want to make your car run faster, then you are out of luck because a spark plug wire upgrade won’t improve performance.

Wrapping Everything Up

It can be hard for anyone who isn’t good with engines to determine the reason why their vehicle is running badly. One of the culprits that may be behind your car’s diminished performance is its spark plug wires that may have become degraded. 9 signs will tell you that your car’s spark plug wires have gone bad. By reading this guide, you shall know all about them.

Furthermore, this guide will teach you how to change bad spark plug wire by yourself. That way, you won’t have to pay an expensive visit to your local mechanic. Last but not least, it answers some of the most common questions people have about spark plug wires that have gone bad.

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