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Symptoms of Bad Spark Plugs

Symptoms of Bad Spark Plugs

Spark plugs play an important role in your engine performance, as well as its lifespan. Your spark plugs should be regularly inspected and changed, according to the specifications in your owner’s manual. If you are not the first owner, you should assume they need switching out and begin your own maintenance schedule. Whether your vehicle is new or new to you, don’t forget to have the right auto coverage before you set off down the road. 

Spark Plugs and Engine Performance 

Spark plugs are small compared to the giant job they have to do when it comes to your engine. Besides trouble starting the car, faulty spark plugs can play havoc on your engine performance and your fuel consumption. That’s why it is important to keep track of these small but important parts.  

How do Spark Plugs Work 

Internal combustion chamber engines start when a “spark” of electricity ignites a combustible air-fuel mixture. Your plugs take in high energy voltages and cause the spark needed to cause the combustion process. Barely bigger than your finger, they have a critical role in your engine’s continued routine of starting when you turn the key (or press a button), as well as your fuel efficiency and emission levels. When they begin misfiring, they can cause issues. 

Bad Spark Plug Symptoms 

These hard workers are on duty anytime you need to start your vehicle and they don’t quit after that. They play an important role in the continued good operation of your car or truck. That’s why it’s important to replace them when they begin to wear out. Here are some symptoms that your “sparky” needs “sparking.” 

Misfiring Engine and Noises 

Any unusual type of engine noise is a reason to take a closer look. If you play the tunes loudly, you must occasionally turn it down and listen carefully to anything your car may be trying to tell you. Noises that mean something is wrong include pings, rattling and knocking. These noises can be caused by engine misfires. 

Poor Acceleration and Power Loss 

When you press on the accelerator, does your car hesitate before gaining speed? The poor response to your direction to go faster can be a sign of spark plugs that need updating.  

Rough Idling 

When you are sitting at a stop light and your vehicle is making too much noise or acting like it wants to quit and go home, you may have a spark plug issue. You may also have some other issues, but checking the plugs is easy to do, so start there. 

Trouble Starting Car 

Your plugs have one main job: helping in the engine startup process. If you are running into trouble there, especially on colder days, the first place to check is the ignition and fuel system, including the plugs. 

Poor Fuel Consumption 

A sudden drop in gas mileage is a warning sign something is wrong. There are many different engine problems that may cause this, but if you are lucky, it is the spark plugs that simply need replacing: an easy and low-cost fix. 

What Causes Bad Spark Plugs 

Mostly spark plug issues result from normal wear and tear, although they may become distressed faster if some other related component is having an impact. Some driving behaviors can also have an effect on your plugs’ performance and longevity, including driving too slow over time, using an incorrect fuel/air mixture or idling for long periods. 

Luckily, for the most part, bad spark plugs take time to become an issue, so they typically won’t be a reason your vehicle suddenly quits on you. 

Normal Wear and Tear 

As with all parts of a moving engine, the plugs will eventually wear out from normal wear and tear. Spark plugs don’t require lubrication like other moving parts, but using a poor or bad type of oil can affect them due to deposits. 

Carbon Deposits 

Carbon is a by-product of burning gasoline, so after time, all components of your engine systems will show deposits of carbon. This can affect the engine performance in valves, chambers, nozzles and pistons, which is why your vehicle should receive regular maintenance. 


If your engine is overheating, your plugs may become “blistered” from the heat. This is something you can check with a visual examination, but keep in mind that an overheating engine can cause damage to a variety of parts. 

Knowing When Your Spark Plugs are Bad 

If you notice that your engine is gradually becoming less responsive or is harder to start on a cold morning, it could be a sign of a poor spark. If your dashboard lights come on, it’s important to know what they mean. A check engine light is especially concerning. Spark plugs operating under optimal conditions typically last up to 80,000 miles, so keep a close eye especially after that mileage. 

Visual Inspection 

Only gasoline-powered engines get their spark from a plug that shoots out electricity. If you are experiencing performance issues and you are even slightly handy around vehicles, you can do a visual inspection (and even replace them, if necessary). They are usually on the top of the engine, bolted to the cylinder head. Some engines have them on the side. If you choose to do this yourself, look for these signs of a bad spark plug: 

  • Buildup of various fluids or debris: If your spark plug is misfiring because it is covered in dirt, you may be able to clean it off with an abrasive. 
  • Component problems: Whether it’s a worn electrode or a cracked insulator, these two plug components cannot be fixed when they go bad. Any signs of melting or cracking mean it is time to replace, not repair. 

If you are not comfortable delving into your car’s engine, take it to the dealership or your favorite repair shop for an engine tune-up for peak performance. If you do this on the recommended maintenance schedule, you’ll help your car live longer, as well as stop problems before they become expensive. 

Why You Shouldn’t Delay Repairing  

If you’ve got a faulty spark plug, you should repair or replace it as soon as possible. As with all interconnected parts of an engine, one little problem may cause irreparable or highly expensive repairs to another part. Driving your vehicle when it is exhibiting signs of trouble may lead to a larger headache (or public transportation) sooner rather than later. 

Cost of Spark Plug Replacement 

The average cost to replace a set of spark plugs is wildly variable and ranges from $30 to $150, depending on the type and quality. However, given that they play an important part in the life of your vehicle, it’s better to replace them or at least inspect them on a regular basis. 

Preventive Maintenance Tips 

Spark plugs should be inspected every 30,000 miles or every two to three years, whichever comes first. It can be done as part of your regular car maintenance

Using Quality Fuel and Oil 

Your choice of fuel and oil impacts not only “sparky” but every other component of your engine. Make sure you purchase your fuel from a respected fuel stop and always choose quality oil. 

Protect Your Vehicle’s Lifespan with Comprehensive Coverage from Freeway Insurance 

At Freeway Insurance, we want to help you understand how your car works so you can take the best care of it and have it last a long time. Likewise, we want you to have the best protection when you are behind the wheel. Reach out to our agents for a fast and free car insurance quote by calling us at (800) 777-5620, stop in one of our convenient locations or simple go online for a quote. 

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