9 Common Causes Of Engine Misfires & How To Fix Them

If you have owned a car for any period of time, you have probably heard of the dreaded engine misfire. Perhaps you have even felt a misfire as you were driving your vehicle. Misfires can be difficult to diagnose, and they can be caused by many different things. Today’s car engines are complex, and a problem with any of the systems in your engine can potentially cause a misfire. However, some problems are much more common than others. If you think you might have a misfire, keep reading. We’ll tell you exactly what a misfire is, how to tell if you have one, and the most common causes of the problem.

What Is An Engine Misfire?

An engine misfire occurs when the air and fuel mixture inside the combustion chamber of your car’s engine does not ignite properly or at the right time. To fully understand what a misfire is, it helps to have a basic understanding of how your car’s internal combustion engine works. As the engine runs, your fuel injectors spray the right amount of fuel into the combustion chamber. Your air intake system also allows air to enter the chamber. For your car to run properly, the ratio of fuel to air needs to stay within the proper range. At just the right time, your ignition system will fire and create a spark at the end of your spark plug. This ignites the air and fuel mixture, thus pushing the piston down into the cylinder. This process happens in each of your car’s cylinders thousands of times per minute.

When a misfire happens, this ignition of the fuel does not occur properly. It might mean that the fuel does not ignite at all, so that particular cylinder never fires. Similarly, the fuel might ignite too early or too late. All of these scenarios create a misfire, and it will lead to poor performance from your engine. If the situation gets bad enough, your engine might quit running altogether.

How To Tell When Your Engine Is Misfiring

So, how can you tell when your engine is misfiring? One of the first signs is usually the check engine light. Your car’s computer has sensors that monitor many data points in your car’s engine. The computer is able to tell almost immediately when a misfire happens, and it will illuminate the warning light on your dash to let you know. If you see the check engine light, your local auto repair shop or auto parts store can use a scan tool to confirm that it was a misfire code.

Another way to tell when a misfire occurs is that you can often feel it as you drive. You will usually be able to feel the misfiring engine. It will feel like your engine is skipping or hesitating. You will generally feel it more when the engine is under a load, so press the accelerator pedal a little harder and see if you feel slight skips in the engine running. Lastly, you can sometimes hear the misfires. If your engine is pinging, then it is actually misfiring because the air and fuel mixture is igniting too early. This sounds like a rattling noise coming from your engine, and it also tends to be more pronounced when the engine is under a load.

Common Causes Of Engine Misfires

Now that you know what a misfire is and how to detect one let’s look at the most common causes. Although this is not a list of every possible thing that could cause a misfire, one of the items on this list is usually the culprit.

— Bad Spark Plugs

Bad spark plugs are responsible for misfires in a lot of cases. Spark plugs do not last forever, and they must be replaced when it is time. Generally, spark plugs should be replaced every 50,000 to 100,000 miles. When a spark plug goes bad, it no longer provides a proper spark in the combustion chamber. Without this spark, the fuel will not get ignited properly. This will lead to a misfire every time. If several spark plugs go bad at once, then your engine performance will be extremely poor. Thankfully, the cost of spark plug replacement is not extremely expensive. You can even replace the spark plugs on your own in most vehicles.

— Clogged Fuel Injectors

While many people tend to always think of problems with the spark or electrical system when it comes to misfires, a problem with the fuel can also cause misfires. Clogged or dirty fuel injectors could also be a possible cause. If the fuel delivery is not occurring properly, your engine will not be able to create a proper firing in the cylinder. Buildup in the fuel injectors can lead to rough idling, trouble codes, and misfires. If dirty fuel injectors are your problem, then start with a can of fuel system cleaner. This can be an inexpensive and easy way to fix the problem.

— Ignition System Problems

Similar to bad spark plugs, a problem with your ignition system will lead to a lack of proper spark. It could mean that the spark never even makes it to the spark plugs. It could also mean that the timing of the spark is wrong. Ignition system problems could be anything from bad ignition coil packs to a loose distributor cap. Spark plug wires can also go bad and prevent the electrical current from making its way to the spark plugs. A car repair shop can usually use a code reader to pinpoint the problem with your ignition system.

— Dirty Fuel Filter

A dirty fuel filter can cause many problems, and misfires are one of those. A clogged fuel filter can lead to low fuel pressure, and it can prevent the proper amount of fuel from making its way to the combustion chamber. This can result in a loss of power, cylinder misfires, and other problems. It could even cause problems with your fuel pump. While you can try a fuel system cleaner to correct the problem, it’s likely that you need to replace the fuel filter. It’s a fairly simple job that most automotive repair shops can perform within an hour or two.

— Vacuum Leak

There are many vacuum hoses routed around your intake manifold that control airflow to various parts of your engine. These hoses need a proper seal to successfully pull a vacuum and control the airflow properly. A leak in one of these hoses can wreak havoc on the entire system. It can lead to a rough idle, misfires, and other issues. A bad or leaking manifold gasket can also cause similar issues.

— EGR Valve

Many people are not familiar with the function of their car’s EGR valve. The valve allows exhaust gasses to recirculate through the manifold. This helps with emissions and keeping your car running properly. However, this valve can become clogged and stop operating properly. When that happens, your vehicle can begin to starve for air in some cases. This will lead to a misfiring engine if not corrected.

— Catalytic Converter

A dirty or clogged catalytic converter can lead to engine misfires, although that is not usually the first sign of a bad catalytic converter. When the converter becomes clogged, the pressure in the exhaust system builds beyond what is normal for your vehicle. This can prevent the exhaust gasses from properly exiting the combustion chamber, and this will lead to misfires. For most issues, a can of catalytic converter cleaner will take care of the problem. However, for severely clogged converters, you will need a replacement. Replacing a converter is not cheap, as the part itself can sometimes cost over $1,000.

— Worn Piston Rings

As the engine’s crankshaft spins, the pistons move up and down in the cylinders. As the cylinder compresses the air inside the cylinder head, pressure starts to build. If the piston rings are bad, a proper seal is not formed along the cylinder wall. This leads to low compression because the pressure cannot be held inside the cylinder. Low compression will lead to misfires and poor engine performance. A mechanic can perform a quick compression test to determine whether this is the cause of your problems. A blown head gasket can also present similar symptoms, although you will usually start to notice a mixing of your oil and coolant in that case. Blown head gaskets also lead to frequent overheating of your car’s engine.

— Computer Issues

As we previously mentioned, your car’s engine has many sensors that are tied to the vehicle’s main computer. Any glitches or problems in the sensors, computer, or software will lead to big problems. A failure of the computer to send the proper signal can result in an engine misfire. You might simply need to have your car’s computer reflashed with new software. In more serious cases, you might need to replace the computer. Replacing the car’s computer module can be costly, so you should make sure that you use a trusted mechanic for the job.

Diagnosing & Repairing The Cause Of The Misfire

Finding the exact cause of a misfire can sometimes be challenging, although the best place to start is usually a scan tool. These tools will read the trouble codes from your car’s computer, and they generally will give you quite specific codes that reveal the cause of the problem. In that case, you should know exactly what is causing the misfire. However, sometimes the codes are more generic. If the code only tells you that you have a misfire in a particular cylinder, you should first start with the easy and cheap items.

You should first examine the spark plug in that cylinder. If that doesn’t fix the problem, then spark plug wires and coil packs are likely the next best steps. If neither of those fixes the issue, then it might be time to let a mechanic step in. They can generally provide more expertise and help track down your problem so you can get it corrected.

The Bottom Line

Engine misfires can be caused by many different problems, but the fix is usually a simple one. Replacing spark plugs or cleaning your fuel injectors will often correct the problem. However, you might need a scan tool to read the trouble codes from your vehicle’s computer to help with more complex issues. The codes stored in the computer will give you much more insight into the cause of the problem. Once you have it fixed, your engine should continue running smoothly!

Frequently Asked Questions

Can you drive a car with an engine misfire?

In most cases, you can drive a car with a mild engine misfire. However, you will start to notice a decrease in performance. If the engine misfire gets bad enough, the car could stall or quit running altogether. If you notice the car running rough, you should stop driving it until you can get the issue corrected. While it is not likely to do any further damage to the engine most of the time, it could put you in danger while driving the vehicle in traffic.

How much does it cost to fix an engine misfire?

The cost to repair the misfire depends on the specific cause of the problem. If you only need to replace a single spark plug, the repair can be performed yourself for as little as $5 in some cases. However, if you have bigger issues like ignition system problems or a clogged catalytic converter, you will likely have a repair bill of several hundred dollars. Before determining the cost of the repair, you will need to fully diagnose the problem.

How does an engine misfire happen?

An engine misfire happens when the air, fuel, and spark inside the combustion chamber do not come together properly. This means that the proper amount of air and fuel must be inside the chamber from the intake and fuel injectors. Similarly, the ignition system must deliver the spark, and the spark plug must fire at precisely the right time. A problem with any of those things will lead to a misfire.