Going on a spontaneous road trip is always fun except when you run into performance issues that you didn’t expect. While they can be caused by something as simple as a loose gas cap, they can also be indicators of more serious problems like a busted radiator or a blown head gasket.
In some cases, poor performance can be a sign that your engine is misfiring. This calls for an immediate trip to the nearest repair shop.
But what exactly does a misfiring engine mean? Let’s find out.
What Is a Misfire?
An engine misfire occurs whenever there’s a problem with the combustion process. More specifically, when there’s incomplete or zero combustion inside one or more cylinders. When the combustion reaction doesn’t work as it should, the cylinders remain unfired, causing your vehicle to stumble, lose speed, or exhibit other symptoms of engine performance problems.
Vehicles equipped with an OBD-II system usually come with a misfire monitor. The powertrain control module (PCM) uses the information from the crankshaft position sensor to calculate the time between the edges of the reluctor, rotational speed, and acceleration. By comparing the acceleration of each firing event, the PCM can detect whether or not a cylinder is firing correctly.
The misfire monitor looks out for two types of engine misfires.
Misfire Type A
Misfire Type A occurs at 200 revolutions. Once this type has been detected, the check engine light will blink once per second during the misfire and the computer will store a diagnostic trouble code (DTC). This type of misfire can also cause catalyst damage, which is why it’s important to have your vehicle checked by a certified mechanic as soon as this happens.
Misfire Type B
A Misfire Type B occurs at 1,000 revolutions. This type exceeds 1.5 times the US Environmental Protection Agency (EPA) federal test procedure (FTP) standard and might cause your vehicle to fail its emissions test.
Understanding the Combustion Process
To further understand the concept of a misfiring engine, let’s take a closer look at the combustion process.
Most modern vehicles are equipped with an internal heat combustion engine where combustion occurs inside the power chamber. This is where the chemical energy of gasoline is converted into heat. As heat energy causes the temperature of combustion gases to increase inside the chamber, the pressure of these gases also increases. The pressure buildup inside the chamber is then applied to the head of a piston to produce a usable mechanical force, which is converted into mechanical power.
As the piston moves downward, it draws the air-fuel mixture into the cylinder through the intake valve on the intake stroke. As it moves upward, the mixture is compressed on the compression stroke with both valves closed.
The ignition occurs at the beginning of the power stroke, and the combustion moves the piston downward to produce power. The upward-moving piston then forces the burned gases out of the open exhaust valve on the exhaust stroke.
What Happens When a Car Misfires?
Most of the time, a misfiring engine will lead to various performance problems. Here are the most common engine misfire symptoms you should look out for.
Illuminated Check Engine Light
An illuminated check engine light is the most common indicator of engine-related problems, which is why it’s important to have your vehicle checked by a certified mechanic as soon as this light pops up on your dash.
Poor Acceleration
Poor acceleration or a jerking motion whenever you step on the gas pedal can also be a symptom of a misfiring engine. In most cases, the misfire will happen during constant acceleration or whenever your vehicle is under load.
Rough Idling
Improper air-to-fuel mixture can cause your vehicle to jump up and down, leading to an uncomfortable driving experience.
Engine Noises
Clanking, coughing, and sputtering noises from the engine bay could indicate a misfiring engine.
Black Smoke in the Exhaust
A misfiring engine can also cause your vehicle to emit black smoke from the exhaust, which is a sign that the engine is not passing air and fuel correctly.
Note: A misfire can happen momentarily. Afterward, your vehicle could regain its normal speed and perform as it should. However, keep in mind that once a misfire occurs, it’s bound to happen again, but causing more damage to various parts of the engine.
Causes of an Engine Misfire
Several damaged or broken parts can lead to an engine misfire, and these components tend to come from different systems.
Ignition System Problems
An ignition misfire due to a defective spark plug wire, pickup coil, module, and poor electrical connections cause no burned air and fuel to be exhausted past the oxygen (O2) sensors, leading to a misfire.
Air-Fuel Mixture Problems
A lean air-fuel mixture can also cause a misfire. This problem usually occurs when there is low fuel pump pressure, a clogged fuel filter, or a restricted fuel injector.
Mechanical Issues
Worn pistons, rings, cylinder walls, timing belts and timing chains, as well as a blown head gasket and damaged valve train components can result in a loss of compression and lead to an engine misfire.
Sensor and Module Issues
Sensors provide the PCM with input that lets it operate devices like the ignition coils and fuel injectors. Once they fail, an engine misfire can occur.
Trouble Codes Associated with a Misfiring Engine
An engine misfire can cause the PCM to log several trouble codes. Some of these are:
- P0316 Code: Engine Misfire Detected on Startup (First 1000 Revolutions)
- P0307 Code: Cylinder 7 Misfire Detected
- P0308 Code: Cylinder 8 Misfire Detected
- P0313 Code: Misfire Detected with Low Fuel
- P0304 Code: Cylinder 4 Misfire Detected
- P0305 Code: Cylinder 5 Misfire Detected
- P0303 Code: Cylinder 3 Misfire Detected
- P0301 Code: Cylinder 1 Misfire Detected
- P0302 Code: Cylinder 2 Misfire Detected
- P0300 Code: Random or Multiple Cylinder Misfire Detected
- P0306 Code: Cylinder 6 Misfire Detected
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Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.
Black Smoke in the Exhaust
“A misfiring engine can also cause your vehicle to emit black smoke from the exhaust, which is a sign that the engine is not passing air and fuel correctly.”
What does not “passing” air and fuel mean? Does the air and fuel passing through the exhaust system, after it has left the cylinder, cause the misfire? How does that happen? Doesn’t the misfire occur inside the cylinder during the power stroke, before the fuel and air leave the cylinder?
Should that sentence state: “the engine is not burning
passingthe air and fuel correctly.”?Ignition System Problems
“An ignition misfire due to… …cause no burned air and fuel to be exhausted past the oxygen (O2) sensors, ‘leading to’ a misfire.”
Once again, un-burned fuel & air in the exhaust are the result of a misfire (either incomplete or no combustion) in the cylinder. The un-burned fuel passing the O2 sensor in the exhaust does not cause or “lead” to a misfire – that has already happened.
The sentence above doesn’t make sense. It’s the electrical/ignition problem, being discussed, that is causing the misfire. The O2 sensor has nothing to do with causing the misfire and it doesn’t need to be mentioned here. It’s irrelevant and confusing. Otherwise, it’s an interesting and informative article.