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How To Fix P0304 Code: A Comprehensive Guide!

How To Fix P0304 Code: A Comprehensive Guide!

If you notice your car is experiencing problems such as rough idling, hesitation, lack of power, or is consuming more fuel than usual, you might need to check for any stored trouble code in your system. If you find a P0304 code, then it means that cylinder number four is not firing as it should. When you see the P0304 code or “Cylinder 4 Misfire Detected” in your system, it needs to be fixed immediately since engine misfires can lead to serious damage to your engine. If you wonder “how to fix P0304 code”, the solution can vary depending on what caused the problem. But usually, how to fix P0304 code involves replacing the cap and rotor, plug wires, coil pack, or spark plugs, as well as fixing fuel delivery issues or any air leaks.

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The P0304 trouble code should never be ignored since it can negatively affect your driving experience. It is best to correct the problem immediately. If you want to know more, continue reading! With this comprehensive guide, we will discuss everything you need to know!


How to fix P0304 Code

How to Fix P0304 Code: What Would Cause a P0304 Code?



Before we discuss the ways on how to fix P0304 code, let us understand what is this code and what causes it. The P0304 trouble code stands for “Cylinder 4 Misfire Detected.” This means that the car’s onboard computer has detected or counted enough misfire occurrences on cylinder number 4 to store the misfire code for the said cylinder. Cylinder number four is the fourth cylinder as they were numbered.


The trouble code P0304 means that the cylinder number four is having misfires, but what is a cylinder? The cylinder is one of the engine components that creates power. It is an important engine component since it is a chamber where the fuel is combusted, which produces power. The motion of the cylinders, when the spark explodes the air and fuel mixture, turns the crankshaft which will then turn the car’s wheels.


This process is what is referred to as the cylinder firing. When the cylinder misfires or is not firing as it should, it can be caused by a number of issues. When this happens, you might see the code P0304 that leads you to wonder, “ how to fix P0304 code.” A misfire can happen when there is an improper amount of fuel burning in a cylinder. You need to remember that a right amount of fuel burning in a cylinder is vital to the overall operation of the engine since the fuel combustion is what supplies the energy needed to power the car’s engine.


When you spot a P0304 trouble code, it is the car’s onboard computer alerting you that one of your cylinders is misfiring but it does not tell you what caused it or why it happened. You need to find out what caused it so you can have it fixed immediately since failing to do so can lead to major damage to your engine. So what causes the code P0304 to be stored in your system? The trouble code P0304 can be caused by any of the following issues:


  • Problems with the ignition system which include a worn or damaged spark plug, a faulty coil pack or coil-on-plug coil, or a faulty spark plug wire equipped on a car that has plug wires.


  • Problems with the fuel delivery which include a bad fuel injector, issues with the engine control unit or powertrain control module like a damaged injector driver, or wiring problems with the fuel injector circuit such as damaged wires or loose connections.


  • The engine has some mechanical problems which include a worn or faulty piston ring, a faulty piston or damaged cylinder walls, a leaking valve, a faulty or worn camshaft lobe or damaged lifter, or a leaking head gasket.


  • Other problems such as a failing distributor, defective distributor caps, a vacuum leak, faulty camshaft or crankshaft sensors, off engine timing, engine compression is low, fuel with low quality has been used, low fuel pressure, defective O2 sensor, faulty mass airflow sensor, faulty throttle position sensor, a defective car onboard computer, or a faulty EGR system.


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How to Fix P0304 Code: Can I Drive With a P0304 Code?

When you ask how to fix P0304 code and you find out how it’s done, you need to make sure that you will be doing it immediately. Don’t try to drive your car with a misfiring engine. If you ask, “can I drive with a P0304 code?” The answer is no, you can’t. It can compromise your safety and it can lead to severe damages to your engine. You don’t want to deal with a very expensive repair bill or ask the question, “replace my engine or buy a new car?


When you see the trouble code P0304 stored in your system, you should find out what caused it and have it corrected immediately since it is usually considered as a serious problem. This is because any problems that are related to spark or misfires can result in unburnt fuel to enter into your car’s exhaust, which will then be extremely heated. When this happens, it can cause problems to your catalytic converter, which can lead to premature damage or failure.


It is best to find what caused the P0304 trouble code to show up in your system and have it fixed right away. This can help prevent unnecessary problems which can lead to a very costly repair bill. You can diagnose or fix the problem yourself, which we will discuss later on as well as the procedures on how to fix P0304 code. However, if you are not that confident or comfortable in doing the repair yourself, you can just take your car to an auto repair shop and have a professional handle the diagnosis and repairs for you.


You will know if your have a problem with a misfiring cylinder or a trouble code P0304 when you experience any of the following symptoms:


  • An illuminating check engine light.
  • Flashing check engine light.
  • It is hard to start your car’s engine.
  • The engine is running rough and is shaking.
  • Rough idling.
  • Lack of engine power, especially when you are driving uphill.
  • Your car is consuming more fuel than usual.
  • Hesitations or jerking when you are accelerating.
  • You notice foul odor coming from your car’s exhaust.


How to fix P0304 Code

How to Fix P0304 Code: How Do I Fix the Engine Code P0304?



How to fix P0304 code can be done in a number of ways, usually by just repairing or replacing the component that caused the misfires. The procedures on how to fix P0304 code can vary from car to car, but in general, it can be done by following the simple steps listed below.


  • Consult the owner’s manual of your car.


Before you perform any type of do-it-yourself repairs or disassembling a car component, you need to consult your owner’s manual first and look for any specific instructions or important details about it that you need to know.


You need to familiarize yourself with the specific details or instructions as well as the locations of the components that you need to check. You should also know the proper torques or the proper ways to remove or install the car’s components.


  • Look for any other diagnostic trouble codes stored in the system.


You need to look for any other diagnostic trouble codes stored in the system before starting the diagnostic process and the procedures on how to fix P0304 code. By using a diagnostic scanning tool, look into your system and find out if there are any additional trouble codes stored. By doing so, you will be able to correct the said problem as well. It can also give you an idea what the problem really is.


  • Inspect the freeze-frame data.


When diagnosing the problem that caused the P0304 trouble code, you can also inspect or assess any freeze-frame data that has been recorded during the logging of the said trouble code. This is done since the said data can provide additional details or information which can be used in the diagnostic process. You can use the information such as the specific RPM range where the recorded cylinder misfires occurred.


  • Check all the ignition system components thoroughly.


You should thoroughly check all of the components of your ignition system, looking for any signs of damage or failure. This is done because most misfires happen when one or more components of the engine’s ignition system start to become faulty or bad. You should thoroughly inspect components such as the spark plugs. Spark plug wires, distributor cap of the engine, and rotor button, if your car is equipped with one.


If your car has individual coil packs and not spark plug wires, you can remove the cylinder 4 coil and swap it with the cylinder 1 coil. If the problem moved to cylinder 1 or your system stores a P0301 code, then it means that you have a faulty coil pack and will have to be replaced.


You can do the same thing with the spark plug, swapping and moving the cylinder 4 plug to another cylinder. If the problem moved to the that cylinder, then the plug is faulty and needs to be replaced. Once the faulty component has been replaced, check your engine again for misfires.


  • Check if there is a spark.


If you did not find any signs of damage on your engine’s ignition system components, the next thing you need to do is to determine whether there is a spark on the affected cylinder or not. This step on how to fix P0304 code can be done by using an inline spark tester. If after testing you find out that there is a lack of spark, it is an indication that there is a problem somewhere and you need to do some further investigation on your ignition system.

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  • Check the integrity of your car’s fuel system.


The next thing you need to do is to check the integrity of your car’s fuel system and make sure that it is operating properly and efficiently. You can check it by using a fuel pressure gauge connected into the fuel rail of your engine. You should get a “key on” fuel pressure readings or a reading which is more than what is specified by your car manufacturer.


You can also use a bi-directional scan tool since it can be helpful in checking or assessing your engine’s injectors. This type of scan tool enables each of your engine’s injectors to be fired and release a small amount of fuel into your combustion chamber. When this happens, you may notice a quick dip in your fuel pressure.


  • Do a compression test.


If after doing inspections and tests you found no problems with your car’s fuel system, the next step on how to fix P0304 code is doing a compression test on the affected cylinder. When you perform a compression test, you should compare the compressions readings from the rest of the cylinders of the engine.


You can also do a leak down test if you want to be sure. Any inconsistencies found during the leak down test can be an indication that there are some internal mechanical problems that need to be addressed as soon as possible. The mechanical problems include a broken valve spring, leaking head gasket, worn valve guides, broken piston ring, burned valve, and faulty timing chain.



How to fix P0304 code can be done by repairing or replacing the faulty component that caused the misfire. You can follow the procedures listed above, but you need to make sure that you are comfortable doing the tests and repairs yourself. If not, you can take your car to an auto repair shop and have a mechanic do the needed repairs . Depending on what caused the problem, the repair might cost you somewhere between $50 and $2,000. If the repair needed turns out to be very expensive, you can assess your car’s condition and market value. You should determine whether it is worth it to have your car repaired or just sell your damaged car as is.

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