Are you hearing an odd sound when your car is running? Could there be a weird sound that comes from cylinder 4? If so, you are probably experiencing a cylinder 4 misfire.
The engine misfires when there is something wrong with the timing or the ignition components and you have to investigate the problem deeper. So, what you can do about it? We are going to cover everything in this article when it comes to the cylinder 4 misfire issue.
- What Is A Cylinder Misfire?
- Common Misfire Symptoms
- Diagnosing An Engine Misfire
- What Causes A Misfire?
- Costs To Fix A Misfire (& How To Fix)
- Final Conclusion
- Frequently Asked Questions (FAQs)
The engine is very complex and sometimes problems like this can appear. And they can also make us really annoyed because all of a sudden, the engine has decided not to work properly. And when something is wrong, this means that it has to get checked.
You just have to deal with these issues and think of them as something that you have to do. Only then, you are not going to be frustrated. Luckily, a misfire problem can be solved easily and pretty affordably. This depends on where you take your car to be serviced. Or, if you are one of those who can service the car by yourself. And we are going to cover all that.
In this article, we are going to discuss misfires. Why do they appear in the first place and what are the symptoms when your car’s cylinder 4 misfire occurs? Then, we are going to learn what are the common fixes and how you can diagnose a car that has misfired and fix it by yourself. We are also going to talk about the prices. So, let’s dive into it.
A cylinder 4 misfire is also known as error P0304, meaning that the PCM of the vehicle has detected some problems with this cylinder. These irregularities are alerting the powertrain control module (PCM), and the PCM is going to inform you with a check engine light that something is wrong inside the number 4 cylinder.
But you can never know that this cylinder is affected by the problem. This is mainly because the check engine light is only turned on. It doesn’t give you any more info on the situation and you have to connect the car to an OBD2 scanner tool to find out more (so long as you know how to use OBD2 scanner).
If you have the code P0304, you probably have a cylinder 4 misfire issue on your car. This is a clear indication that cylinder 4 is having some trouble running. Plus, this problem has to be addressed. You can address this issue in different ways and we are going to cover that later in the article.
But first, let’s discuss the main symptoms that happen you have an engine that misfires. Because the symptoms tell a lot even before the check engine light appears in the first place. In some cases, the check engine light does not appear at all. So, knowing the symptoms of a cylinder 4 misfire is key to solving this problem.
Cylinder Misfire Symptoms
When the engine is misfiring is developing some symptoms, it has to be noticed to identify the problem on time. If you understand these symptoms, you are going to be able to see when your engine is misfiring and very easily diagnose the problem. And what are the symptoms? That’s what we are going to cover in this chapter.
A cylinder 4 misfire can cause a variety of symptoms, from increased fuel consumption to difficulty starting the vehicle. It is essential to be aware of these symptoms and get your vehicle checked out if you notice any of them. Ignoring a cylinder misfire can lead to more severe and costly repairs in the future. It can also be dangerous, as it can lead to a loss of control of the vehicle.
If you experience any of the symptoms mentioned below, it is crucial to get your vehicle checked out by a professional as soon as possible. They will be able to diagnose the problem and recommend the necessary repairs to get your vehicle running smoothly again.
Cylinder 4 Misfire, Symptoms #1: Check Engine Light
As we said the check engine light is a clear indicator that something is really wrong with the engine. This doesn’t have to be always the case. But in most cases, when the check engine light appears, things are pretty serious.
That’s why you need to investigate the problem. You have to take your car to a mechanic to diagnose the issue. The car has to be connected to a computer and all the issues that your car has will be within a glance. That’s why having a scanner tool also always helps.
Even with the basic tools, you will have the information that you need. All you need is the error name or code for this problem. And in most cases, it’s the error P0304.
After you scan the car, you can type the name of the error on Google and find the solution right away. This will identify quickly that you have a cylinder 4 misfire. It’s that easy. That’s why you should never ignore the check engine light when it appears on your dash. Make sure that you diagnose the problem as soon as possible.
It is a good idea to get a scanner tool. They are relatively inexpensive and you will benefit from this investment in the long run.
Cylinder 4 Misfire, Symptoms #2: Engine Runs Rough And Shakes
If your engine runs rough at idle and shakes, then you probably have some ignition issues. This can be a problem because the engine cannot keep the momentum and starts to shake, as well as developing other issues as well.
Many different sensors can fail and cause this problem to appear. These include bad spark plugs (you can diagnose this by learning how to test spark plug and how to tell if spark plug is bad). One of the first things you have to do is to investigate the condition of your spark plugs.
You need to unbolt the spark plugs and see what is their condition. See if they are worn or if they have some other problem. Because spark plugs can tell you the story that is behind this. Replacing them will not always permanently solve your issue. And you will have to investigate the issue further that is causing the car to run rough.
Another reason behind this can be the coils. That’s if the ignition coils are bad. Then you have a problem with your engine. For this, you are going to need a scanner tool and you will have to scan the car for codes to find the real issue and see what’s causing a cylinder 4 misfire.
The code P0304 will give you some basic info. And it’s up to you how far you will go in troubleshooting the issue.
Cylinder 4 Misfire, Symptoms #3: Car Feels Underpowered
When there are no explosions in the cylinder, the car will also feel underpowered. When you are driving, you will probably think that the car just doesn’t feel right and there is something wrong with it. That’s because you don’t get the same input when you apply the gas pedal.
This is another indicator of a bad spark or a lack of spark in the cylinder. The fuel just doesn’t ignite as well as it used to. Resulting in low power from the engine.
If your car feels underpowered, then scanning the car for codes will be the next step that is going to tell you a lot about the issue. And if there is a cylinder 4 misfire or error P0304, you will have to take a step further and diagnose the issue. How you can do that is something we are going to cover in one of the next chapters.
Cylinder 4 Misfire, Symptoms #4: Exhaust Smells Like Unburnt Fuel
Another symptom when you are experiencing misfires in your car is the smell of gas coming from the exhaust. Let’s say your exhaust system produces blue smoke, and it smells like gas when you give it a smell test. In this case, you know that the fuel doesn’t ignite.
That’s why as we said the car has to be thoroughly checked on a computer to see what is causing the real problem.
Cylinder 4 Misfire, Symptoms #5: Car Jerks When The Driver Accelerates
If your car jerks when you apply the throttle can be an indicator of a cylinder 4 misfire as well. The engine just doesn’t work properly and your car doesn’t accelerate well. The car has trouble keeping the engine running.
This will be most noticeable on smaller displacement engines. Mostly, we can see 4-cylinder cars where the lack of work on one cylinder can be extremely noticeable and will affect your driving experience. That’s why if your car has trouble accelerating it can be caused by a misfire in one of the cylinders.
Cylinder 4 Misfire, Symptoms #6: Increased Fuel Consumption
These bad readings will fool the sensor that there is a lack of fuel inside the engine. When the PCM gets this bad data, it’s going to order the injectors to dump a lot of fuel inside the cylinders.
This increase in fuel dumped in the cylinder is going to result in a gas smell (for some context, check out our guide on how to get gas smell off hands) coming from the exhaust. As well as other problems like increased fuel consumption.
You will notice a significant drop in gas mileage when running a car with cylinder 4 misfire problems. That’s why this issue has to be diagnosed and see what is the real culprit. And that’s something that we are going to cover next.
Cylinder 4 Misfire, Symptoms #7: Engine Noise
Unusual engine noise is another symptom of a misfire. This noise is often described as a popping or banging sound. It happens because the fuel-air mixture in the cylinder is not igniting properly, which can cause the mixture to ignite at the wrong time or even not at all.
When the mixture ignites at the wrong time, it can cause a ‘knocking’ or ‘pinging’ sound. This is potentially very damaging to the engine and needs to be addressed immediately. If the mixture does not ignite at all, it can cause a ‘backfire’, which is a loud bang from the exhaust.
It is essential to get your car checked if you hear any unusual noises coming from the engine. Ignoring this problem can lead to more severe and costly repairs in the future.
Cylinder 4 Misfire, Symptoms #8: Poor Emissions
A cylinder misfire can also lead to poor emissions. When the fuel-air mixture in a cylinder does not ignite properly, it can lead to incomplete combustion. This means that not all the fuel is burned, leading to higher emissions of unburned hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx).
Increased emissions are not only bad for the environment, but they can also lead to your vehicle failing an emissions test. If you live in an area with strict emissions standards, this can be a significant problem.
Cylinder 4 Misfire, Symptoms #9: Difficulty Starting the Vehicle
A misfire can make it difficult to start your vehicle. This is because the engine relies on all cylinders firing properly to run smoothly. If one or more cylinders are not firing correctly, it can cause the engine to run unevenly, making it harder to start.
In some cases, the vehicle may not start at all. If you are experiencing difficulty starting your vehicle, it is essential to get it checked out as soon as possible.
Cylinder 4 Misfire, Symptoms #10: Engine Stalling
Engine stalling is another common symptom of a cylinder misfire. When a cylinder misfires, it can cause the engine to lose power momentarily. If this happens repeatedly, it can lead to the engine stalling.
Engine stalling can be particularly dangerous if it happens while you are driving, as it can lead to a loss of control of the vehicle. If you experience engine stalling, it is crucial to get your vehicle checked out immediately.
Cylinder 4 Misfire, Symptoms #11: Increased Vibrations
Increased vibrations are another symptom of a cylinder misfire. When a cylinder misfires, it can cause the engine to run unevenly, leading to increased vibrations. These vibrations can often be felt through the steering wheel or the vehicle’s floor.
While some vibrations are normal while driving, if you notice an increase in vibrations or if the vibrations suddenly become more intense, it is essential to get your vehicle checked out.
There are two ways to diagnose a misfire in an internal combustion engine. One of the ways is with experience. When a mechanic sees a car that misfires, they can tell right away that is misfiring. And if they listen to the motor, they can tell you which of the cylinders is misfiring. That’s why you need an experienced mechanic in your life that can tell you right away what is wrong with your car.
But, for inexperienced young mechanics, there are a lot of tools on the market that are going to help you out. There are basic OBD2 scanners that will give you the error code and you can take it from there. More precisely, when there is a cylinder 4 misfire, you are going to get an error code named P0304.
But if you look online for this code, you will only get assumptions about what can go wrong and the probable causes for it. For that, we are going to cover it next. These scanners are not going to tell you the precise reason why you are getting the code.
To understand the precise cause of a fault, you need an advanced scanner that knows all when you connect it to your car. These portable scanners are usually laptops that have factory software for some cars and they are going to tell you all you need to know.
The downside of this is that they cost a lot of money. And mostly, they are only sold to dealerships. Even though old ones can be bought online for a huge chunk of change.
That’s why you will have to troubleshoot the car. Or, take the car to a mechanic to tell you the problem right away. Then, replace the part. This is probably the best solution to your problem.
Cylinder Misfire Causes
If you want to troubleshoot and try to fix the problem on your own, you can try. That’s why we are going to give you a lot of hints about what could be your problem. This will come in handy because if you want to experiment and try to fix the problem by yourself, you are going to know which components you should look out for and replace. We are also going to give you some troubleshooting tips that will come in handy as well.
1. Bad Spark Plugs
If the spark plug is all black it means that there is a lot of carbon buildup on it. This, in other words, translates to the spark plug is bad. Also, the spark plug can be covered in gas and oil as well.
If there is gas on the spark plug then it means that your car is running rich. Or, if there is oil on the spark plug, it tells you that your valves or oil rings are leaking oil inside of the cylinder.
The best thing to do in this situation is to replace the spark plug with a new one and see if the problem goes away. If the problem disappears, then great. You are good to go. If not, then you need to check the other components like the coils, and we are going to cover that next.
2. Bad Ignition Coil
A bad coil can also cause your engine to misfire. The coil is an essential component that delivers the power to the spark plugs and has to work properly. If not, you will get misfires. When coils go bad, you usually also get error codes that are going to tell you which is the affected coil. But if you don’t get a code, you can troubleshoot the issue.
If you want to troubleshoot you can remove the coil from cylinder 4 misfire and replace the coil with a coil from another cylinder. If the cylinder stops misfiring then you have solved your problem. Simple troubleshooting has basically solved your issue.
In this case, you will have to get a new coil and replace the old coil with a new one. Then you are good to go. Otherwise, it’s handy to learn how to test ignition coil.
The downside is that the coils are not that cheap. A single coil can cost more than $100. That’s why replacing them can be difficult sometimes. That’s because not everyone has the funds to get a new coil or set of coils for their engine.
3. Bad Distributor And Wires
Bad distributors on older vehicles that are carbureted can also cause cylinder 4 misfire to appear. The distributor and wires are important components of every ignition system in older cars. If they are not properly working (or if you don’t know how to tune a carburetor), you are going to get a misfire and your engine will run poorly.
What happens is that the connections corrode and lose contact. This means that the spark plugs do not get the right amount of electricity to ignite the fuel and cause misfires. If your carbureted vehicle is misfiring, the first thing you should do is inspect the wires and distributor and replace them.
Replacing the wires and distributor is a simple task and almost anyone can do it. But the timing will require to be adjusted for the engine to work properly with the new set of wires.
4. Unadjusted Valves
Unadjusted valves can also cause your engine to misfire. That’s if your valves don’t open and close when they have to. In this case, you will start experiencing misfires. When the valves are not adjusted, they are basically sabotaging your engine.
To solve this problem, you need to get a valve adjuster tool and adjust the valves manually. Or, let someone else that has the experience to perform this work.
I’m saying this because valve adjusting is not something simple, it’s a science in itself. There are a lot of steps that make the adjusting of the valves perfect for every rotation.
That’s why taking your car to a mechanic for this type of job is the best way to go.
5. Faulty Fuel Injectors
Faulty fuel injectors can also cause the cylinder 4 misfire problem to appear. The injectors are the components that deliver the fuel to the cylinder. If an injector does not deliver the fuel accordingly the engine will start to misfire.
This can be the case when the injector is clogged up with debris and doesn’t allow the fuel to pass. In this case, you have only one option and that is to replace the injector.
Injectors for gasoline vehicles are pretty cheap and easy to come by. So, it will not be a big problem to replace one injector in your car. But if you have to replace a bunch of these it can add up.
6. Carbon Buildup
Carbon buildup also can be an issue when you have a misfire in your engine. This is a big problem for some engines that misfire daily. Since there are misfires, it means that the fuel does not burn all the way and creates a lot of carbon.
This carbon is starting to stick to the valves and the top of the piston. But what if the carbon buildup is very significant? In this case, it can clog the exhaust ports and make your valves unfunctional.
They will not seal properly and you will have a ton of issues running your engine. That’s why when there is a lot of carbon, it is a smart idea to clean off the heads. The exhaust ports have to be cleaned as well as the top of the pistons.
This job is also pricey since you will have to remove the head and clean it. It will cost you around $700 or less in some places to get this job done.
7. Vacuum Leaks
A vacuum leak can cause a cylinder misfire. The engine uses a vacuum to control several components, including the intake manifold. If there is a leak in the vacuum, it can lead to an uneven air-fuel mixture in the cylinders, causing one or more cylinders to misfire. Check all the vacuum hoses and connections for any signs of wear or damage. Also, a smoke test can help to identify any hidden leaks.
8. Poor Quality Fuel
Poor quality or contaminated fuel can lead to engine misfires. Water or other contaminants in the fuel can prevent proper combustion in the cylinders. Always buy fuel from reliable and well-maintained gas stations. If you suspect that the fuel is contaminated, you might need to drain the fuel tank and refill with fresh fuel.
9. Faulty Oxygen Sensor
The oxygen sensor monitors the level of oxygen in the exhaust gases and adjusts the air-fuel mixture accordingly. A faulty oxygen sensor can send incorrect data to the engine control module (ECM), causing an incorrect air-fuel mixture and, subsequently, a misfire. The oxygen sensor can be tested using a multimeter or an OBD-II scanner to determine if it is functioning correctly.
10. Bad Catalytic Converter
The catalytic converter is responsible for converting harmful exhaust gases into less harmful substances. If it is clogged or damaged, it can restrict the exhaust flow, leading to a loss of engine power and misfires. A noticeable decrease in fuel efficiency, a rotten egg smell from the exhaust, and a glowing red catalytic converter at night are signs of a bad catalytic converter.
11. Ignition Control Module Failure
The ignition control module (ICM) controls the ignition coil and spark timing. A faulty ICM can lead to irregular sparks and cylinder misfires. The ICM can be tested using a multimeter or an OBD-II scanner to determine if it is functioning correctly.
12. Engine Mechanical Problems
Mechanical problems within the engine can also cause a cylinder misfire. This includes a worn piston ring, a bent valve, a damaged cylinder head, or a blown head gasket. A compression test can help to identify any mechanical problems within the engine.
Engine Misfire Cost
The cost to fix the cylinder 4 misfires can be as simple as $5 for a single spark plug, or up to $700 for cleaning the heads from carbon.
Depending on the problem, the cost can vary widely. If you need new spark plugs, you will get the cheapest price. If you need coils and injectors you can expect to pay between $200 to $400. Or if you need valve adjustment you can also expect to pay $200 to $300.
If the carbon buildup is too thick, you will have to pay to remove the head and clean the valves, and adjust them. This can be the most expensive coming at a price of $700.
However, if you do want to learn how to fix a Cylinder 4 Misfire, here are some steps that you’ll need to go through:
Step #1: Identifying the Misfire
First, it is essential to confirm that a misfire is the issue. A misfire occurs when one or more of your vehicle’s cylinders fail to fire correctly. Common symptoms include rough idle, reduced fuel economy, and reduced power. An OBD-II scanner can help confirm a misfire by displaying codes like P0304, indicating a misfire in cylinder 4.
Step #2: Analyzing the Cause
Once you’ve confirmed the misfire, you need to determine its cause. Misfires can result from several issues, such as faulty spark plugs, defective fuel injectors, or a damaged ignition coil. Additionally, engine timing issues, low compression, or problems with the computerized engine control system can also lead to misfires.
Step #3: Checking the Spark Plugs
Spark plugs are a common cause of misfires. Remove the spark plugs and inspect them for wear, fouling, or damage. If they appear worn or damaged, replace them. If you’re unsure, it’s always best to replace them as they are relatively inexpensive.
Step #4: Inspecting the Ignition Coils
Ignition coils are responsible for converting the car’s low voltage to the thousands of volts needed to create an electric spark in the spark plugs. A faulty coil can lead to a misfire. Test the coil pack with a multimeter to ensure it’s functioning correctly.
Step #5: Evaluating the Fuel Injectors
Fuel injectors deliver fuel to the engine. A clogged or malfunctioning injector can cause a misfire. Use a stethoscope to listen for a clicking sound from the injectors, which indicates they are working. If you can’t hear a clicking sound, the injector may be clogged or damaged.
Step #6: Checking Compression
A compression test can help identify issues with the engine’s valves, head gasket, or piston rings. If the compression is low in the cylinder that is misfiring, this may be the cause of the problem.
Step #7: Assessing the Engine Control Module (ECM)
The ECM controls the ignition system, fuel injection, and other essential functions. An issue with the ECM can lead to misfires. Use an OBD-II scanner to check for any codes that might indicate an ECM issue.
Step #8: Repairing or Replacing the Faulty Parts
Once you have identified the faulty component causing the misfire, it’s time to repair or replace it. Depending on your level of mechanical skill, you may be able to do this yourself or need to take your vehicle to a professional.
Step #9: Reassessing the Vehicle
After the repair or replacement is complete, clear any trouble codes from the ECM with an OBD-II scanner. Then, start the vehicle and let it run to see if the misfire persists. Take the car for a test drive to ensure the problem is resolved.
Step #10: Regular Maintenance
Preventive maintenance can help avoid misfires. Regularly change your oil, replace air and fuel filters, and keep an eye on the fuel system and ignition components.
Remember, while a cylinder 4 misfire (P0304) is specific to that cylinder, the steps for diagnosing and fixing the misfire are the same for any cylinder. Additionally, if you are uncomfortable performing any of these tasks yourself, it is always advisable to seek help from a professional.
Code P0304: Facts You Need to Know
- Code P0304 means “Cylinder 4 Misfire Detected” and indicates that cylinder 4 is experiencing misfires.
- This issue is severe, and driving with this error code should be avoided to prevent serious engine damage and dangerous driving conditions.
- The causes of cylinder 4 misfires can range from a faulty ignition system, fuel system, or internal engine failure, but the most common reason is faulty or worn-out spark plug coil packs.
- Symptoms of code P0304 include a check engine light flashing or on, engine roughness or shaking, lack of engine power, fuel smell from the exhaust, hesitations/jerking when accelerating, and commonly associated with error code P0300.
- To fix code P0304, the first step is to get it diagnosed by finding a trustworthy shop to pinpoint the problem quickly and accurately.
- Diagnosis may require an hour of “diag time” costing between $75-$150 depending on the shop’s labor rate, and the cost of repairs will depend on the underlying issue, which may require replacing spark plugs, ignition coils, spark plug wires, fuel injectors, vacuum leaks, fuel pumps, or fuel pressure regulators.
- DIY diagnosis is possible but recommended for intermediate-level repairers who have specialized equipment beyond what the FIXD Sensor can provide.
- Diagnosis steps involve using FIXD to scan the vehicle, checking for loose connectors and damaged wiring, checking the condition of spark plugs and spark plug wires, testing the fuel system, and performing an engine compression and leakdown test if necessary.
- Common diagnosis mistakes include overlooking loose-fitting electrical connectors and broken or disconnected vacuum hoses.
Cylinder 4 Misfire: In Conclusion…
In this article, we have covered a lot when it comes to cars that misfire. That’s especially the cylinder 4 misfire problem. This problem can be a headache for many car owners and they can have a hard time fixing this issue.
But you shouldn’t worry, we have covered the ways how you can diagnose this issue. Also, as to what are the main symptoms when you have a cylinder 4 misfire?
And lastly, we covered some of the culprits that can cause the engine to misfire. These were the spark plugs, the coils, wires and distributor, injectors, and unadjusted valves.
FAQs On Cylinder 4 Misfire
If you’re still curious to learn more about a cylinder 4 misfire, our FAQs here might help…
How To Fix Engine Misfire
To try and fix a misfire, you’ll first have to determine what caused it to occur, in the first place. This can be done by a thorough diagnosis using an OBD2 scanner, which at least gives you a starting point of what might’ve prompted a misfire to happen. Then, you can go down the rabbit hole one by one. Start by checking the spark plugs and ignition coils, before moving on to checking for vacuum leaks, looking at the fuel pressure, and measuring your engine’s compression. Once you know what particular component’s failed, a repair or replacement of said component should be in order. For example, if the misfire is caused by bad spark plugs, consider replacing them and see if it fixes it.
What Is A Misfire
In engine terms, a misfire is basically incomplete combustion within a cylinder. The name stems from the fact that a particular cylinder (or in some instances, more than one cylinder) fails to fire, ignite, or combust. This is when the combustion reaction in one (or more) cylinders fails to happen, and thus it fails to ignite the mixture of fuel and air inside that cylinder. When that happens, your engine will stumble, stutter, and you’ll see how the engine speed (i.e. your RPMs) momentarily drops, as one of your cylinders failed to fire. Misfires can occur regardless of your engine’s status, such as whether you’ve just started your car, or while you’re traveling at high speeds.
What Can Cause A Misfire
Misfires are among the most tedious car-related issue to diagnose and pin down, as they can be caused by a myriad of potential points of failure. Most commonly, cylinder misfires are caused by worn-out spark plugs, which aren’t able to reliably and properly ignite the air-and-fuel mixture within a cylinder. Similarly, a faulty ignition coil would not be able to sufficiently supply enough power to the spark plugs, causing a chain reaction. The same goes for bad spark plug wires and malfunctioning distributors. A carbon build-up within the engine would further inhibit its ability to properly ignite the fuel-and-air mixture, as well as clogged fuel injectors that won’t allow fuel to pass.
Can You Drive With A Misfire
Technically speaking, you could still drive your car, even if the engine is misfiring. Should only one cylinder misfire, you’ll no doubt notice a steep loss of power and poor driveability. Yet, you can still move it around safely, so use that opportunity to head over to the nearest possible workshop to have it looked into and fixed ASAP. Otherwise, it’s a bad idea to drive a car for lengthy periods of time and go long distances when the engine is misfiring. This is because a misfire is typically a symptom of a greater or more serious underlying issue somewhere in the engine. If you don’t have it fixed now, it might fester and cause even larger (and costlier) problems down the line.
How To Tell Which Cylinder Is Misfiring
Usually, when an engine misfire happens, it only affects one cylinder (rarely, does more than one cylinder misfire at a time). So, how can you tell which particular cylinder is misfiring, and which ones are fine? Well, the easiest way to tell is by plugging in an OBD2 diagnostics scanner into your car and scanning it for any error codes. Should the OBD2 scanner display any error code between P0301 to P0312, then you’ll know which cylinder is misfiring – with the last 2 digits telling you the cylinder number. So, if the scanner shows P0303, then cylinder 3 is misfiring, while P0308 shows that cylinder 8 is misfiring, and so on from cylinder 1 all the way to cylinder 12.