What are the causes of the P0304 misfire fault code?
3 Answers
After the P0304 misfire fault code appears, the engine's fuel supply system, ignition system, intake system, and cylinder pressure should be checked. If the cylinder pressure is too low, a phenomenon of cylinder pressure loss will occur, leading to engine misfire. Detailed explanations about engine misfire are as follows: 1. Engine misfire is determined by the crankshaft position sensor monitoring the speed fluctuations during crankshaft rotation. In a normal four-cylinder engine, ignition and operation cause four slight fluctuations in the crankshaft speed. 2. If the fluctuations decrease, it indicates that a cylinder is not operating or operating poorly. Then, with the help of the camshaft position signal, the specific misfiring cylinder can be identified. 3. When the misfire rate exceeds the limit value, the engine control unit will record the fault code and illuminate the fault light.
As someone who frequently works on car repairs, I often come across the P0304 trouble code, which indicates a misfire in cylinder 4 due to poor ignition. The main causes are usually a faulty ignition coil or worn-out spark plugs—coils degrade over time, leading to weak insulation and reduced current, while spark plugs with excessive carbon buildup cause unstable firing. A clogged fuel injector can also lead to insufficient fuel supply, or there might be compression leaks in the cylinder affecting sealing. During diagnosis, I use a scanner to check the data stream, swap coils to identify the faulty one, and test spark plug resistance. If compression is low, a pressure gauge helps measure it, and vacuum leaks in hoses can also have a big impact. Ignoring repairs leads to severe engine shaking, poor acceleration, skyrocketing fuel consumption, and long-term damage to the catalytic converter, costing even more. It's best to get a professional diagnosis at a reputable shop without delay.
When working on my car at home, I encountered a P0304 code indicating a misfire in cylinder 4. I first tried replacing the spark plugs since they're cheap and easy to change. When that didn't help, I checked the ignition coil - if the multimeter showed high resistance, it meant the coil was bad. Sometimes clogged fuel injectors can be cleared with cleaner spray, or it might just be loose wiring or connectors not properly seated. Compression leaks are less common, but if the head gasket is damaged, professional tools would be needed. After fixing it, the engine immediately ran smoother and fuel consumption dropped. DIY saves money, but you need proper tools and shouldn't disassemble randomly to avoid damaging the car. Regular maintenance prevents this - like changing spark plugs every 2-3 years and cleaning fuel injectors periodically. Safety should never be taken lightly.
