What Causes Engine Misfires and How Can You Identify Them?

What does “engine misfire” mean?

An engine misfire happens when the cylinders in the engine don’t burn right or the combustion within the chamber is incomplete (or nonexistent!). Typically, engine misfires can be caused by a variety of factors, including malfunctioning coils, worn or faulty spark plugs, a leak or a faulty ignition switch. 

Here are just a few common causes of engine misfires:

Common Causes of Misfires

Ignition Trouble

In most cases, a worn-out spark plug is to blame for an engine misfire. Spark plugs play a key role in igniting the fuel in the engine. When a spark plug is worn out or bad this process cannot take place, leading to engine misfires. 

It’s also important to keep in mind, however, that spark plugs are only once piece of the larger ignition system. Issues with any components — coil packs, wiring, control module, etc. — within the ignition system can cause an engine misfire. 

Mechanical Error

Another cause of a misfire may be due to mechanical failure within the engine. Issue with components of the engine that keep the cylinders from sealing properly can lead to poor compression and poor burn, thus resulting in an engine misfire. 

Emissions Equipment Problems

Engines have a specific air/fuel mixture that is crucial for combustion. Most modern vehicles have complex equipment meant to release exhaust and emissions, the result of combustion, back into the atmosphere. If this equipment malfunctions and leaves emissions in the engine, it can mess with the air/fuel mixture, leading to a misfire.

Diagnosing An Engine Misfire

All this information about engine misfires isn’t actually helpful unless you’re able to tell when a problem is occurring. 

What does engine misfire feel like?

An engine misfire can feel slightly different depending on the type of problem occurring. Generally speaking, though, one of the most common signs of a misfire is hesitation or loss of power during acceleration. 

When you first turn your car on or once you start moving after coming to a stop at a light you may notice that your vehicle is having a rough time idling. If your engine is unbalanced as a result of a misfiring cylinder you may experience shaking. A vehicle that is misfiring may be jerky or shake violently. You may also experience stalling when running the A/C or lights throughout the car. 

What does an engine misfire sound like?

Another way to diagnose an engine misfire is by sound. Engine misfires have a very distinct sound that can make them easier to diagnose than other car problems. 

Popping, sneezing, or banging sounds coming from the exhaust are a sign of a misfire. This sound comes from the unburnt fuel leaving the cylinder that combusts through the exhaust system. 

What are the dangers of engine misfire?

Engine misfires can lead to huge problems if not addressed quickly. Any of the causes of a misfire can have drastic consequences and have the potential to cause irreversible lead to an overheated engine or a damaged catalytic converter (we discuss the importance of your catalytic converter in this previous blog post). 

If your vehicle is experiencing mystery engine misfires, you want to get it serviced immediately. Waiting to take your vehicle in can put your vehicle, yourself, and other drivers at risk. When you come in, make sure to let your technician know what kinds of issues are going on (sounds, how it runs, etc.). This may help them identify the issue. 

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