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Cylinder 4 Misfire Detected: Causes, Symptoms, and Everything You Need to Know!

Cylinder 4 Misfire Detected: Causes, Symptoms, and Everything You Need to Know!

The power unit of your engine is its cylinder. If your cylinder gets faulty and doesn't fire properly, it could lead to a much bigger problem. You will know if it starts to go bad when you see the Cylinder 4 Misfire Detected or the P0304 OBD2 code which is also an early warning sign of an engine misfire. What causes it and what are the symptoms? Let’s find out!

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Cylinder 4 Misfire: What do cylinders mean in an engine?


Before we get to answer the hows and the whys of a cylinder 4 misfire, we need to understand the cylinders first. 


A typical car engine usually has 4, 6, or 8 cylinders. The cylinders provide power to the engine since it is where the fuel is burned and converted into mechanical energy. 


The cylinders have pistons that move up and down. They compress the fuel, igniting it that leads to combustion. The more cylinders an engine has, the more pistons there are that combust the fuel. This means that more power will be generated. 


Car engines have different types of cylinder layouts. The efficiency factor of a vehicle can be determined by the type of cylinder layout its engine has. The different types of cylinder layouts include inline, straight, flat, and V. Straight or inline engines usually have less than six cylinders, the flat layout has four to six cylinders, and the two-rows like the V engine that has a “V” formation has more than six cylinders. 


A cylinder that is not working properly or efficiently can cause leaking, overheating, or misfiring.  


Cylinder 4 Misfire: What does misfire on cylinder 4 mean?


One of the symptoms of a faulty cylinder is misfiring. If you suddenly see the trouble code P0304 or the cylinder 4 misfire detected, it means that cylinder 4 is not firing properly. This happens when your vehicle’s Engine Control Unit or the ECU detects that there is something wrong with it. 


The ECU is known as the brain of the engine. It controls all the functioning of the engine including monitoring the operation of all the cylinders by ensuring that the cylinders are firing on time. If one cylinder fails to fire again and again, the ECU will set off the check engine light with the trouble code P0304 or cylinder 4 misfire detected. 


Cylinder 4 Misfire: What causes a cylinder misfire?


A cylinder misfire happens when there is an insufficient amount of fuel burning in the cylinder. It occurs because a vehicle needs to burn the right amount of fuel and it has to burn it efficiently in order for the engine to operate properly. This is because fuel combustion plays an important role in the overall operation of the engine. It is its primary source of power.  The absence or incomplete combustion in an engine cylinder can cause it to misfire. 


Your vehicle’s engine has a lot of components that can trigger a misfire but with the trouble code P0304 or cylinder 4 misfire, you can narrow down the possible causes and cross out the other components since the code is specific for cylinder number 4. 


Other causes of a cylinder 4 misfire include:


  • Faulty spark or ignition system. 


Check the spark or ignition system of your vehicle. Inspect and look for any signs of heat damage and wear and tear of all its components. Cylinder 4 misfire can be caused by a faulty or worn spark plug and faulty spark plug wires or coils. Spark plug terminals should maintain a sandy color but if it has blackened with soot, it means the combustion chamber is overheating.  A spark plug terminal with a greenish color means that there might be a problem with the coolant. 


Problems with the ignition coils and cables can be causing the cylinder 4 misfire, too. Inspect the ignition system and check if the firing voltages are firing evenly. It should be at 8V to 10V per cylinder.

  • Issues with the fuel delivery system.


It has already been established that an inappropriate amount of fuel burning in the cylinder can trigger a misfire. Fuel delivery issues can be caused by a faulty injector circuit or a damaged fuel injector.

  • An exhaust gas recirculation malfunction.


This is something that doesn’t usually lead to a cylinder 4 misfire but an uncommanded Exhaust Gas Recirculation or EGR flow can still cause it. A leaking EGR or restricted ports can trigger it. 

  • Vacuum leaks.


A vacuum leak that is only confined to cylinder 4 or to any cylinder can cause a cylinder misfire. This happens because a vacuum leak enables additional air to get to the affected cylinder. This dilutes the air to fuel mixture. 


Under normal circumstances, all the engine’s cylinders should be getting the same air to fuel mixture so they can produce the same amount of horsepower and torque. If the mixture gets too diluted, it becomes too lean that the spark plug will have difficulty igniting it which results in a misfire. 

  • A mechanical engine failure.


Issues in your mechanical engine can also result in a cylinder 4 misfire. It could be caused by blown head gaskets, weak piston rings or valve train issues.   


Cylinder 4 Misfire: How do you diagnose a P0304 trouble code?


To enable combustion on any cylinder, your engine needs to have air, fuel, and a properly timed spark. Without any of these three factors, it will surely result in a misfire. If you see the trouble code P0304 or cylinder 4 misfire detected, there must be some missing factors from the combustion process and you must find out what it is. 


To diagnose the trouble code P0304 you need to prepare some tools like an OBD2 scan tool, fuel pressure gauge, digital multimeter, compression tester, and a leakdown tester. Follow these steps to determine what causes the trouble code to set off. 


  1. Scan your system using an OBD2 scan tool. You need to check your system for any additional trouble codes. If it turns out that your system has other existing codes other than the codes P0300 to P0308, you need to correct them first to avoid misdiagnosis and you can cross out any other possible problems. 


  1. Conduct a visual inspection of all the wirings and connectors associated with your fuel or ignition system. Look for damaged wires and loose connections. 


  1. If you can’t see any visual signs or damages, swap cylinder number 4 coil packs with the packs in cylinder 1 if your engine has individual coil packs. When the swapping is done, proceed to clear the codes, start your engine, and test drive your vehicle. If you notice that the misfire jumps to cylinder 1, then it means that the coil pack is faulty and it needs to be replaced.


  1. If the misfire issue does not jump to the other cylinder, you can also repeat the swapping process but this time, swap the corresponding spark plug wire and spark plug. If switching these components results in a shift in the affected cylinder, then you must replace it. 


  1. You can also visually inspect your spark plug and inspect it for carbon build-ups or for any signs of fouling. If it has build-ups or is fouling, remove it and clean it thoroughly. If the build-ups can’t be cleaned or removed, it needs to be replaced. 


  1. Measure the resistance of your spark plug by using a digital multimeter. If the reading goes higher than 15,000 ohms, you will need to replace the wires. 


  1. Next is the ignition coil. To begin, you need to remove the coil. Use a multimeter and check it by touching the multimeter leads on the primary and secondary ignition circuits. If the reading shows 0, it means that you have an internal short. You can refer to your owner’s manual for your unit’s exact specifications but it usually has readings of .4 to 2 ohms for the primary ignition circuit and 6,000 to 10,000 ohms for the secondary circuit.


  1. Another thing to check for a detected cylinder 4 misfire is the proper fuel delivery. You can check it by attaching a gauge on your engine’s fuel rail schrader port. Take note of the reading and compare it to your vehicle’s manufacturer specifications. 


A faulty fuel pump, failed fuel pressure regulator, or clogged fuel filter can be the culprit of the trouble code if it is confirmed that there is low fuel pressure. 


  1. Unplug the fuel injector from your engine. Using a multimeter, probe its terminals and compare the resistance reading to your manufacturer’s specifications. If there is an obvious difference, you might have a faulty fuel injector. 


  1. If you fail to find the source of your engine’s malfunction, doing an engine compression test and a leak-down test will be necessary. Issues on its mechanical components can trigger a cylinder 4 misfire and these tests can identify which of the components is faulty.   


Cylinder 4 Misfire: How do you fix a cylinder 4 misfire?


Symptoms of a cylinder 4 misfire might include check engine light on, lacking or losing power, hard starting, poor performance, strange-smelling emissions, and shaking when the engine is on. If you have a cylinder 4 misfire detected or a P0304 code but you are not experiencing any symptom, you can clear the trouble code and do a test drive.


If the trouble code was set off again after clearing it, follow the steps below to help you fix the problem.


  • Fix the other existing codes. The cause of the triggered P0304 trouble code might be uncovered as you fix the other trouble codes. 
  • Remove and replace any damaged wires you found while inspecting your system. Replace other malfunctioning components too. 
  • Check your vehicle’s Exhaust Gas Recirculation or EGR system and fuel injectors for clogs and clean them if you find any.
  • Inspect and test your fuel and exhaust system’s sensors. This includes your camshaft sensor, crankshaft sensor, mass airflow sensor, and oxygen sensors. If damage has been found in any of these sensors, have them replaced.
  • Inspect, remove, and replace any components of the fuel system that causes insufficient fuel pressure. You need to replace faulty fuel filters, too. 
  • If a cylinder 4 misfire is a result of low compression, then an internal mechanical repair of your engine is needed.  


Additional Tips.


Little preventative measures can go a long way in preventing cylinder misfires. You can check all the hoses in your system for leaks regularly. This is because misfires are usually caused by air-to-fuel mixture issues. 


Using the wrong fuel can also trigger misfires. It is better that you stick to a fuel that has the grade recommended for your engine.

Cylinder 4 Misfire: How serious is a cylinder 4 misfire?


Remember that a misfiring cylinder is a serious problem. Although a cylinder 4 misfire still enables you to drive to a safe location, it is recommended that you have it fixed as soon as possible. It is better that you drive immediately to your local repair shop once the symptoms start to show. This is because there are many potential drivability problems connected to the P0304 trouble code. 


A misfiring cylinder can lead to a number of problems if it is not addressed immediately. If you choose to ignore it, it can cause serious and irreversible damage to your engine and your catalytic converter. You don’t want that to happen since these parts are two of the most expensive parts to replace. 


Driving a vehicle with a misfiring cylinder can compromise your safety. It is very dangerous to drive a vehicle that is not firing on all cylinders. This is because when you are driving and your cylinder suddenly goes out, it can cause an accident that not only harms you but can also harm the people around you including other drivers and pedestrians.


Cylinder 4 Misfire: Final Word


Bear in mind that the experts advise that you need to have your vehicle checked the moment it shows a P0304 trouble code or cylinder 4 misfire detected. With our guide outlined above, you can check and fix the issue yourself. Make sure that you study it first and follow the process. If you find yourself struggling to fix it yourself, don’t hesitate to ask for help and call the professionals.