6 Engine Misfire Symptoms You Shouldn’t Ignore
Diagnosing the cause of an engine misfire can be difficult, but the context provides important clues. Misfires are often intermittent and may only occur with certain fuel types, environments, or engine loads (how much the accelerator pedal is pressed).
Engine misfire symptoms should not be ignored because cylinder misfires stress the engine and reduce fuel economy over time. The most common signs of an engine misfire are:
What is an engine misfire? A healthy four-stroke internal combustion engine performs a series of actions in the correct sequence and timing to burn fuel and produce power.
1. As the piston moves downward, the intake valve opens, allowing the correct air-fuel mixture into the combustion chamber. After the valve closes, the piston moves upward, compressing this mixture.
2. During the power cycle, this mixture is ignited by the spark plug, further increasing cylinder pressure. This high pressure forces the piston down rapidly, causing the crankshaft to rotate.
3. On the exhaust stroke, the exhaust valve opens, allowing the burnt gases to leave the cylinder, and the cycle repeats.
Misfires are caused by a problem with one or more of the components needed for combustion (fuel, oxygen, spark) or with a mechanical component in the system (such as the cylinder itself). Incorrect ignition timing or one or more cylinders not going through all the steps can cause an engine to misfire. An incorrect air-fuel ratio can cause the mixture not to burn at all or to detonate prematurely (commonly known as knock).
Common Symptoms of an Engine Misfire
An engine misfire, like many other vehicle issues, can cause the same symptoms as other problems. The first step in diagnosing the problem is to see if there are any codes in your vehicle’s computer. If you have one or more of these symptoms, they should alert you to a misfire.
1) Loss of Power, Stuttering, Vibration
- You may be wondering, “What does an engine misfire feel like?”
- You may experience a noticeable loss of power as your vehicle runs on fewer cylinders than normal, or a momentary hesitation in the power delivery when you apply gas.
- You may also experience an intermittent jerking, stuttering, or choppy sound from the engine.
- You will notice jerky or slow acceleration. It is common to experience vibrations while driving a vehicle, especially if the misfire is caused by a mechanical issue. The severity will vary depending on speed, but it is often worse at idle.
2) Strange noises
What does a misfire sound like? When a misfire occurs, the engine makes a sudden, strange noise that can be described as a popping, sneezing, or backfiring. A misfire occurs when unburned fuel leaves a cylinder on the exhaust stroke and is ignited by a spark from the next cylinder further down the system.
Since a 4-cylinder car only has 3 working cylinders, you may notice an overall change in the noise the engine makes if one cylinder doesn’t work at all. It’s like a spark plug has popped out of the cylinder head. You may also hear a vacuum leaking sound in the engine.
3) You have an unusual smell
A misfire can cause an unusual smell because the mixture is incompletely burned. When a cylinder misfires, unburned fuel can enter the exhaust system, causing a strong gasoline smell.
Additionally, if this excess unburned fuel reaches the catalytic converter, it can cause an overload and cause a sulfurous or rotten egg smell because the catalytic converter cannot handle all the hydrocarbons.
4) Check the engine light
Since 1995, vehicles have been equipped with OBD2 systems to help diagnose engine problems. If any of your vehicle’s sensors detect a value other than expected, the check engine light will come on and a code will be stored in the Engine Control Unit (ECU).
Most OBD2 vehicles have a “Cylinder X Misfire” code (where X is the cylinder number that misfired) to help identify the problem. The check engine light may stay on until it is turned off, while some vehicles will have a flashing light when a misfire occurs.
There are many different potential triggers for the check engine light, so it is important to get the code read to pinpoint exactly what has gone wrong. Diagnostic Trouble Codes P0301 through P0312 are some of the more common codes that may appear. The last two numbers indicate which cylinder is misfiring. For example, P0306 indicates a misfire on cylinder 6.
Code P0300 is another code that can occur in conjunction with multiple cylinder misfires. Many car dealerships, like Auto Zone, will do this for you free of charge. Be sure to write down the code and a description of the problem to make troubleshooting easier.
5) Engine Issues
Misfires prevent the engine from operating normally, which can result in a loss of smoothness and consistency in power delivery. If one or more cylinders fail to fire properly, the engine will lose balance in power output and will experience issues, wobbling, or stalling.
This can manifest as a jerky movement when accelerating or the engine not being able to perform as expected, resulting in an overall loss of power. The issue is often most noticeable when the engine is under load, such as when accelerating or climbing a hill, where all cylinders need to fire efficiently to maintain speed and power.
Additionally, misfires can make the vehicle difficult to start or cause the engine to stall when stopped. The latter possibility is even more likely when there are large additional loads (e.g. air conditioning, headlights, radio in use).
6) Excessive exhaust smoke
Black, bluish, or very white sweet-smelling exhaust smoke is a sign that something is wrong. Dark sooty exhaust smoke may indicate a rich mixture or carbon deposits. Bluish exhaust smoke is evidence of burning oil. White, sweet-smelling exhaust may point to a head gasket leak.