What Happens When a Car Misfires?

Dustin Hawley | Feb 12, 2021

At some point in time or another, we’ve all seen at least one car on the road with black smoke streaming from its exhaust pipe. For those who have driven older model vehicles, you may have some familiarity with an engine “coughing” suddenly, causing the car to sputter and slow. In both of these cases, the culprit was likely an engine misfire.

what causes car to misfire

But what exactly happens when a car misfires, and what does it mean for the health of your engine?

What Is A Misfire?

For your engine to fire its cylinder, it relies on three main components. It needs fuel to burn, oxygen to facilitate the burn reaction, and a spark to get things going. If any of those elements are not present at the perfect time, the cylinder won’t combust. It won’t start the chain reaction that leads to a well-running engine.

At its core, an engine misfire occurs when the combustion reaction doesn’t work correctly, and your cylinder remains unfired. Misfires can occur both upon engine startup and even in the middle of engine idling.

When a misfire happens, your engine might momentarily stumble, and it may even lose speed (RPMs). However, most misfires dissipate, and your engine regains its normal speed after a second or two. But even a single misfire is usually a sign that something else is wrong and that more misfires will likely occur in the future.

Furthermore, misfires are taxing on your car’s engine. Multiple misfires can put a mechanical strain on various engine components, potentially leading to other issues later down the road.

How Do Misfires Happen?

A misfire can occur due to a malfunction or problem with any of the components mentioned above as it relates to your internal combustion reaction.

Spark Misfires

As the name may imply, spark misfires usually happen when there’s a problem with your spark plugs, which are the small parts in your engine that ignite and begin the combustion reaction that produces engine power. 

Fortunately, you can find replacement spark plugs for cheap and can likely even swap them out yourself in just a few minutes with a simple tutorial. However, you should also make sure that the ignition wires connected to the spark plugs are in good condition. If they look worn down or old, you should replace them.

Fuel Misfires

Your fuel system can also be a culprit of engine misfires. For example, if your fuel filter is clogged, it can prevent an adequate amount of fuel from reaching the cylinder for ignition. In some cases, your fuel cylinders may also be dirty.

As opposed to the other types of misfires, fuel-related misfires can occur suddenly and usually happen when you are idling instead of driving at regular speeds.

Mechanical Misfires

Mechanical misfires are potentially the most complex and damaging of all three types of misfires. They can occur when, for instance, the timing belts or chains under the hood of your car slip, disrupting the internal combustion process. Your valvetrain could also be damaged, or your vacuum lines could be compromised or worn down with time.

Regardless of the specific cause, mechanical misfires are the most serious in regards to how they need to be addressed because they aren’t merely going to go away in due time. Instead, they will likely fester and only worsen, leading to other engine damage if left untreated. If you are experiencing a mechanical misfire, we suggest you immediately take your car to a certified mechanic. 

Symptoms Of A Misfire

Regardless of the type of misfire, you’ll probably experience a few shared symptoms that are common with misfiring.

Rough Idling

Engines that idle in a clunky or rough manner could be suffering from misfiring. In essence, when a misfire occurs and the air to fuel mixture in the cylinder becomes compromised, your engine essentially may jump up and down, causing your car to start and stop suddenly. This will likely lead to a bumpy driving experience, and another common symptom of this type of misfire is the smell of fuel in the cabin.

Sluggish Acceleration

Your car might have trouble reaching adequate speeds if your engine is misfiring. In fact, misfires occur most frequently when your vehicle is under load and continuously accelerating. 

Any response to engaging acceleration may be sluggish or slow. Alternatively, you may experience a jerking motion when you step on the gas. When this occurs, it can be hazardous to both yourself and other drivers at risk.

Engine Sound Changes

If you are experiencing misfires, you might also hear sudden changes in your engine’s sound. If you think you may be hearing odd sounds emitting from your engine bay, turn your radio off and listen for any clanking, coughing, or sputtering. Any of these types of sounds could possibly be signs that your internal combustion reaction has been interrupted due to a misfire.

It’s common sense in any case. If your engine sounds “off” in any way, you need to have it inspected by a certified mechanic as soon as possible.

Black Exhaust

When your engine misfires, it might create a cloud of thick, black exhaust, which is often a sign that your engine is not passing fuel and air correctly. If you find that your vehicle is emitting exhaust in this fashion, you may be experiencing a misfire.

Your “Check Engine” Light Might Illuminate

Lastly, engine misfires frequently cause your “check engine” light to illuminate. Many modern vehicles have specific built-in sensors that can monitor your engine’s performance. While they may not be able to tell you that a misfire has explicitly occurred, they will tell you that your engine is not functioning correctly and needs to be examined by a professional.

Can You Drive With A Misfiring Engine?

Technically, yes. However, it is strongly advised that you don’t. Instead, you should look to have your car inspected as soon as possible.

If you experience an engine misfire while you are on the freeway and/or surrounded by other cars, it is best to slowly and carefully get to safety first and try to cruise your vehicle to the side of the road. 

However, if your engine has misfired in the past and you aren’t currently driving it, you should avoid driving the vehicle until you have identified and fixed the root problem. While it may be inconvenient, it’s far better than having your engine suddenly quit or suffer catastrophic damage because of repeated misfires while on the road.

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