Home Diagnosis and TroubleshootingEngine Problems Bad Spark Plug Symptoms – Causes And How To Fix It?

Bad Spark Plug Symptoms – Causes And How To Fix It?

by Jordan Harris
Bad Spark Plug Symptoms

Have you noticed that your engine isn’t functioning as it should and that the check engine light appears on your dashboard from time to time? Bad spark plug symptoms could be to blame. Spark plugs are a critical component of the combustion process. Their role is to combust the mixture of fuel and air in the engine for ignition to occur, and for power to be created.

They accomplish this by utilizing high voltage current from the ignition coils to bridge the gap between the electrodes and reach the fuel mixture for ignition. Like other components that need to be replaced on a regular basis, Spark plugs begin to fail irregularly as they approach the end of their service life.

In that situation, they may not be able to perform as well as previously, resulting in misfires, idle problems, and hesitation, among other bad spark plug symptoms caused by an inefficient combustion process. We’ll address your question here: what are the bad spark plug symptoms, and how often should they be replaced? Once you have all of the facts about this problem, you will be able to make changes as needed without inflicting any harm.

What Exactly Are Spark Plugs?

A spark plug is a device used to transmit electricity to the combustion chamber of a spark-ignited engine. These devices deliver the current from an igniting chamber. As a result of this procedure, the compressed fuel and air mixture is ignited by an electric spark. At the same time, the combustion pressure within the engine is maintained, allowing the engine to function effectively.

When purchasing one, you should think about the wrench’s size, heat range, number, and torque. There are a few more factors to consider when utilizing it, such as the frequency with which it should be replaced and when.

Bad Spark Plug Symptoms

These bad spark plug symptoms will indicate if you have a faulty spark plug or not.

1. Acceleration Is Slow Owing To Bad Spark Plugs

A malfunction with the ignition system is the most prevalent bad spark plug symptom for the poor acceleration in most automobiles. The problem could be a broken sensor in today’s sophisticated engines. Several sensors inform the onboard computer and ignition system when to transmit electric pulses to fire the spark plug.

On the other hand, a worn-out spark plug can be the cause of the problem. A spark plug comprises components that combine to create a spark that is hot enough to ignite the air-fuel mixture.

When certain materials wear out, the efficacy of the spark plug is reduced, which can significantly reduce vehicle acceleration. A broken spark plug that has to be replaced could cause your car to operate sluggishly or not accelerate as rapidly as it used to. However, you should get your vehicle inspected by a professional because this problem could be caused by a variety of other issues, such as blocked or filthy fuel injectors or problems with oxygen sensors.

2. Trouble In Turning Over

This is one of the few indications that will make you spend the entire day looking for the missing link in your automobile. When it comes to starting an engine, a good spark is crucial. It aids in igniting the cold fuel mixture and the start-up of the vehicle’s overall operating system. Your vehicle will probably have a hard time turning over if your spark plugs are worn out when they can’t provide a sufficient spark.

This is caused by the components of the spark plugs wearing out over time. The space between the center electrode and the ground electrode, the state of ceramic insulators, and tip erosion are all factors that affect the ignition capability of spark plugs. When the spark plugs have worn out a lot, the car may not be able to run at all.

3. Hesitations Due To Bad Spark Plugs

Hesitation when accelerating is another common bad spark plug symptom. When spark plugs are unable to produce sufficient spark, the increased fuel injection may not be fully utilized, causing ignition timing to be thrown off.

Because of the erratic combustion, an irregular ignition of the fuel mixture is bound to cause hesitation. Spark plugs have been discovered to have an effect on acceleration from a startup in several circumstances.

4. Reduced Fuel Economy

According to a study done by the National Institute for Automotive Service Excellence, wearing out spark plugs can reduce fuel economy by up to 30%. That’s a lot of money when you consider how much it would cost to replace them simply. Another thing to keep in mind is that spark plugs do not affect gas mileage. You may receive poor mileage from worn-out spark plugs, but switching to higher-quality spark plugs will not affect the engine performance.

Worn-out spark plugs reduce gas mileage by wasting fuel since the weak spark cannot fully ignite and utilize the fuel combination. They eventually dispose of the fuel by sending it through the exhaust. If your fuel efficiency gradually improves, it may be time to replace your spark plugs.

5. Rugged Idling Due To Bad Spark Plugs

If your vehicle’s engine is rough or noisy when it’s idling, the fault is most likely with the ignition system. Heavy rumbling when waiting at a stoplight or in a drive-thru may signal that your vehicle is ready for service. The spark plugs could be a problem, but they could also be something else like the ignition coils.

Examine the system to see whether the spark plugs, ignition coils, or wires need to be replaced. If you don’t diagnose the problem first, you’ll waste time and money.

6. Difficult To Start Thanks To Bad Spark Plugs

If you’re having difficulties starting your car, it could be due to worn spark plugs. As previously stated, an engine’s ignition system is made up of numerous different components that must work together to perform efficiently. It’s a good idea to contact a trained mechanic if you’re having trouble starting your car, truck, or SUV at the first sign of trouble.

Regardless of the problem, you may need new spark plugs when your current ones wear out. Maintaining your spark plugs regularly will help you extend the life of your engine by hundreds of thousands of miles.

7. Misfiring Engine Because Of Bad Spark Plugs

Engine misfires are another bad spark plug symptoms that could indicate that your spark plugs are worn out. An engine misfire most often due to incorrect combustion, which a variety of factors can cause. Spark plugs can undoubtedly be one of the causes of the fuel mixture not being properly ignited.

When the fuel mixture reaches the ignition point, a powerful strike is required to ignite the mixture and force the piston down to finish the process. However, if your spark plugs have gone poor, they will be unable to ignite the mixture with sufficient force, resulting in incomplete combustion.

8. Performance Issues Caused By Bad Spark Plugs

Another common bad spark plug symptom is decreased engine performance caused by improper combustion. Various ordinary drivability areas that would have been seamless may provide unpleasant experiences such as difficult acceleration, problems shifting, and harsh idling with a diminished spark capacity.

Bad Spark Plug Symptoms

The efficient running of the vehicle as a whole suffers when the spark plugs are unable to deliver the correct quantity of power. They cannot ignite the fuel mixture effectively, resulting in a significant loss of power. Surprisingly, sluggish performance can also be caused by reduced fuel injection, as the vehicle can run in a lean condition.

9. Lean Condition Due To Bad Spark Plugs

The spark plugs have no effect on the fuel mixture on their own. They’re simply required to ignite the fuel mixture and burn it. However, when spark plugs fail, they might cause a strange situation in which they deceive current car oxygen sensors, causing a lean condition.

Unburnt fuel is one of the most common signs of defective spark plugs. This is produced by incomplete combustion rather than a rich state. Still, because the gasoline is being dumped in the exhaust, the O2 sensor may believe it is so and compensate by withdrawing fuel from the mix, resulting in a lean condition.

However, because the O2 sensors take time to attain operational temperatures and communicate the essential information, you may not immediately detect the symptoms of a lean fuel mixture.

10. Knocking Inside The Engine

Engine knocking is a severe form of engine misfiring. Engine knocking is one of the bad spark plug symptoms, and this banging is the traditional bad spark plug sound you’ve probably heard.

When the normal knocking sound becomes audible, you should be concerned since the potential of mechanical damage grows dramatically. The following is a partial list of engine components that can be harmed by engine knocking:

  • Heads of pistons: The piston head is the first component directly affected by engine knocking. The piston head may be perforated depending on the strength of the pinging.
  • Compression rings for pistons. Like the piston heads, the piston rings can resist increased pressures caused by engine knocking. A damaged compression ring isn’t as catastrophic as a blown piston head, but it still necessitates extensive engine work.
  • In some situations, the cylinder head itself may become perforated as a result of the increased pressure in the combustion chamber.
  • As you might expect, engine knocking can cause cylinder head valves to literally “melt.” Increased pressure causes an increase in temperature, which can rapidly exceed the material tolerance of the valves.
  • Higher pressure and temperature in the combustion chamber may cause increased wear of the valves, cylinder head, compression rings, and piston head, resulting in metal debris and fuel impurities entering the lubrication system and generating wear on other engines components.

11. Exhaust Smoke Is Black

Workout spark plugs can also act as a catalyst for thick, black exhaust smoke and increased carbon emissions. If you detect these bad spark plug symptoms, it’s time to see a mechanic or your local car service center because your problem is likely multi-layered.

12. The Check Engine Light Is On

It’s no surprise that your vehicle’s check engine light comes on when there’s a frequent misfire and inoperable combustion circumstances. Because a check engine light might indicate various issues, it’s advisable to have the vehicle scanned for trouble codes by a qualified repairer.

If your spark plugs have failed, your OBD scanner should display codes P0300 or P0171, which indicate a lean-running engine with misfires. A visual inspection is an effective approach to examining spark plugs at home. If you have a multimeter, though, you will be able to pinpoint the problem much more quickly.

13. Tailpipe Has A Strong Gas Smell

Another bad spark plug symptom is a gas smell from the exhaust fumes (for some insight, check out our guide on how to get gas smell off hands). Unburned fuel is leaking from the combustion chamber, causing this symptom. Fuel particles in the exhaust system can ignite (backfire), but they can also escape via the tailpipe. This is where the strong gas odor originates from; however, damaged spark plugs are simply one of several potential causes for this symptom.

Signs Of Bad Spark Plug Symptoms

If you’re not familiar with a vehicle’s engine, open the hood and check inside for a row of broad cables running down one side of the engine. The plugs are situated at the ends of the spark plug wires. The criteria below will help you determine how poor a spark plug is and when it should be replaced.

  • Keep an eye out for carbon deposits or fuel deposits on the plug. If you see any of them, it means the plug has to be replaced right away.
  • Take note of the fuel gauge on the vehicle.
  • If the car is practically consuming fuel, it’s a red flag that the spark plug needs to be checked first.
  • A light brown or grayish hue on the end of the spark plug indicates that the vehicle is not operating at normal temperature. The temperature of the car may rise as a result of malfunctioning spark plugs, causing significant damage.
  • When the engine has been utilized for a while, the brim of the electrode may resemble a sharp point. If that’s the case, it’s a sign that the spark plug has been used to its maximum capacity and has to be replaced right away.

Bad Spark Plug Symptoms

How To Diagnose Bad Spark Plug Symptoms

Even though the spark plugs appear to be in good condition, it’s possible that the spark plug wires have been damaged. Bad spark plug symptoms include engine stalling, low power, ignition issues, and uneven or harsh idling. As a result, the next time you open the hood, double-check the cables. It may be difficult to spot the fault because the wires are coated in thick insulators.

As a result, keep an eye out for a rip or tear in the insulating layer. Pay attention to the situation if there is an exposure to the insulating material. Start the engine at night and look under the bonnet for any sparks on the wire circumference. It’ll tell you if the cables need to be repaired or not.

Spark Plugs: How Long Do They Last Before Bad Spark Plug Symptoms Appear?

The status of your spark plugs can impact the engine’s performance. Despite their extensive use, Spark plugs don’t need to be replaced very often. The majority of manufacturers recommend replacing spark plugs every 30,000 miles; however, depending on the type of spark plugs in your automobile, you may be able to go up to 100,000 miles.

A copper spark plug, for example, will not last as long as a spark plug composed of a stronger substance, such as platinum or iridium. Whatever the case may be, you should always change spark plugs in pairs (one for each engine cylinder) and stick to the manufacturer’s recommendations for plug types (found in the owner’s manual).

How Much Does It Cost To Replace Bad Spark Plugs?

The price is totally dependent on the make and model of your vehicle. Some cylinders are more significant than others. Counting the cylinders is one method of determining the number of spark plugs in your vehicle. However, some automobiles use a dual-spark ignition mechanism. A V4 engine, for example, has four cylinders. There are two spark plugs in each cylinder.

Spark plug replacement is relatively inexpensive (make sure you also take into account how many spark plugs in a V8 and how to change spark plugs), regardless of the number of cylinders in your engine. A single spark plug is less than ten bucks. The cost of replacing all of the plugs, plus the mechanic’s time, should be between $40 and $150. It is not a difficult procedure, so the mechanic should be able to complete it in an hour or less.

When Should You Replace Them After Bad Spark Plug Symptoms?

Today’s spark plugs can last a very long time. They’re really tough, and they usually don’t go bad before their service interval, and they don’t have any internal combustion issues. Depending on the type of spark plugs recommended by your manufacturer, you should change your spark plugs every 10000-15000 miles.

Iridium and platinum spark plugs typically have a service frequency of roughly 10000 miles, however, if you use standard spark plugs, the service interval could be as early as 30000 miles.

Bad Spark Plug Symptoms

Rather than replacing just the faulty ones, you should replace all of your spark plugs at once.

You may observe heavy wear on one or a few spark plugs while the others appear to be in good condition, but you should always replace them simultaneously. Any workshop or mechanic will advise replacing the full set, but if you’re doing it yourself, remember that replacing one at a time isn’t worth the effort.

Evaluation Of Bad Spark Plug Symptoms

A defective spark plug can reveal a lot about the health of the engine and its components. Professionals frequently use it to assess the current state of an engine. We’ve gone through a few different spark plug conditions and what they mean in terms of engine health.

  • Electrodes that have become worn out are quite prevalent. It does not indicate a problem with the engine.
  • A dark and dry spark plug indicates a leaking fuel injector or a fuel control issue.
  • A spark plug that is absolutely clean and immaculate indicates coolant leakage in the cylinders. This coolant cleans the spark plug by steaming it and making it immaculate.
  • Normal engine condition is worn-out electrodes with no deposit or debris.
  • It’s not a good indicator if the end of the spark plug is dry and sandy. It shows oil seeping from the engine, which has reached the valve seals and other components.
  • Greasy-looking spark plugs indicate liquid oil penetration in the engine, indicating a leaking cylinder head or other severe issues.

What To Do If You Notice Bad Spark Plug Symptoms

The model of your car determines the technique. Some models are simple to replace, while others require more expertise. The spark plugs on some V-engine versions are difficult to access. It’s possible that you’ll end up accessing various engine components. However, all car models will follow the same procedure for replacing the spark plug.

It consists of:

  • To remove all of the ignition cables as well as the coins.
  • Remove any items that are covering the ignition coils/cables.
  • Replace all broken spark plugs with high-quality replacements.
  • Check the lengths of your sparks to ensure that you have the correct ones. Pistons can be damaged by spark plugs that are too long.
  • Lubricate the threads and tighten them using a torque wrench.
  • All removed items, including the ignition cables and coils, should be returned.

Final Verdict On Bad Spark Plug Symptoms:

A shell, an insulator, and a central conductor make up a spark plug. It’s a gadget that uses an electric spark to ignite a mixture of air and fuel. A spark plug is a component that is commonly seen in vehicle engines. Its primary function is to start the engine.

Spark plugs help start the car by providing a spark in the engine cylinders. It contributes to the vehicle’s continuous movement, efficient combustion, greater fuel efficiency and performance, and low gas emissions. Inadequate cleaning of the spark plug may result in its failure in a short period of time.

Keeping spark plugs in good condition and achieving effective performance is to change them on time and with caution. If your automobile doesn’t seem to be operating right, inspect each bad spark plug symptom individually and replace them all at once.

Spark Plug Problems: Need-to-Know Facts

  • Clean and undamaged spark plugs are crucial for optimum engine performance.
  • Dirty or fouled spark plugs can negatively affect how your engine runs.
  • Fouled or bad spark plugs can be caused by substances like oil, fuel, carbon, or from running too hot.
  • Symptoms of bad spark plugs include reduced gas mileage, lack of acceleration, hard starts, engine misfires, and rough idling.
  • Reduced gas mileage is a common symptom of bad spark plugs.
  • Lack of acceleration and sluggish performance can be attributed to bad spark plugs.
  • Difficulty starting your vehicle could be a result of bad spark plugs.
  • Faulty spark plugs can cause engine misfires or hesitations instead of running smoothly.
  • Rough idling and vibrations can also be caused by bad spark plugs.
  • Continuing to drive with fouled or dirty spark plugs can lead to more serious and costly problems.

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1 comment

Tracy 05/12/2022 - 12:27 PM

There are many ways through which spark plug amazingly works with the engine. I was particularly impressed by your article here.


hesitation caused by poor timing between the cam and crankshafts should be a red alert. Spark plug is soooo important. Thanks for the info.


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