9 Engine Misfire Symptoms & Diagnostic

Engine Misfire Symptoms

An engine misfire is a common problem that affects many vehicles, and it occurs when one or more cylinders fail to ignite fuel properly.

This can result in various issues affecting the engine's performance, fuel efficiency, and longevity. Recognizing the signs of a bad engine misfire ensures your vehicle runs smoothly and efficiently.

If not addressed promptly, engine misfires can lead to more severe problems, such as damage or complete failure.

In this article, we will explore the various bad engine misfire symptoms, the causes behind this issue, and the steps you can take to diagnose and repair it.

Additionally, we will discuss preventive measures that can help you avoid engine misfires in the first place.

Engine Misfiring - Spark Plug or Ignition Coil Video

Causes of Engine Misfire

Engine misfires can be caused by various factors, from spark plugs and ignition systems to fuel injectors and internal engine parts.

Here are some of the most common causes of engine misfires, according to cars.com:

1. Spark Plugs

Historically, they were a common cause of misfires due to their short lifespan.

With modern electronic ignition systems and computerized engine controls, spark plugs last much longer.

However, they can still wear out and collect deposits that prevent them from firing at full strength, leading to a misfire.

2. Fuel Injectors

Fuel injectors can become clogged with dirt or carbon or fail for other reasons.

When this happens, they can't deliver fuel to the combustion chamber, resulting in a misfire.

3. Ignition Coil Packs and Wires

Each cylinder has an ignition coil pack that sends electricity to the spark plug, igniting the air-fuel mixture. These coil packs and wires can wear out or fail, leading to a misfire.

4. Vacuum Leaks

Engines have many small vacuum hoses that allow airflow. A tiny pinhole in one of these hoses can cause the engine computer to receive incorrect information, resulting in a misfire.

5. Emissions System Parts

Various emissions controls inform the engine computer about how much air and fuel goes into the engine and when spark plugs should fire.

A faulty oxygen sensor, clogged or failed exhaust gas recirculation, or crankcase ventilation valve can send incorrect signals to the computer and cause misfires.

6. Catalytic Converter

A clogged catalytic converter can cause problems upstream, such as overheating or misfires.

7. Internal Engine Parts

Seals and gaskets are essential in maintaining optimum compression and keeping air and fluids flowing where they should.

Leaks in valve seals, manifold gaskets, worn valve guides, or broken piston rings can reduce engine power and cause misfires.

Engine Misfire Symptoms

When it comes to engine misfires, there are a few telltale signs that can help you identify the problem.

According to vehq.com, one of the most common symptoms is a noticeable shake or vibration in the car when driving.

1. The car Becomes Unbalanced

It can feel like the vehicle is unbalanced or running rough. This can be particularly noticeable when accelerating or when driving at higher speeds.

2. Engine Light Coming On

Another sign that your car may be experiencing an engine misfire is the check engine light coming on.

The check engine light is a warning system designed to alert you to potential problems with your vehicle.

Paying attention to this warning and having the car inspected immediately is essential.

3. Sluggish Response

When you try to accelerate, you may notice that the response is sluggish or that the car is running rough.

This can indicate an engine misfire, as the combustion process in one or more cylinders is not working correctly.

4. Sounds From the Engine

Sounds coming from the engine can also indicate an engine misfire. You may hear clanking, sputtering, popping, or other unusual noises.

5. Smoke

In some cases, you may also notice black smoke coming from the exhaust pipe.

This is because of unburned fuel entering the exhaust system and is a sign that something is not working correctly in the engine.

6. Clunky Idling

Another common symptom of an engine misfire is rough or clunky idling. This means that when the car is stationary and the engine is running, it feels like it's struggling to maintain a steady idle speed.

This can be particularly noticeable when sitting at a stoplight or in heavy traffic.

7. Underperformance When Driving

You may also notice a need for more power or underperformance when driving.

This can be frustrating, as the car may respond differently when you try to accelerate or climb a hill. Sometimes, you may even smell gasoline, oil, or coolant.

8. Engine Stalling

Engine stalling is another symptom that can occur when there is an engine misfire.

This means that the engine shuts off unexpectedly, which can be dangerous if you're driving on the road.

9. Poor Gas Mileage

Finally, poor gas mileage can indicate your car is experiencing an engine misfire.

If you notice these symptoms, taking your car to a qualified mechanic is vital for a proper diagnosis.

Ignoring the problem can lead to further damage to your vehicle and even be dangerous if the car stalls unexpectedly.

A professional mechanic can determine the root cause of the engine misfire and make the necessary repairs to get your car running smoothly again.

Diagnosing Engine Misfire

Diagnosing an engine misfire can be a challenging task for many car owners. The process requires technical knowledge and tools that may be limited to the average person.

But if you suspect your engine is misfiring, taking it seriously and diagnosing the problem immediately is essential.

A misfiring engine affects your car's performance and can lead to more severe and costly damage if left unchecked.

According to axleaddict.com, there are several steps in diagnosing an engine misfire. These steps include:

1. Checking for Trouble Codes Using a Scan Tool

The first step in diagnosing an engine misfire is to check for trouble codes in the car's onboard diagnostic system.

Trouble codes will help you identify the specific cylinder or cylinders that are misfiring and any other methods that may not function correctly.

If you don't have a scan tool, you can take your car to a mechanic or an auto parts store to have the codes checked.

2. Inspecting the Spark Plugs

The spark plugs are a critical component of your car's ignition system, and worn or faulty spark plugs can cause misfires.

Checking the spark plugs involves removing them from the engine and examining their condition.

If the spark plugs look worn, damaged, or covered in deposits, they may need replacing.

3. Checking the Ignition Coils

The ignition coils supply electrical power to the spark plugs. If the coils are faulty, they may not deliver enough power to the plugs, causing misfires.

Testing the ignition coils involves using a multimeter to check their resistance and ensure they receive the correct voltage.

4. Testing the Fuel Injectors

The fuel injectors deliver fuel to the engine's cylinders. Clogged or faulty fuel injectors can cause misfires by preventing the proper amount of fuel from reaching the cylinders.

Testing the fuel injectors involves using a fuel pressure gauge to check the fuel pressure and ensure that the injectors deliver fuel correctly.

5. Checking for Vacuum Leaks

Vacuum leaks can cause misfires by allowing unmetered air into the engine.

Checking for leaks involves inspecting the hoses and connectors for damage or cracks and using a smoke machine to detect leaks.

6. Inspecting the Compression

The engine's compression is essential for proper combustion, and low compression can cause misfires.

Examining the compression involves using a compression gauge to check the pressure in each cylinder.

7. Checking the Timing Belt

The timing belt synchronizes the engine's valves and pistons. If the timing belt is damaged or worn, it can cause misfires.

Checking the timing belt involves inspecting it for signs of wear or damage and ensuring it is properly tensioned.

Engine Misfire Repair Cost

The cost of repairing an engine misfire varies and depends on what's causing the issue.

According to howmuchisit.org, the cost can range from as little as $150 for new spark plugs to as much as $1,000 or more for a vacuum leak.

Here's a breakdown of estimated costs for some common causes of engine misfires:

  • Bad fuel delivery: $200 to $1,000 or more, depending on the reason for the bad fuel delivery.
  • Bad spark plug wires: $100 to $300.
  • Broken piston rings: $1,500 to $3,000.
  • Broken valve springs: $450 to $650.
  • Carbon or oil-fouled spark plugs: $100 to $250, depending on the costs of the plugs and local labor rates.
  • Faulty ignition coil: $150 to $250.
  • Fuel injector: $275 to $400.
  • Vacuum leak: $200 to $800.

It's important to remember that these are just estimates, and actual costs may vary depending on the problem's severity, the vehicle's make and model, and local labor rates.

If you're experiencing an engine misfire, having a professional mechanic diagnose the issue and accurately estimate the necessary repairs is best.


An engine misfire is a problem that occurs when one or more cylinders in an engine fail to function correctly.

This can lead to a range of issues, including reduced power, decreased fuel economy, and even damage to the engine over time.

Engine misfires symptoms can vary and can lead to problems with fuel delivery, issues with ignition systems, or mechanical faults within the engine.

It is crucial to address an engine misfire promptly to avoid further damage and restore proper engine function.