A cylinder misfire is a common problem that can happen for a variety of reasons. When your car starts misfiring, you’ll likely notice engine performance problems, such as rough running and hesitation. The check engine light will usually illuminate, as well.
Not only does a misfire make your car unpleasant (and sometimes unsafe) to drive, but it can also cause additional damage to your vehicle. So, you’ll definitely want to diagnose and repair the problem right away.
What is a Cylinder Misfire?
To understand a misfire, it helps to first have knowledge of how a gasoline engine creates energy by compressing and igniting an air-fuel mixture.
When the engine is running, a series of valves allow air (and fuel in the case of port injection) to enter each cylinder in sequence. After air and fuel have been pulled into one of the cylinders, the valves close and the piston moves upward in that cylinder to pressurize (compress) the mixture.
Next, the spark plug fires and the air-fuel mixture is ignited. The explosion (combustion) forces the piston downward, causing the crankshaft to turn. The process is repeated in each of the engine’s cylinders to create the rotational force needed to propel your vehicle down the road.
A misfire occurs when there’s incomplete (or zero) combustion taking place inside one of the engine’s cylinders. On a modern car, the problem will almost always trigger the check engine light. You might also notice that the engine runs rough, hesitates, or lacks power (or suffers from all three issues).
What Causes a Cylinder Misfire? Common Causes
An engine needs three primary ingredients to run properly: a precise air-fuel mixture, adequate spark, and good compression. When one or more of these factors are missing, incomplete combustion occurs, resulting in a misfire.
There are many potential engine misfire causes. Here are some of the most common:
Ignition System Problems
Ignition system problems that result in inadequate or improperly timed spark cause an engine misfire. Some examples include:
Air-fuel Mixture Issues
Any problem that throws off the engine’s air-fuel mixture can result in a misfire. Some examples include:
- Vacuum leaks (allowing unmetered air to enter the engine)
- Faulty fuel pump
- Bad or dirty fuel injectors
- Failed fuel pressure regulator
- Clogged fuel filter
Engine Mechanical Problems
A variety of engine mechanical problems can result in a loss of compression, causing a misfire. Some examples include:
- Worn pistons, rings, or cylinder walls
- Blown head gasket
- Damaged valves and valvetrain components
- Worn timing belt or timing chain
Sensor and Module Issues
Your car’s engine computer, which is often referred to as the powertrain control module (PCM), receives input from a wide range of sensors. The module then uses that information when deciding how to operate output devices, such as the ignition coils and fuel injectors.
Many of the sensors the PCM relies on can cause a misfire when they fail. The module itself can also cause a misfire if it has an internal failure, such as a bad coil or injector driver. Some examples of sensor and module issues include:
- Bad sensor (e.g., mass airflow or crankshaft position sensor)
- A PCM hardware or software failure
- Circuit issues, such as damaged wires and poor connections
Other Systems Failures
But wait—that’s not all. Modern vehicles are fitted with other engine-related equipment that can lead to a misfire when it fails. Some examples include:
- Exhaust gas recirculation (EGR) system problems
- Cylinder deactivation system problems
- Variable valve timing system problems
- Secondary air injection (SAI) system problems
How much is it to fix an engine misfire?
Exactly how much it costs to fix a misfire will depend on what’s causing the misfire to begin with. The issue can result from something as inexpensive as a spark plug or as costly as an internal engine failure. Usually, a repair shop will charge between $100 and $200 to diagnose the problem.
How long can you drive with a misfire?
A misfire can eventually damage the catalytic converter and possibly even the engine itself. As such, you’ll want to diagnose and repair the problem right away.
How do you diagnose a misfire?
Diagnosing a misfire can be difficult, especially if the problem is occurring on more than one cylinder. If you’re not particularly confident in your troubleshooting skills, you might want to leave the job to a professional. Otherwise, you can check out the videos below for an idea of what the diagnostic process might involve:
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic.