Symptoms of Bad Spark Plugs – and When to Replace

Driving your car continuously with spark plugs that are going bad can cause engine damage. It’s easier to change spark plugs than to repair a damaged engine. What are the symptoms of bad spark plugs, and when to replace them?

There are many symptoms of malfunctioning or damaged spark plugs. You need to replace them when you see these signs:

  1. Hard to start the engine
  2. Check Engine light is on
  3. Slow to accelerate
  4. Poor fuel economy
  5. Engine misfires
  6. Rough Idling of the engine
  7. Engine noise is very loud
  8. Engine hesitates while accelerating
  9. Time to change spark plugs according to manufacturer

The most common cause of spark plugs going bad is overheating the tip of the spark plug. If this condition is present while you are driving your car, the spark plugs will frail prematurely. Additionally, a malfunctioning cooling system or pre-ignition heat buildup inside the combustion chamber can cause spark plugs to go bad.

Read on to learn more about the symptoms of spark plugs going bad, some relevant details about them, and when you need to replace them.

Also, for an excellent spark plug, take a look at NGK 5464 BKR5EIX-11 Iridium Spark Plug on Amazon for its price and great reviews:

Click here to see it on Amazon.

Symptoms of Bad Spark Plugs

Symptoms of Bad Spark Plugs

You will know when the spark plugs in your car engine are going bad if you know all the bad spark plug symptoms. If you see these signs, these spark plugs are up for a replacement:

  1. Hard to start the engine
  2. Check Engine light is on
  3. Slow to accelerate
  4. Poor fuel economy
  5. Engine misfires
  6. Rough Idling of the engine
  7. Engine noise is very loud
  8. Engine hesitates while accelerating
  9. Time to change spark plugs according to manufacturer

Reasons Why Spark Plugs Malfunction

Why do spark plugs go bad? There are two primary reasons why spark plugs malfunction:

  • Malfunctioning Car’s Cooling System
  • Heat buildup in the engine’s combustion chamber due to a pre-ignition condition that occurs while starting the car.

So that you’ll not be surprised when the Check Engine light suddenly comes on, the rest of this article dwells on the details of the symptoms of failing spark plugs.

More on Symptoms of a Bad Spark Plug

what causes bad spark plugs

1. Hard to Start Car

We often blame a discharged battery if the car doesn’t start after cranking the engine several times. We often ignore the fact that spark plugs can also be the cause of hard starting problems.

Spark Plugs Provide the Initial Spark to Ignite the Fuel and Air Mixture

The spark plugs are the ones that provide the initial spark that ignites the fuel and air mixture inside the engine chambers to make the engine turn and run. If these spark plugs are already worn out or clogged with soot, the engine has to work harder to compensate for it to start running.

If your car won’t start at all, a discharged battery is the culprit. However, if the engine cranks but won’t start, the battery is not the problem. Perhaps it is one of the spark plugs or all of them.

2. Check Engine Light Suddenly Comes On

Spark plugs that are going bad or damaged can trigger the Check Engine light on your dashboard. Modern cars are fined tuned so much that any issue that will compromise the efficient functioning of the engine will cause the Check Engine light to turn on.

Damaged Spark Plug Can Cause Misfire

One of these issues is a bad spark plug. If even one spark plug fails to deliver the needed spark, it will cause a misfire in its particular combustion chamber. As a result, the Check Engine light will instantly turn on.

Many things can trigger the Check Engine light, not just misfiring or bad spark plugs. But since one of the triggers is a bad spark plug, you must include them in your regular preventive maintenance.

3. Engine Struggles While Stepping on the Gas

There are two reasons why your car struggles while you are accelerating:

Problems With the Ignition System

Several sensors in your car’s ignition system send signals to the car’s onboard computer about the right time to send electric pulses so that the spark plugs will fire. If there’s a faulty sensor, there will be misfiring of the spark plugs.

Worn Out or Bad Spark Plugs

If this is the condition of the spark plugs, they may not generate the spark required to ignite the fuel and air mixture of the engine. In short, they will not be effective and will considerably affect your car’s capability to accelerate. Your car will lack the energy to go fast quickly.

4. Your Car Is No Longer Fuel Efficient

If you find yourself gassing up more often than before, your car is experiencing poor fuel economy. In other words, it is no longer efficient in burning the fuel inside the engine. This is one of the bad spark plug symptoms that you need to be aware of.

Old and worn-out spark plugs are not good at igniting the fuel and air mixture inside the combustion chamber. A lot of this mixture will go unburned. The black cloud of smoke in your tailpipe every time you step on the gas is one proof of this condition.

According to the National Institute for Automotive Service Excellence, a spark plug that misfires can reduce your car’s fuel efficiency by 30%. That’s how crucial good spark plugs are in the efficient operation of a car engine.

5. Engine Misfire

When a car engine misfires, the most obvious cause is a faulty ignition system. In most modern engines, some of the causes include a malfunctioning sensor, a defective spark plug wire, or a damaged spark plug’s tip.

Other reasons for a misfire include poor fuel quality and a bad ignition coil plug cap. When an engine misfires, it will send unburned fuel directly into the exhaust. This will ultimately destroy the catalytic converter.

6. Rough Idling of the Engine

Bad spark plugs can cause rough idling of a car engine. You will notice it if you hear a rough sound when your car is in neutral gear. When the engine is fully efficient, it will purr just like a kitten when it’s neutral.

However, when there’s something wrong in one or two of its components, it will produce strange noises like rattling, pinging, or knocking. You will also feel that its vibrations are more than normal. The culprit may be one or all of the spark plugs. This can cause misfiring in the cylinder while the engine is idle.

7. Overly Loud Engine

When a spark plug in one cylinder of the engine malfunctions, you will not be able to ignore the sound it generates. This is true whether your car engine has four, six, or eight cylinders.

If the efficiency of just one of the cylinders is reduced, the other cylinders have to compensate. This situation overworks all the cylinders. It will manifest as strange noises like knocking and rattling.

8. Engine Hesitates While Accelerating

When you notice that the engine hesitates when you step on the gas, the spark plugs may be a problem. The engine is not responding to your stepping on the gas. Its power may surge at the start, but then it slows down right after.

The engine could be sucking in more air than should be introduced in the combustion chamber, which delays power delivery. If there seems to be a combination of hesitation and surging of the engine, it is probably a problem with the spark plugs.

When to Replace Spark Plugs

symptoms of bad spark plugs in car

Manufacturer Suggests Maintenance Schedule

It’s time to change the spark plugs of the engine if the car manufacturer says so. Your car came with a suggested maintenance schedule provided by its maker. It is best to follow their advice regarding the time to change the spark plugs. Whether you are experiencing spark plug problems or not, you need to follow these recommendations.

Most Spark Plugs Have Long Lives

Most spark plugs have long service lives. They don’t wear out that fast. Some people say that a spark plug should last around 80,000 miles before it is replaced. However, check your car’s spark plugs by having an engine tune-up if you notice any symptoms above.

Some Say Spark Plugs Can Last from 20,000 to 30,000 Miles

On a more reserved note, others say that spark plugs can last from 20,000 to 30,000 miles. According to the U.S. Federal Highway Administration, the average mileage of spark plugs is about 13,476 miles. If you translate that to years, a spark plug should last from 1.5 to 2.25 years.

Best Replacements for Bad Spark Plugs

You need to ask the next question: where can I get the best spark plugs that last long? Amazon.com is the best place where you can buy the most long-lasting spark plugs in the market. Here are some of the spark plugs they sell:

1. NGK 5464 BKR5EIX-11 Iridium Spark Plug

One of the spark plugs that are durable and tough is the NGK 5464 BKR5EIX-11 Iridium Spark Plug:

Click here to see it on Amazon.

This is a pack that consists of four spark plugs. The tip of this spark plug is made from a special material called Iridium IX.

These spark plugs offer superior ignitability, excellent anti-fouling, and improved throttle response and are designed specifically for car owners concerned about engine performance.

2. NGK (7092) BKR6EGP G- Power Spark Plug

Another spark plug that you can consider is the NGK (7092) BKR6EGP G- Power Spark Plug:

Click here to see it on Amazon.

The pack comes with six pieces of spark plugs. These spark plugs have platinum electrode tips. Their manufacturer claims that they can last from 30,000 miles to 40,000 miles.

3. NGK # 1465 Laser Iridium Spark Plug IZTR5B11

The NGK # 1465 Laser Iridium Spark Plug IZTR5B11 is another excellent spark plug that you can consider:

Click here to see it on Amazon.

One pack consists of eight spark plugs. Car owners who replaced their old spark plugs with these new ones have experienced increased gas mileage and improved engine performance.

Conclusion: Symptoms of Bad Spark Plugs

The car engine will show you several signs when its spark plugs are going bad. When you experience these symptoms, it’s time for you to replace them.

  1. Hard to start the engine
  2. Check Engine light is on
  3. Slow to accelerate
  4. Poor fuel economy
  5. Engine misfires
  6. Rough Idling of the engine
  7. Engine noise is very loud
  8. Engine hesitates while accelerating
  9. Time to change spark plugs according to manufacturer

Related reading:

Battery Light on but Alternator Is Charging – Cause and Fix

Ford Triton Spark Plug Repair Kit [5 Best Kits]

Iridium Vs Platinum Spark Plugs – What Are the Differences?