10 Symptoms of Bad Spark Plug & Replacement Cost

The engine is one of the most important parts of the vehicle. It contains multiple parts and the spark plug is one of them. A spark plug plays a significant role in internal engine combustion and being a daily function of your vehicle. A spark plug may be small but it is an incredibly important piece of equipment and a daily function of your vehicle; it’s job is to start a car. The spark plug does this by creating a spark which in turn ignites the air-fuel mixture in the combustion engine.

The spark plugs send the engine’s piston into action and then they continue to  provide the power necessary to keep the vehicle in motion as it makes its way down the road. But because the spark plug is tiny and out of sight, it can be easy to miss out on giving it proper care and time. If a car owner forgets to take their in for a regular tuneup, the vehicle may start to exhibit signs that it needs attention.

   It is necessary for the vehicle owners to recognize the symptoms of bad spark plug.

Symptoms of Bad Spark Plug

Bad spark plugs, while seemingly complex, are fairly straight-forward and pretty simple to point out especially for the car’s expertise.

The efficient working of the spark plug is very important. When the spark plug goes bad, it produces different symptoms that need to be replaced.

Here are some of the common symptoms of worn-out plugs or spark plugs:

  • Loud noise of engine
  • Rough Idling
  • Trouble Starting the Engine
  • Poor Fuel Economy
  • Poor Acceleration
  • Misfiring of Engine
  • “Check Engine light “ turns on
  •  Engine Hesitation
  • Engine knocking 
  • Over Heating
  • Loud Noise of Engine

No matter, if you are driving a car with a four, six or eight cylinder engine, unpleasant noises coming from the engine should let you know that at least one of the spark plugs is acting up. These really loud noises indicate that the cylinders are being overworked which will lead to further damages down the lane.

The malfunction of spark plug reduces the effectiveness of the engine’s cylinder that will lead to the rattle of the cylinder.

  • Rough Idling

Ideally, your engine sounds smooth and steady but if the spark plug does not generate spark according to the requirements, it means that you are likely to experience a rough idling. Specifically, if a car owner feels excessive sound vibrations, hears rattle noises and sees abrupt surges & drops in the internal combustion engine’s RPM; they should not put off inspecting it. Also, these vibrations can be disconcerting which cause damage to sensitive components if left untreated.

These sounds are a definite sign for the car owner that it is time to. at the  very last, scheduled an appointment to have their spark plugs checked out by a professional.

Rough engine idling can happen when your Electric Control Unit (ECU) tries to compensate for a failing spark plug and loss of power.

  • Trouble Starting the Engine

If your vehicle struggles to start after attempting multiple times, it could be a sign that your spark plugs are worn. Continued hard starts can also damage your engine’s ignition system and drain the car battery. When you have a faulty or bad spark plug, it can’t produce the power needed to start the combustion process which may result in shaky start or crankiness of your vehicle for a long time.

To ignite the air-fuel mixture of all cylinders in time, the engine requires a powerful ignition spark. So, if  one or more plugs are not working efficiently then your vehicle engine will not get the spark according to the requirements which can further cause one or more cylinders to malfunction and make it difficult for the engine to start.

Being protective about spark plug maintenance can extend the life of your engine by hundreds of thousands of miles.

  • Poor Fuel Economy

According to the study conducted by the institute for Automatic Service Excellence, a faulty spark plug reduces the fuel economy up to 30 percent and a spark plug can still go bad even with the correct heat range. It can happen due to several factors such as Excessive fuel activities and advanced engine wear.

As the weak spark plug cannot fully ignite and utilizes the fuel mixture, worn out plugs contribute to bad gas mileage by causing wastage of fuel. If the spark plug is not working properly as it should, it consequently forces your engine to consume more fuel – hence, drop in gas mileage. A quick reduction in gas mileage is one of the clear symptoms of the bad spark plug which can negatively affect the fuel economy.

  • Poor Acceleration 

I cannot stress enough how vital a working spark plug is to a vehicle. The car’s failure to accelerate is a very obvious sign that the spark plugs need to be replaced. Interestingly enough, sluggish performance of the car can also be due to lowered fuel injection  or a dirty fuel pump.

Poor acceleration requires immediate attention as it could put you in danger when switching lanes or while driving.

 However, since a bad spark plug is the most common culprit for engine hesitation, start by troubleshooting your spark plugs.

  • Engine Misfire

Misfiring is the most common term for what happens when or all of the fuel in the chamber fails to ignite. An engine misfire usually indicates that you have got a fouled spark plug. Many things cause an engine to misfire like an inferior quality fuel or leaky valves but those offenders may not be the only causes behind this particular issue though. The fuel mixture; not properly igniting spark plugs can surely be one of the causes.

An engine misfire can be noticed by the intermittent stumbling or stumbering sounds from the engine . An engine misfire can often be the result of at least one timeworn spark plug by the engine.

A misfiring engine must work harder and consume more fuel in order to deliver the power you need resulting in decline in the fuel economy of the vehicle and performance. If the problem is left unattended, it can also lead to the damage of the catalytic converter and can result in costly repairs.

Some of the other reasons of misfiring engine are:

  1. The engine is not getting sufficient oxygen needed to burn the fuel.
  2. The engine is not getting the desired amount of fuel.

The “ Spark Misfire “ is another problem that occurs due to the damaged spark plug that disrupts the combustion process and causes an engine to misfire.  So, if your engine starts misfiring, do check your spark plugs immediately and replace them.

  • “ Check Engine Light “ Turns on

Vehicle’s secondary reaction to faulty spark plugs is an activated CEL. Why is it a secondary reaction? It is because a spark plug does not throw fault codes all the time.

The internal of  the has tools in place to alert you that a car maintenance appointment needs to be scheduled even if no odd noises are not  yet coming from the engine. Paying attention to the “check engine light” can be really helpful. This light usually comes on if your engine has running issues due to a bad spark plug, overheating or oil contamination. It may also activate if there are issues like low fuel, low engine oil and a faulty fuel pressure sensor etc.

When your vehicle illuminates the check engine light, you should inspect all the parts to find the main issue.

  • Engine Hesitation

Engine hesitation  is another common symptom associated with bad spark plug that you will notice while accelerating. In this case the engine is not responding correctly to the driver; it may suddenly surge in power then slow down which means that engine is sucking in more air than it should be in its combustion process.

An irregular ignition of the fuel mixture is quite obvious to create hesitations due to the sporadic combustion taking place.

In some cases , spark plugs are also found to have an effect on acceleration from the startup.

  • Engine Knocking

As the spark plug goes bad, you may hear a knocking sound from the engine. and this problem may cause complete failure of the engine if it is left unaddressed. Ever wondered about the knocking noise coming from your engine when you depress the accelerator?  A cause behind that unusual noise is that bad or faulty spark plugs cause oxygen sensors to malfunction as a proper emissions device and a car ends up with surplus fuel and vapor inside its combustion chamber, causing issues with engine operation.

Engine knocking can cause irreversible damage to your piston compression rings, cylindrical head valves, cylindrical head and other critical engine components may also be affected due to the damaged spark plugs.

  • Over Heating

Multiple things can trigger your engine to overheat but when it comes to spark plugs, one of the two things could happen. When the spark plug is loose, it will likely overheat and cause backfiring. As a result, you may notice that the car’s exhaust emissions smell like gasoline. The engine may emit black smoke due to engine oil entry in the combustion chamber. If the spark plug is too tight, it causes the internal components and insulators damage, resulting in operating problems.

As driving with bad spark plugs can cause numerous problems; it is better to take preventive measures before time rather than to suffer from the above symptoms!

Causes of Spark Plug Failure

To avoid any unforeseen and on road expenses, a driver must seek help from a trusted mechanic to avoid complications.

Thankfully, You are also able to tell what has caused your spark plug to become defective based on its appearance.

  • Spark Plug Gasket Insufficiently Crushed

          Cause : Incorrect tightening of the spark plug can cause damage.

Remedy :  Tighten spark plug according to the recommended torque values by OEM.

  • Grayish Tan to White Colour around Insulator

Cause : Normal spark plug wear or operation that occurs naturally when the plug reaches its service limit.

Remedy : Replace the spark plug with the recommendations of OEM.

  • Ground Electrodes

Cause : Poor fuel economy and general engine wear.

Remedy : Make sure that spark plug heat range is correct and check for engine wear.

  • Rounded Center

Cause : General wear and tear.

Remedy : Get the replacement spark plug of the same heat range.

How Long Does a Spark Plug Last?

Your spark plug life span can vary greatly depending on the type of spark plug (for instance; a copper spark plug or a silver spark plug). Collectively, spark plugs can last from 12,400 to 150,000 miles. However, manufacturers recommended changing the spark plug every 30,000 miles because beyond that limit spark plug will start to decay, wear or foul.

How Long Does a Spark Plug Last
  • Copper- It is the most affordable and best performing option in the market, their copper core is coated with nickel alloy. But they must change more often than the others; roughly every 12,400 miles.
  • Iridium- NGK spark plugs have a life expectancy of 40,000-50,000 miles or sometimes even higher. The NGK laser iridium spark plugs typically last between 80,000 to 100,000 miles; these are equivalent to approximately 3,000 to 4000 hours of engine uptime.
  • Platinum-  Although platinum spark plugs give a weaker spark but will outlast copper and some iridium spark plugs. The life expectancy of a double or a single platinum spark plug is within 40,000 to 50,000 miles which is ideal for the car owners who prefer longevity.
  • Silver- Silver spark plug is used in European cars and special performance motorcycles. Although it is slightly ahead of the copper plugs at approximately 20,000 miles, the silver spark plug does not last longer than copper or iridium due to its durable metal composition.

If your vehicle has frequent maintenance intervals then a copper spark plug would be the best one for you. Otherwise, any of the other  options would do you well.

Is it Okay to Drive with a Faulty Spark Plug?

Continuing to drive on worn-out or damaged spark plugs may not be immediately dangerous for your life but can ultimately cause engine damage. Malfunctioning spark plugs cause engine problems which include lack of acceleration, reduced gas mileage and misfires. Driving with a faulty spark plug will be difficult because the engine might fail to function so don’t put it off.

Continuing to drive your car with a bad spark plug is like pushing your luck and asking for repair expenses to double so as your anxiety.

Replacement Cost of Spark Plug

The replacement cost can vary depending on the make of the model, type, condition of the engine, labor fee and the  choice of spark plug. Prices will also vary depending on your vehicle, how far gone bad the issue of spark plug is.

Collectively, replacing a spark plug can cost you around $100-$250 on low end and about $250-$500 on high end.

Final Thoughts

Every car owner wants their vehicle to perform at an optimal level and in order to achieve this goal – proper maintenance must be applied. If you notice any of the common signs of bad spark plugs mentioned above, get your spark plugs replaced ASAP before they create more complications. Also, don’t do it yourself if you are inexperienced.

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