You’re headed to work or running some errands when suddenly, your car starts to shake and sputter. The dreaded “Check Engine” light rears its ugly head, and you can’t help but worry about what’s happening under the hood of your vehicle.
Chances are, you’re experiencing an engine misfire, a common issue that affects many cars on the road today.
But what exactly is a misfire? What does it feel and sound like? And most importantly, what causes a misfire in the first place?
What Is a Misfire?
An engine misfire is when one or more engine cylinders fail to properly combust the air-fuel mixture, causing a loss of power and stumbling sensation from the engine. The car will still be able to run and you’ll be able to drive it, but you’ll start to notice the engine jerking.
This could be followed by exhaust smoke coming out of the tailpipe, the smell of gas, and loud popping sounds. When you experience these symptoms, you likely have an engine misfire (aka cylinder misfire).
Misfires reduce engine performance and efficiency and if you let them go on for too long, it can end up damaging your engine or catalytic converter.
What Does an Engine Misfire Feel Like?
An engine misfire will be recognizable to the driver because their engine will feel like its stumbling for a few seconds and then regain its pace again. The number of times this happens will depend on the seriousness of the misfire.
If at least one spark plug is not firing correctly then it will cause the engine to malfunction and run terribly. The car may still move, but you will notice an increase in your vehicle’s exhaust emissions, a lack of acceleration and a reduction in the engine’s power.
If you step on the gas pedal and it takes awhile for your car to go faster while leaving behind a cloud of smoke behind you, this probably means you have a misfire.
At this point, your engine will require more fuel than necessary just to operate at its normal level. This will result in you having to spend more money on gas.
What Does a Misfire Sound Like?
The best way to describe the noise a cylinder misfire makes is to think of popcorn kernels randomly popping. In some vehicles it can also sound like a “chug” or sneeze.
While a backfire is technically different than a misfire, a loud “bang” or “poot” can be heard from both.
Top 5 Reasons Your Car Misfires
There are lots of reasons as to why a car would misfire in the first place. To help you understand what might have been the cause of your car misfire, below are five of the most common causes that someone could experience in this situation.
1) Air to Fuel Ratio Imbalance
One of the main reasons for an engine misfire can be attributed to an imbalance in the air to fuel ratio within the internal combustion chamber. This usually means there is not enough fuel and too much air being mixed together.
For the combustion to be successful, the mixture needs a specific proportion of fuel for the amount of air entering the engine. Otherwise, you will notice the cylinder misfire while your engine is idling. But when you’re driving at faster speeds, the symptoms of the misfire will go away.
2) Ignition System Issues
There could be a problem coming from any one of the components in the ignition system. Perhaps the spark plugs aren’t creating an adequate spark for the internal combustion chamber.
You could also have a worn-out ignition coil, ignition cables, rotor, or distributor cap. If any of these problems exist, the internal combustion chamber’s air and fuel mixture won’t be able to ignite properly.
The weak spark will cause an engine misfire, but you might not notice right away. But as you operate the vehicle, you’ll feel its jerkiness very well.
3) Transmission Issues
There are times when the misfire might not even come from your engine. It could come from the transmission instead. If your car starts to jerk around like an engine misfire had occurred, your transmission may not be able to adequately shift up or down.
You will notice this more when you’re driving at faster speeds. This is a bad situation like any other misfire and you need to have it repaired right away.
4) Mechanical Problems
Your vehicle is made up of many mechanical parts which contribute to the functionality of the engine. There are piston rings, camshaft lobes, valves, and cylinder walls.
If any of these parts were to get worn out, it could cause an engine misfire. The same goes for when there’s an intake manifold gasket leak or a head gasket leak.
Other possible mechanical issues may include a bad fuel injector or damaged rocker arms. Check the timing belt to see if that’s installed correctly too because it may have slipped.
You will know when there’s a misfire caused by mechanical issues because there will be a thumping feeling from the vehicle that will never go away, regardless of your speed.
5) ECM Problems
Sometimes there may be a glitch in the engine control module or the central computer of the vehicle which manages the engine. Any minor glitch there could throw off the combustion process and cause a misfire.
Fortunately, there is an easy remedy to this type of problem that works most of the time. If you simply disconnect your battery for a few minutes and then reconnect it. It’s similar to rebooting a computer at home and this should solve any minor glitch or bug in the computer system.
If the bug still exists after that, then you need to have the central computer examined at the dealership where you got the car.
Symptoms of an Engine Misfire
When your engine starts to misfire, you’ll notice a few key symptoms. It’s important you pay attention to these and not ignore them or a little problem now can turn into an expensive repair if left unchecked.
- Shaking – One of the first things you might feel is a shaking sensation throughout the vehicle. This can be due to the uneven firing of the cylinders in your engine.
- Rough Idle – If your car is idling roughly, you may notice it vibrating more than usual. This can be a telltale sign of an engine misfire.
- Flashing Check Engine Light – A flashing (not steady) check engine light can indicate that your engine is misfiring. This can be a red flag, especially when combined with other symptoms.
- Rough Acceleration – Another sign of a misfiring engine is rough acceleration. If your vehicle feels like it’s jerking, this can be an indication of an engine problem.
- Loss of Power – A misfiring engine can lead to a loss of power in your vehicle as it struggles to maintain proper combustion.
- Popping Sounds – Popping or backfire sounds coming from your engine can be a symptom of an engine misfire. This is due to the uneven combustion of fuel in the engine.
- Fuel Smell – While not a direct symptom, it strong gasoline smell is a sign of an underlying issue from improperly burned fuel which is causing the misfire.
- Exhaust Smoke – If you notice excessive exhaust smoke, it could be a sign that an engine misfire is causing unburned fuel to be released into the exhaust system.
Can a Misfire Go Away On Its Own?
Sometimes, a misfire can go away on its own, especially if it’s caused by a temporary issue like bad fuel or moisture in the ignition system. However, relying on the misfire to resolve itself isn’t the best approach. In most cases, it’s better to address the underlying cause instead of waiting for it to go away.
For instance, if you suspect bad fuel is causing the misfire, try filling up with a higher-quality fuel next time or use fuel additives to clean your fuel system.
What Does It Mean When the Misfire Goes Away When Accelerating?
When a misfire goes away while accelerating, it typically indicates the root cause is a fuel delivery problem rather than an ignition problem. This could mean that there is a problem with the fuel injectors, fuel pump, or fuel pressure regulator, which are responsible for delivering the right amount of fuel to the engine.
When the engine is idling or running at a low speed, there may not be enough fuel reaching the cylinders, causing a misfire. However, when the accelerator is pressed, more fuel is delivered to the engine, which can help compensate for the lack of fuel and eliminate the misfire.
How Much Does It Cost to Fix an Engine Misfire?
The cost to fix a misfire mostly depends on the CAUSE of the misfire. For that reason, the cost to repair a misfiring engine can range anywhere from $120 or so to $3,000 for more serious issues like damaged piston rings. But let’s break it down a bit more to a sampling of causes to give you a better idea of what you might be dealing with. Costs below include labor.
- Ignition Coil Replacement: $200 to $300
- Spark Plug Replacement: $300 to $800 (for a full set)
- Distributor Replacement (if your car has one): $250 to $500
- Valve Adjustment: $125 to $300
- Fuel Injector Replacement: $200 to $500
- Spark Plug Wire Replacement: $120 to $300
- Crankshaft Position Sensor Replacement: $120 to $260
Please note that these costs will vary based on your location, make and model of car, and where you take your vehicle to get serviced (a dealership will likely cost more than an independent mechanic).
How to Identify the Misfiring Spark Plug
If you’ve determined that a spark plug is causing the misfire, here is a step-by-step procedure for identifying which exact spark plug is the culprit:
- Visual Inspection – Remove all the spark plugs one by one and examine their condition. Look for any cracks, excessive wear, fuel fouling, oil fouling, or corrosion on the plugs. This can identify any damaged plugs.
- Spark Test – With the engine off, reinstall one spark plug at a time and ground the plug on the engine block. Have someone crank the engine while you observe the spark at the grounded plug. No spark indicates a bad plug.
- Switch Coils/Plugs – If all plugs are sparking properly, swap ignition coils and plugs between different cylinders. For example, switch coil 1 with cylinder 2. If the misfire moves to cylinder 2, then the issue is with coil 1.
- Check Resistance – Use a multimeter to check plug wire resistance. Compare readings across all plug wires. Higher than normal resistance in one wire indicates a problem with that plug or wire.
- Compression Test – Run a compression test on each cylinder. Lower compression in one cylinder indicates an issue with that piston/ring assembly that could cause a misfire.
- Add Fluorescent Dye – Add fluorescent dye to the suspected cylinder’s spark plug hole. Run the engine and inspect each plug. The plug from the misfiring cylinder will have no dye traces if the issue is with that plug or wire.
Following this systematic process should isolate the problematic spark plug and allow it to be replaced to cure the misfire.