A car misfire or engine misfire is a sensation you will instantly recognize but just as quickly forget about. Your engine will stumble for a brief moment and then regain its pace again. However, just as soon as the rpm settles down, your car misfire appears again.
“Something is wrong,” you will tell yourself, and the daunting feeling of automotive problems hide behind your shadow of wisdom for your car's mechanics. Then there is the sinking feeling attached to the possible repair expenses.
Several faults can cause car misfires, but some suspect causes occur more frequently than others. If you are sitting behind the steering wheel of a car with engine misfires and wondering what to do, then continue reading to learn more about the problem and what you can do about it.
What is a Car Misfire?
A misfire results from incomplete or zero combustion inside one or more of your engine's cylinders. To you, as the driver of the car with a misfire, it will feel as though there is hesitant shaking when your vehicle is running. Misfires are one of the most common problems experienced by cars with a modern gas engine.
To better understand a car misfire concept, it is best to understand the basics of a car's engine first. A car's pistons and crankshaft move inside the engine's cylinders when it is running. An explosion inside the cylinder is what pushes the pistons down.
When the piston is pushed down, the crankshaft is spinning inside the cylinder. A four-cylinder engine works in the following four steps and repeats this cycle after the fourth step:
- When the piston goes down, it causes the cylinder to fill with an air-fuel mixture from the intake.
- When the piston rises, the air-fuel mixture is compressed to high pressure.
- The ignition from the spark plug ignites the air-fuel mixture, and the explosion pushes down the spinning crankshaft.
- The piston goes up, and the burned air-fuel mixture is emptied through the exhaust pipe.
A four-cylinder engine is found in most modern car engines and follows the above process repeatedly when running. A misfire occurs when one or more of the above stages is missing or not functioning correctly.
A misfire occurs when the fuel, oxygen, or spark of a car are not working in the correct order or at the right time. This will have a significant impact on your vehicle's overall performance; however, it doesn't mean that your car will stop working. If just one cylinder is the culprit of the misfire, then the rest of your cylinders will continue to function normally.
If a car misfires, you will have an increase in your emissions and reduced fuel efficiency. You will also notice that the engine jerks a lot. So, while you can still drive a car with an engine misfire, it is not recommended since an engine misfire can ruin your engine. It should be fixed as soon as possible.
Symptoms of a Car Misfire
Several faults can cause a misfire, which makes it challenging to troubleshoot if you do not know what signs and symptoms to look for.
Below is a list of the most common symptoms associated with a car misfire:
- Rough Idle
Sometimes, your engine will misfire when you are idling because your engine sensors will receive faulty values, and your air-fuel mixture will no longer be stable. This will result in an uneven idle that can be felt; you will feel your car jump up and down. Your engine may also shut off when idling.
- Rough Acceleration
When a misfire happens, you may feel a strong jerk coming from your car's engine. Often, a misfire will come under load from the engine, especially when you accelerate hard.
The most common occurrence when you will notice your engine misfire is on high gears, when you floor the accelerator, and on low RPMs. Rough acceleration is a common indication that your engine is misfiring.
- Slow Acceleration
A misfire can cause the oxygen sensors to receive faulty information. This will result in a mixture that is too lean or too rich. An unbalanced mixture can result in decreased acceleration and may put your car into limp mode. If your vehicle enters limp mode, it can cause your engine not to rev higher than 3500 RPM's and shut off the boost pressure from the vehicle's turbocharger.
- Check Engine Light
No one wants their check engine light to come on because it is a definite indication that something is wrong. However, it can alert you early enough to avoid severe damage that can occur when a problem is left unattended.
Modern cars have a variety of sensors on the engine. If one of these sensors fails or picks up a problem with your engine, it will send the information to the engine control unit. When the engine control unit receives this information, it will determine if the problem is serious or not. A recurring problem or severe issue will light up your check engine light.
In an engine misfire event, it is common that the engine light will come on, and a trouble code on the cylinder will be stored. This code can be checked with a diagnostic scanner.
In order to get as few vibrations as possible, a car's engine is well-balanced when manufactured, a process that often balances the axles. When one or more of the engine's cylinders do not fire correctly, then an imbalance occurs that causes heavy vibrations inside your cabin on idle and acceleration.
- Engine Sound Changed
Different engines carry different sounds. For instance, a V8 engine will sound very different from a 4-cylinder engine. You will know the sound of your own engine well enough to know when it doesn't sound right. If your 4-cylinder engine has a misfiring cylinder, it will sound like a three-cylinder engine.
What Does a Car Misfire Feel Like?
You will be able to feel your car has a misfire because the engine will feel as though it is stumbling for a few seconds before it regains its pace again. The number of times you feel the drop in performance or the jerking sensation will depend on the severity of the car's misfire.
When you step on the gas pedal, you may feel as though it takes a long time for your car to go faster, and you may even notice a cloud of smoke behind you. This is a symptom of an engine misfire.
What Does a Car Misfire Sound Like?
Think of popcorn kernels randomly popping. That sound is the best way to describe the noise an engine cylinder misfire makes.
In some cars, it could sound like a sneeze or “chug.” Technically, a backfire is different from a misfire. However, a loud “bang” or “poot” sound can be heard from both instances.
What Causes a Car Misfire?
As we have previously mentioned, several causes can contribute to a car misfire problem, but some causes occur more frequently than others.
Some common causes of a misfire include the following:
- Bad Ignition Coil in New Cars
- Bad Spark Plugs
- Bad Distributor in Old Cars
- Intake Manifold Gasket Leaks
- Faulty Fuel Injector
- Low Fuel Pressure
- Air to Fuel Ratio Imbalance
- Low Compression
- Control Circuit Problems
Let's take a look at some of these causes in closer detail.
Bad Ignition Coil / Distributor
The most common cause of a car misfire is the ignition coil. Some vehicles have a separate ignition coil on each one of their spark plugs, and others have just one coil with a sparking cable that connects each spark plug.
Older cars may have an ignition coil, but most older cars have a distributor. If you have separated spark plugs, you can unplug each coil to determine if any of the cylinders are not responding.
If you do find a faulty ignition coil or a trouble code stored on one, then replace it as soon as it is found.
Bad Spark Plug
With the ignition coil being the most common cause of a car misfire, the second most cause is bad spark plugs. Spark plugs fire up your engine's cylinders, and just like other components in your car, they wear out over time. Luckily spark plugs are generally a cheap purchase and pretty easy to replace.
If you cannot recall the last time you replaced your spark plugs in your car, then it may be time to replace them with new ones.
Intake Manifold Gasket Leaks
Intake manifold gasket leaks near the engine's cylinder heads are also a common problem with spark plugs. However, this problem occurs more frequently in older cars that do not have a steel gasket for the intake.
If you do have an older car, then you should check for an intake manifold gasket leak. If you own a newer, more modern vehicle, then it may be worth checking for any signs of a leak around the intake manifold gasket; in particular, look for any broken vacuum hoses.
Faulty Fuel Injector
This problem was more common about five years ago, but a faulty fuel injector can still cause a car to misfire, even in newer cars. Unfortunately, this is a difficult problem to diagnose without flow testing the fuel injector.
Since this cause is more prevalent in older vehicles, you may want to check out the other possible causes first if you own a newer car, but it is still worth checking to eliminate the fuel injector as being problematic.
Low Fuel Pressure
Low fuel pressure can be caused by:
- A faulty fuel pressure regulator
- A defective fuel pump
- Or a clogged fuel filter
Low fuel pressure can result in a lean mixture in your engine, which causes misfires on all the engine's cylinders.
If you have trouble codes for misfires on your cylinders, then you will want to investigate your fuel pressure and the fuel pressure regulator.
Air-to-Fuel Ratio Imbalance
Another common cause of a car misfiring can be attributed to an air-to-fuel ratio imbalance within the internal combustion chamber. This means that there is not enough fuel and too much air that is being mixed together.
For the combustion to be successful in your engine, the mixture needs to have more fuel than air; otherwise, you may notice a misfire when your engine idles. However, when you accelerate faster, the symptoms of your car's misfire will go away.
An air-to-fuel ratio imbalance can occur as a result of:
- A bad fuel pump
- A bad airflow sensor
- Or a clogged fuel filter
If you have checked all of the above causes and still cannot find out why your car has a misfire, then there could be a risk that your engine has low compression.
A faulty timing belt adjustment can cause low compression, which results in an engine misfire. If you have recently changed your timing belt, then ensure it was installed correctly.
Other causes of low compression include:
- Worn or Damaged Piston Rings
- Worn or Damaged Pistons
- Faulty Valve or Valve Seals
- Wrong Camshaft Timing
- Cleaned Cylinder Walls
- Cracked or Damaged Cylinder Walls
- Worn or Damaged Head Gasket
- Faulty Hydraulic Lifter
Control Circuit Problems
All of the input and output engine management devices, including the sensors and ignition coil packs, are connected with electrical circuits where necessary. Problems can occur within these circuits, such as a loose connection or damaged wiring that can cause a car misfire.
The Cost to Repair a Car Misfire
The repair costs on an engine that is misfiring are going to depend on the cause of the misfire. A few dollars can replace a faulty spark plug (if that is the problem), or you may need to pay a couple of hundred dollars if you need to replace your fuel injection system. On average, you could pay between $300 to over $1,000 for your misfire repair.
If you find that the repair costs related to the cause are beyond your financial means, it sometimes works out better to junk your vehicle and replace it with a new one. Using a junk car removal service like Cash Cars Buyer will help you put money back in your pocket as you sell your damaged vehicle as is to them and move onto something more efficient and reliable.