Understanding Engine Misfires: Causes, Symptoms, and How to Fix Them

Reading Time: 4 minutes

We all have seen a car with black smoke coming out from its exhaust. If you have driven older cars, you might know the feeling of the engine suddenly “coughing” and causing the car to sputter and slow down.

These situations are often caused by a misfire cylinder. Most drivers have dealt with a misfire at some point. But the question is, what exactly is an engine misfire, and how does it affect your car? Continue reading the blog to know!

What is an engine misfire?

An engine misfire happens when some parts of the engine fail to make power. It can be caused by things like a dirty spark plug, a faulty oxygen sensor or a clogged fuel injector. If your engine is misfiring, you might notice slower acceleration, shaking while speeding up or the engine might briefly lose power. In this case, you should get the engine checked and fixed quickly, as it can cause major damage.

Ignoring it could lead to expensive repairs, getting stuck on the side of the road or a car accident. Misfires usually turn on the check engine light. They can also make your car use more fuel and produce more emissions because unburned gasoline is coming out of the engine.

What causes misfires?

In the past, spark plugs were the reason for misfires because they only lasted around 12,000 miles. Moreover, they needed frequent replacement due to worn out electrodes, buildup on the electrodes or cracked insulations.

However, thanks to longer-lasting spark plugs with platinum or iridium electrodes, modern ignition systems and computerized engine controls, plugs can last over 100,000 miles. As they wear out, the engine computer adjusts things to prevent deposits from forming.

Even though spark plugs last longer now, they can still wear down or collect deposits that stop them from firing properly. And when that happens, some of the air fuel mixtures might not burn, which can cause a misfire.

Another common cause of the misfire cylinder is the fuel injector. If it gets clogged with dirt or carbon, it cannot deliver enough fuel to the engine. Without fuel, only air goes into the combustion chamber, causing a misfire. Some other possible car misfire symptoms include:

• Problems with the emissions system
• Bad ignition coil
• Vacuum leaks
• Faulty catalytic converter
• Leaking seals or gaskets

Since there are many reasons a cylinder can misfire. That is why it is important to figure out the exact cause before making repairs.

How to tell if car is misfiring?

You can use a scan tool to check the onboard diagnostics system of the car for trouble codes to figure out engine misfire symptoms. Although these codes may not always tell you the exact part that is causing the problem, they can show which cylinder or systems are having issues. A basic code reader that costs around $50 gives less information than the more advanced tools used by professionals.

How to fix engine misfire?

There are different ways to fix a cylinder misfire, depending on what is causing it. Most modern cars have a computer system that stores error codes when a misfire happens. You can start by reading these error codes from the engine as it can help point out the problem.

If the codes are not helpful, mechanics usually check the spark plugs for damage. Black marks or wet spots on the spark plug are signs of damage. If the spark plug is damaged or just old, you can simply replace it to fix the problem. 

Next, mechanics often do a compression test to ensure that the air, fuel and spark systems are working fine. They put a compression gauge in a spark plug slot and start the car. The test results show if the issue is related to compression. If it is, the mechanic might need to fix something like the head gasket, which is a big repair usually best handled by an experienced mechanic.

If there are no compression problems, the issue might be with the coil pack. Mechanics use a multimeter to check if the coil pack is working. They compare the reading on the multimeter to the normal range for that vehicle to see if the coil pack needs to be replaced.

Can you drive with a misfiring engine?

Technically, yes, but it is highly recommended that you do not drive a car with a misfire. Instead, get your car checked as soon as possible. If your engine misfires while you are on the freeway or around other cars, it is best to slow down carefully and move to a safe spot on the side of the road.

If your engine has misfired before and you are not driving it right now, it is best to avoid driving until the problem is found and fixed. While it might be inconvenient, it is much safer than risking the engine failing or getting seriously damaged from repeated misfires while driving.

What are the effects of cylinder misfire on your car?

The most common effect of a misfire is that it will make your car’s fuel efficiency worse. It can also put your safety at risk, as it may cause your car to lose power when you need to pass or avoid a hazard on the road.

In addition to these immediate dangers, misfiring cylinders can lead to serious engine damage if not fixed. Since misfires would not go away on their own and need to be addressed right away. Even if they do not get worse, they will not improve unless a mechanic fixes the issue. 

Driving with a misfire for too long increases the chance of serious engine damage. A misfire usually does not indicate a major mechanical problem and is often caused by something simple like a bad spark plug, ignition coil or fuel injector.

But if you ignore it, more cylinders could fail, and your engine might stop working entirely. To avoid that, it is best to take your car to a mechanic and get it fixed as soon as possible.