How to Fix Misfire After Changin Spark Plug

Changed Spark Plugs and Coils But Still Misfiring? Here’s What to Do!

We know how annoying it is to replace something on your pride and joy only for it to do absolutely nothing, like in the case of misfires that still don’t disappear after dropping in a new set of coils and plugs from Thor himself.

But before you pass off your car as a lemon, you would definitely want to dig deeper into all the parts that create that controlled chaos inside your engine known as a “spark”.

So if your new spark plugs and coils still aren’t cutting it, then here’s what to do to rid your car of that pesky misfiring issue once and for all!

Why is my car still misfiring after changing spark plugs and coil packs?

If your car is still misfiring even after changing the spark plugs and coil packs, they may have been improperly installed, which affects their performance.

However, the misfiring can also be caused by other components like a faulty fuel injector.

Spark plugs and coil packs are both crucial in the proper combustion of fuel in an engine, though they can eventually go bad or wear out after thousands of miles of driving and cause your engine to misfire.

But what happens if you’ve replaced your spark plugs and coil packs yet the misfires don’t disappear? Well, there are still other potential reasons for this that are worth investigating.

For starters, if you’ve replaced your spark plugs and coil packs for the first time, then you can consider double-checking them to see if you’ve tightened and connected every single one of them properly.

Why is car still misfiring after changing spark plugs and coil packs

Any loose or disconnected component of the ignition system can disrupt the required flow of electrical current and voltage, which can affect the way that fuel is ignited inside the engine.

In other cases, the misfire may not even have anything to do with the spark plugs or coil packs, but rather problems with other components of the engine.

One such component is the fuel injector, which works hand-in-hand with the ignition system by providing the fuel that would be ignited by the spark plug.

If the fuel injector becomes faulty or gets clogged, it will not be able to provide adequate fuel to maintain the correct air-to-fuel ratio inside the engine, causing it to misfire and run rougher than usual.

What to Do If There’s a Misfire after Changing Spark Plugs and Coils

In the event the spark plugs or coils you used are defective, you need to get them replaced again since they can be a source of the misfire.

A misfire can also be caused by other faulty components, so it’s also important to check the spark plug wires, fuel injectors, and mass airflow (MAF) sensor.

If you are certain that your engine only started misfiring after changing your spark plugs and coils, and you’ve already confirmed that they were correctly installed, then you may have gotten a defective batch from the factory.

Just like any other product, there is still a chance that you have bought a faulty or even “fake” spark plug or coil, which will not be able to perform up to the standards that a proper one will.

In the case of spark plugs, there are certain ways to tell if they are the real deal or not by looking at the physical differences in the packaging and manufacturing quality, as shown in the comparison video below for NGK spark plugs.

Thus, it’s important to not only go for the recommended spark plug for your vehicle but to also be careful of buying any fake copies of such by only shopping at trusted stores.

On the other hand, if there is nothing wrong with the spark plugs or coils, then you need to start looking for other components that may have become faulty and are causing the misfire as well.

Misfires have been known to be caused by issues with your spark plug wires, fuel injectors, and mass airflow (MAF) sensors.

What do these components all have in common? Well, they’re all electronically operated and can start to malfunction after a certain period of time.

The fuel injectors, in particular, can become faulty when too much debris has built up, which can partially or completely clog them, resulting in a leaner fuel mixture and misfiring especially at idle.

Hence, it’s important to regularly check your engine bay and do some cleaning to preserve the life of your components. Be sure to replace any faulty components that you notice immediately.

How do spark plugs work?

Spark plugs provide the spark needed to ignite the fuel inside the engine’s cylinders to produce power, though they do so with very specific timing.

Spark plugs must ignite or fire according to the ignition timing of an engine to achieve optimum power and fuel economy with the least vibrations.

Spark Plugs Diagram

In any gasoline-powered combustion engine, the spark plug is the one responsible for creating the actual “spark” that’s needed to ignite the mixture of air and fuel inside the engine.

In today’s engines, each cylinder is assigned its own spark plug, which contains both a central electrode and a side/ground electrode at the bottom part where the spark actually comes from.

The more pointed top section of the spark plug is the terminal, which receives voltage from the battery either through a high-tension wire or an ignition coil.

The middle shaft or “insulator” of the spark plug is where voltage from the terminal flows through and into the central electrode via an internal wire. 

The insulator is then wrapped around by a metal housing or “shell” which the ground electrode is attached to at the end. So essentially, the insulator “insulates” the internal wire and central electrode from the shell.

Since the spark plug needs to operate with a high-voltage current made by the ignition system to create a spark, the voltage can measure between 5,000 volts and 40,000 volts, though this can be even higher depending on the type of spark plug.  

What are the causes of spark plug misfires?

What are the causes of spark plug misfires

Common causes of a misfiring spark plug include the spark plug being worn out, being improperly installed, oil or deposits building up and fouling it, and a faulty or damaged spark plug wire.

Worn-Out Spark Plugs

There can be several causes as to why your spark plugs can start to misfire, but one of the most common reasons is that they are simply past their lifespan and are already worn out.

The average lifespan of a spark plug can highly depend on what the spark plug is made of. But among the different types, iridium spark plugs generally last the longest.

Improper Installation

However, things such as spark plug type and lifespan all go out the window in the event that they have been incorrectly installed, which is another reason for them to misfire.

When your spark plugs are under-torqued or a bit too loose, they will not be able to fire properly, and apart from misfiring, it can also cause that cylinder to lose compression and make your engine run poorly.

Improper installation can also happen to the wires for the spark plugs. If you accidentally mix up the spark plug wires, it can cause the spark plugs to fire in the wrong order, leaving you with an even worse case of engine misfire.

This is why you should also take note of the original order of your spark plug wires, and one thing that helps a lot with this is by familiarizing the firing order of your engine.

Of course, having faulty or damaged spark plug wires will also do you no good, as this will obviously affect the flow of electrical current to the spark plugs and cause your engine to underperform.

Dirty or Fouled Spark Plug

Dirty or Fouled Spark Plug

In a running engine, spark plugs are constantly exposed to fuel, oil, and any other debris that’s a byproduct of the combustion process.

If the electrodes at the tip of the spark plug have too much debris buildup on them, it can start to affect their ability to create a spark properly.

While you can still clean and reuse a fouled spark plug, there’s still a high chance that it will not perform as well as it was before anymore.

Fouled spark plugs are usually caused by having too rich of an air-fuel ratio, a dirty air filter, a bad fuel injector, internal oil leaks, and idling your car for extended periods of time. 

What happens when a spark plug fails?

What happens when a spark plug fails

A failed spark plug can commonly cause a misfire to occur, resulting in the engine running rougher and having poorer performance.

The misfire caused by the failed spark plug can also potentially damage other parts like the ignition coils and even cause the engine to seize.

Spark plugs are tasked to provide the spark to ignite the fuel at a specific time and order. If even one of them fails, it will affect the entire combustion process and the performance of your engine will be hampered.

You may even struggle to get the engine to start or crank with a failed spark plug, as the amount of spark may not be enough to ignite the fuel and start the combustion cycle inside the cylinders.

If you still manage to start the engine even with a failed spark plug, it’s still a bad idea to leave it on for too long due to the misfire potentially causing damage to the engine and the catalytic converter.

Why is my engine misfiring with new spark plugs?

If your engine is misfiring after installing new spark plugs, then there may be a chance that they have been improperly installed or are defective.

However, issues with other components can also cause a misfire with new spark plugs, such as the ignition coils, spark plug wires, and fuel injectors. 

Can new spark plugs cause misfires?

New spark plugs can still potentially cause your engine to misfire if they have been installed incorrectly or are defective out of the box.

Be sure to double-check your new spark plugs as well as each of their wires to see if they have been tightened and connected properly.

Will replacing spark plugs stop a misfire?

Replacing worn-out or bad spark plugs can stop your engine from misfiring and bring back proper ignition timing for optimum performance.

However, you first need to confirm that the spark plugs are the ones causing the misfire. Otherwise, it’s best to check issues with other related components too.

What spark plugs should I use for my car?

What spark plugs should you use for car

It’s always best to use the recommended factory spark plugs for your car in the owner’s manual to get the best possible spark performance.

For instance, if your car originally came with iridium spark plugs, then it’s recommended to replace them with iridium ones as well instead of copper or platinum.

Using the table below, you’ll be able to compare the average lifespan of each general type of spark plug.

Aside from the material that the spark plug is constructed from, its average lifespan also depends on the exact brand and model of the spark plug as well as the engine that you’re going to use it in. 

Spark Plug TypeAverage Lifespan
Copper/Nickel10,000 to 20,000 miles (16,100 to 32,000 km)
Silver20,000 to 30,000 miles (32,000 to 48,000 km)
Platinum60,000 to 100,000 miles (96,500 to 161,000 km)
Iridium60,000 to 150,000 miles(96,500 to 241,000 km)

How to Prevent Spark Plug Misfire

How to Prevent Spark Plug Misfire

To prevent spark plug misfires, use good-quality spark plugs that are recommended by the manufacturer. Perform regular maintenance on your car to avoid debris buildup in the ignition system.

Follow the recommended intervals for changing your spark plugs, which can depend on the type your car has.

There can be many different things that can cause a spark plug to fire, which means that you should also make it a habit to check underneath the hood to see the condition of your engine bay.

While using the recommended spark plugs for your car is already a big plus to making sure they last longer, a dirty engine bay can still affect the performance of your ignition system.

If too much carbon debris has built up around your ignition system, then it can start to malfunction and cause a misfiring spark plug.

Be sure to check for any sources of oil leaks that may be causing debris buildup on the ignition system and get it remedied right away. If there is an internal leak coming from the engine itself, then you may have worn-out gaskets that need replacing.

It’s also important to familiarize yourself with the recommended replacement interval for the type of spark plugs you have, as not every spark plug has the same average lifespan (check the table above for reference).

What to Do If Only One Cylinder Misfires

What to Do If Only One Cylinder Misfires

A single cylinder misfiring commonly means that there is something wrong with the spark plug of that specific cylinder.

Apart from that, you should also check the misfiring cylinder’s ignition coil and fuel injector for problems. That cylinder may even have low compression compared to the others.

Even if your vehicle’s ECU (or computer) only detects one cylinder misfiring, you need to get it looked into right away before it ends up causing even more damage to the rest of the engine.

A bad or fouled spark plug is a very common cause of one cylinder misfiring, but it can also be caused by low compression in the cylinder or a bad ignition coil.

The misfiring of one cylinder can also be due to it not receiving enough fuel, which can commonly be traced to a clogged fuel injector for that specific cylinder.

All the culprits mentioned above all have one thing in common, which is that they can affect the delicate balance between air and fuel inside the cylinder, which will make it difficult for the spark plug to properly create a spark at the right time.

Thus, make sure to get your vehicle diagnosed by a professional mechanic right away if you feel anything unusual about how your engine is running, as you may have a misfiring cylinder. 

What does an ignition coil do?

What does an ignition coil do

An ignition coil is a component that transforms low-voltage signals from the battery to high-voltage signals needed in the engine combustion process.

Ignition coils use two copper coils wrapped around a core. Thousands of volts pass through this system and into the spark plug to ignite the fuel. 

When it comes to a modern car’s ignition system, we shouldn’t forget to talk about a very important component that converts electrical current from the battery to one that’s actually usable for creating a spark, the ignition coil.

Older cars from several decades ago used to only have one ignition coil that works with a distributor to transform voltage, while today’s modern engines have now moved on to a distributor-less system that has one coil for each spark plug.

Just about every gasoline-powered engine has an ignition coil as the source for high-voltage signals. If one coil was to become faulty, then the spark plug that it’s connected to will not receive enough voltage to create a spark.

Symptoms of a Bad Ignition Coil

Symptoms of a bad ignition coil include engine misfires, an illuminated check engine light (CEL), poorer performance and fuel economy, rough idling, and a jerky engine.

A bad ignition coil can also cause increased engine vibrations, difficulty starting, and backfire through the intake or exhaust. 

How to Test an Ignition Coil

To test if an ignition coil is still working, you can connect it to an ohmmeter or multimeter to see if there is any resistance in the circuit.

You can also test if the coil still works by looking for a spark in the spark plug wires, which will tell you whether or not it’s still sending volts.

If you suspect that one of your ignition coils may not be working, then there are two common ways to test or troubleshoot them.

The first way is to use an ohmmeter or multimeter and measure the resistance of each ignition coil.

To do this, you first need to remove the end of the ignition coil and set your device to display “ohms” for resistance, then connect the two test probes of the device to the first and last terminals of each ignition coil.

All of your ignition coils should have the same reading on your ohmmeter or multimeter. If one of them has a lower reading than the others, then you have located the faulty coil.

If you don’t have access to an ohmmeter or multimeter, the second way is to check if there is a spark in each spark plug wire. 

No spark present would mean that the spark plug wire is not receiving electrical current from the ignition coil, making that specific coil the faulty one. 

Why does my car misfire after I changed the spark plugs and coils?

If your car misfires after changing spark plugs and coils, then they may have been installed incorrectly, are defective out of the box, or there is an issue with other ignition system or fuel system parts.

Engine misfires can also be caused by a cylinder with low compression or an electrical problem.

Frequently Asked Questions (FAQs)