Spark plugs are incredibly easy to replace on most vehicles. They are also fairly inexpensive in comparison to most other components on your car. Worn spark plugs do have clear symptoms, they often blend or correspond with ones caused by other problems. In other words, it could be tricky to diagnose them properly!

Fortunately, there are steps you can take to make sure the vehicle does indeed have worn spark plugs. Keep in mind, spark plugs also have service intervals that have to be followed whether they are worn or not. This troubleshooting guide will prove useful to those facing premature failure or to those who aren’t well-versed in the service history of the vehicle in question

Importance of Spark Plugs

Spark plugs have an important role when it comes to a combustion engine and many components rely on them to perform optimally.

As their name suggests, spark plugs are essentially insulated plugs that screw into the cylinder head to provide the spark. It’s this spark that the engine uses to ignite the mix of air and fuel in the combustion chamber. Spark plugs also function to take the heat away from the combustion chamber by pulling thermal energy away from it. 

Here’s a slightly more detailed explanation of what goes down: The spark plugs are positioned at the top of the cylinder head. The pistons which sit below it in the block move up and down in the cylinder. When the piston moves downwards it allows for a mix of air and fuel to be collected in the space between the plugs and the top of the piston.

When the piston makes its way back up again it compresses the air and fuel. It is at this point that the spark plug comes in as it ignites the mixture when the piston reaches the top dead center. This causes an explosion inside the cylinder and the pressure that is generated from it sends the piston back down. The resulting movement of the piston is what generates power for the car in question.

This process is continuously repeated at different rates of speed depending on the input of the throttle. Most engines have one spark plug per cylinder, while some have two. This means a 3-cylinder engine has 3 spark plugs and an 8-cylinder engine will usually have 8 spark plugs. 

If you suspect that your spark plugs are worn, or you just want to follow your car manufacturer’s recommended service intervals for this component, you’re in the right place! We offer a wide range of quality spark plugs from brands such as NGK, Denso, Bosch and others! Check our catalog for the complete offering. 

Signs of Worn Spark Plugs

The following list consists of the most common symptoms and signs of worn spark plugs. However, as mentioned earlier, these symptoms could be caused by another issue. That’s why it’s recommended to inspect the potentially worn spark plugs before pulling out the parts cannon.

Misfires

Considering just how vital spark plugs are in the combustion process, it shouldn’t come as a surprise that worn ones can cause misfires. Yes, something as small as worn spark plugs can lead to one of the most concerning engine problems — misfires. Misfires will be noticeable as they won’t only produce an unusual sound, but also affect power delivery.

Power Delivery

Speaking of weak power delivery, it too is a sign of worn spark plugs. This usually occurs earlier than the others signs as it is among the first symptoms. Slightly worn spark plugs can affect the performance of the vehicle. This can occur without misfires which can make it hard to spot.

Acceleration Issues

While we are on the subject, worn spark plugs will lead to issues with acceleration. This is easy to spot as it can be quite noticeable, especially when overtaking on the highway. You will notice a reduction in the sensitivity of the accelerator altogether. 

Starting Woes

While we usually associate starting problems with a weak battery or low fuel, worn spark plugs could also be the cause. Spark plugs deliver the much-needed spark required to get the engine going. In such a situation, it’s still advisable to inspect the aforementioned issues before moving on to inspect the spark plugs.

Idle Trouble

Another sign of worn spark plugs is a rough idle. As the engine relies on good quality spark plug, any problems or wear can affect multiple functions including its ability to idle correctly. One can easily tell if their vehicle isn’t idling correctly if the RPM gauge is bouncing around.

Surging

There are times when worn spark plugs can lead to surging. While this is not as common as the other signs, there’s a possibility of its occurrence. Worn spark plugs can affect the combustion process wherein leads to excess air being sucked in. This can cause an engine with worn spark plugs to surge.

Low Gas Mileage

Another symptom of worn spark plugs that shouldn’t be ignored is a poor gas mileage. If you notice your car delivers less than normal gas mileage, worn spark plugs should not be ruled out. If it is indeed the issue, it can be resolved quickly by swapping in fresh OEM quality spark plugs.

How to Inspect Worn Spark Plugs?

While the signs of worn spark plugs mentioned above raise the possibility of it being the problem, it can only be confirmed with an inspection. The difficulty of this process depends on the vehicle in question as some spark plugs can be easier to replace than others. Interestingly, many technicians inspect spark plugs to determine the health of the engine. Once you have the spark plugs out, you can inspect them by looking for the following changes on the tip.

If the tip of the spark plugs looks unchanged, it’s a good sign. This indicates that the spark plugs and engine are in normal condition. A light gray shade also indicates the same thing. However, if there’s no major change but still shows signs of wear it’s time for replacements. It’s also important to stick to the service intervals when it comes to sparking plugs. When they reach the recommended miles, it’s time to swap in a new set regardless of the condition.

If the car continues to suffer from one of the symptoms mentioned above even after installing new spark plugs, it means the cause of the problem lies somewhere else. This is where an inspection of the older spark plugs can come in handy. There are several types of inconsistencies one can find on bad spark plugs, they include — detonation damage, fuel or carbon fouling, red tip, oil ash, and preignition. We will have a thorough guide on reading spark plugs posted at a later date, so don’t forget to check back!

Spark Plugs Are One of Our Top Sellers!

One of the most popular products in the Newparts.com shop are spark plugs. We believe the pricing and service we offer when it comes to high-quality spark plugs have to be amongst the best in the country! If you’re looking for a set of spark plugs, head to our Shop and check what we have to offer right now!