5 Bad Spark Plug Symptoms | How to Know When You Need Replacing

The spark plug is one of the essential components of the combustion engine that helps produce efficient power. Whatever you do, the spark plug of your car must be kept clean of dirt, fuel, oil to keep it damage-free.

Bad Spark Plug Symptoms

Or else, a bad spark plug will undoubtedly affect the performance of the engine. There are specific symptoms that will tell you, your vehicle’s spark plug got issues and needs immediate attention.

5 Symptoms of Bad or Failing Spark Plugs can include:

  1. Affected fuel economy
  2. Decrease acceleration performance
  3. Poor and Hard starts
  4. Engine misfires
  5. Rough /Problematic idling

5 top Bad spark plug symptoms:

1. Affected fuel economy:

Bad spark plugs makes your engine work harder by not burning the fuel efficiently, which means they are using more fuel than required. Therefore, the gas mileage falls, and you will see yourself more on gas-stations.

2. Decrease acceleration performance:

The vehicle will struggle for proper acceleration with worn-out plugs. They are not capable of igniting fuel-air mixture into the combustion chambers and creating the spark necessary for acceleration.

3. Poor starts:

It’s very evident that if the engine’s spark plug doesn’t produce enough combustion to spark up the car, there will be hard starts. Faulty spark plugs might even lead your vehicle not to start at all if not fixed in time.

4. Engine misfires:

The engine makes some rattling noise, does not run smooth, and misfires frequently. Here, the sole cause is worn-out spark plugs.

5. Problematic idling:

Does your car vibrate now and then, or doesn’t it run smoothly while running? Well, that might be a symptom of bad spark plugs.

What are the costs of replacing your spark plugs?

The cost of replacing spark plugs varies on how any of them needs replacement. As spark plugs are very cheaply priced, replacing a few pieces won’t cost much, as they cost less than 10 dollars per piece.

On average, a person spends 10-100 dollars on spark plug replacement.

However, for replacing the spark plugs, you need to add on the servicing cost too, which might vary from 50-150 dollars depending on your area’s servicing cost.

But it will be a good idea to go for expert labor for the replacement as he will settle the matter once and for all without the need for re-replacing.

How to Replace Your Spark Plugs?

Replacing Your Spark Plugs

If you want to save the cost of replacement labor for your spark plugs, then you can do it at home by yourself by following some easy steps. You will also need some hand tools, new spark plugs, a spark plug socket, and dielectric grease.

The first step will be to ensure safety and precautions. Ensure the engine is not steaming hot and is in dry condition and read the car’s manual to ensure nothing wrong will happen if the system is dismantled for a certain time.

Now, remove all the interfering items there and install new plug wires.

Then remove the ignition coil on the plug, and screw open the old spark plugs. Place in the new spark plugs, and replace the coil on the plug.

Lastly, reconnect the battery and start your car’s engine.

How to maintain your spark plugs?

Maintain Your Spark Plugs

Maintaining your vehicle’s spark plugs is crucial as these are valuable assets.

The very first and primary step of maintenance is checking. Yes, checking your engine and its belongings within a schedule is essential.

This will help you figure out any issue as early as possible. The checking schedule should be as often as you use your car, mostly after every 24 hours of use because the spark plugs are supposed to get damaged over time, which is not anyone’s fault.

Now, to make sure the spark plugs live a little longer, you can occasionally clean them at home. Some amount of sediment or grime might be stuck into it, or fuel from the engine is dripping its surroundings.

If you see that, then take a simple wire cleaning brush or a spray-on spark plug cleaner to get rid of all the dirt. For stubborn deposits, you can use something sharp to scrape them off.

However, make sure never to use vinegar or other types of chemical cleaners for the plugs.

Lastly, replacing your worn out or bad plug/s are also part of maintenance. It will prevent the other plugs from damaging them too.

What happens when spark plugs go bad:

You get to see lots of distortions in your car’s overall performance when the spark plugs wear out. Some of the noticeable symptoms are jerking or shaking your car without any cause, rattling noise from the engine. And, you will face a hard time getting your car started.

Bad spark plug symptoms motorcycle:

For motorcycles, you will see the bad spark plug getting corroded, burnt, or broken. Moreover, the motorcycle’s performance will be hampered too. Such as, having idling, engine flooding and misfiring, are the common symptoms.

Symptoms of bad spark plug wires:

Symptoms Of Bad Spark Plug Wires

To start, your vehicle will face engine idling, hesitation, and surging if the spark plug wires go bad. As we know spark plug wires play an important role in many vehicle’s electrical systems, therefore anticipate that there are some bad spark plug wires symptoms.

And here are the 5 Bad spark plug wires symptoms –

  • Reduced Engine Power,
  • Engine misfire,
  • Hard starting,
  • Engine hesitation and rough idling, etc.

Can a bad spark plug wire cause misfire?

Yes, a bad and worn spark plug wire can cause a misfire. A loss of spark is another reason for which a cylinder often misfires. Especially in case of bad, worn, and damaged spark plugs, it is bound to misfire because of a loss of spark.

Bad spark plug wires symptoms for Motorcycle

Bad spark plug wires symptoms for Motorcycle are: Misfiring and backfiring issues, flooded engine, damaged spark plugs, powerful smelling gas, and gas will spray out of the exhaust.

Can bad spark plugs cause electrical problems?

The job of a spark plug is to wire transfer the electrical power from ignition system to engine spark plugs of a vehicle. When your spark plug will be in a good condition, this process will run smoothly. But if your spark plug is bad or damaged, then the whole process will have issues and your engine won’t work. Therefore, bad spark plugs can certainly cause electrical problems.

Can bad spark plugs cause a car not to start?

When you will have a good spark plug, then it will burn your fuel efficiently and keep your car engine running and kicking. But a bad spark plug will cause the engine not to start at all. Spark plug plays a vital role in keeping a car running and therefore it requires routine services and maintenance like fuel filters, motor oil, and air filter.

Can bad spark plugs cause check engine light?

Can Bad Spark Plugs Cause Check Engine Light

A bad spark plug can certainly cause your check engine light to come on and for this reason, your engine will start to misfire pretty soon. Your check engine light will start to pop on to indicate to you about a potential misfire. But when your spark plug will be a good one, then you won’t face this type of issue at all. Rather, your need not check your engine light to come on as well.

Bad spark plug sound

Describing the sound of a bad spark plug is not hard. As you can easily tell from your car’s vibrating and rattling noises, there must be something wrong with the engine. And, your guests won’t be wrong.

What causes bad spark plugs

Lack of maintenance and overlooking specific issues cause the spark plugs to go bad. Cars frequently overheat, not cleaning up buildup, and pre-ignition lets the plugs wear out soon. But you can always replace the bad ones.

How to tell if a spark plug is bad by looking at it

That’s very easy to tell just by looking at the plugs. You will see the plugs are rusting or fading, and they have a tanned grey tone all-over. Also, you will notice some fuel deposits on the insulator tip.

What does a bad spark plug look like

A bad spark plug looks burnt and rusted. It gets white blisters on the tip as a result of overheating. Also, you will see oil layers caked on it.

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Symptoms of faulty ignition leads

There are some specific symptoms of faulty ignition leads from which you can anticipate the issues in early stages. Those symptoms are as follows:

  1. Power will decrease as well as the fuel efficiency and acceleration.
  2. Engine performance problems will appear regularly.
  3. Engine light will come on to check things.
  4. Cables and wires will be damaged and worn out.
  5. You will find visible wear in your vehicle.


How do I know if my spark plugs need changing?

If your vehicle is showing unusual symptoms like shaking, jerking, rattling noise, difficulty in acceleration, then a significant chance of these have resulted from bad spark plugs. Then when you know, your spark plugs need to get replaced.

How long can you drive with bad spark plugs?

Depending on the amount your spark plugs got bad, you can decide on that. However, for an estimate, you can drive your car 80,000 miles maximum with the least damage. But that drive is not going to be smooth!

What does a bad spark plug look like?

A bad spark plug looks burnt and corroded away. They get white blisters on the tip as a result of overheating. Also, you will see oil layers caked on it.

Can spark plugs suddenly go bad?

It’s mostly not your fault if your spark plugs suddenly go bad. Yes, they can suddenly go bad, but won’t go bad all at once. They will start by showing gradual symptoms that must be paid attention to.

Do spark plugs smell when going bad?

Yes, they release a powerful gasoline smell while going bad. This is mainly due to the unused gasoline inside the chamber as the worn-out plugs couldn’t utilize it.

Can a spark plug just die?

Fortunately, no. Spark plug dies slowly and not all of a sudden. As mentioned before, they show dying symptoms, which, if not paid attention to and replaced, will cause them to stop working.


Now that you know a lot about bad spark plugs and its symptoms, it’s high time you start paying attention to them. People often forget that they are one of the essentials of a vehicle and need care.

Therefore, prevent them from going bad and increase their longevity by starting a regular maintenance routine. When the spark plugs are satisfactory, your journey will be fun, smooth and safe!