If you’re a car owner, then you’re probably familiar with engine codes. These codes can tell you what’s wrong with your car’s engine, which can be incredibly useful for troubleshooting and repairs.
P0304 indicates a misfire in cylinder number 4.
I’m John Cunningham, a qualified mechanic, you are in the right place, and very shortly, you’ll have a good understanding of the cause, the diagnosis process, and the fix.
One of the most common engine codes is P0304. In this post, we’ll cover everything you need to know about P0304, including the following:
We’ll cover the following:
What is P0304?
P0304 is an engine code that indicates a misfire in the fourth cylinder of your engine. Your engine has multiple cylinders that work together to generate power. When one of these cylinders isn’t firing correctly, it can cause a whole host of problems.
P0304 specifically indicates a problem in the fourth cylinder of your engine.
If you’re experiencing P0304, you may notice one or more of the following symptoms:
- Check engine light: The most obvious symptom of P0304 is that your check engine light will come on. This is usually the first sign that something is wrong with your engine.
- Rough idle: If your engine is misfiring, you may notice that your car has a rough idle. This means that your engine is vibrating or shaking when you’re sitting still.
- Poor acceleration: A misfiring cylinder can cause your car to accelerate more slowly than usual. You may notice that your car feels sluggish or that it takes longer to get up to speed.
- Engine sounds rough: If your engine is misfiring, you may notice that it sounds rough or uneven. This could be a sign that one of your cylinders isn’t firing correctly.
- Fuel smell: If your engine is misfiring, you may notice a strong smell of unburned fuel. This could be caused by fuel that’s not being burned correctly in the misfiring cylinder.
- Stalling: In severe cases, a misfiring cylinder can cause your car to stall. This means that your engine will stop running, which can be dangerous if you’re driving.
- Reduced fuel economy: A misfiring cylinder can cause your car to use more fuel than usual. This means that you may need to fill up more frequently than usual, which can be expensive over time.
What causes P0304?
There are several things that can cause P0304, including:
- Bad spark plug: A worn or damaged spark plug can cause your engine to misfire. Over time, spark plugs can become fouled or worn out, which can lead to a misfire.
- Bad ignition coil: Your engine’s ignition coil is responsible for creating the spark that ignites the fuel in your engine. If the ignition coil is bad, it can cause a misfire.
- Clogged fuel injector: Your engine’s fuel injectors are responsible for spraying fuel into the cylinders. If one of these injectors is clogged, it can cause a misfire.
- Vacuum leak: Your engine relies on a vacuum to operate correctly. If there’s a leak in your engine’s vacuum system, it can cause a misfire.
- Low compression: If the compression in your engine’s cylinders is low, it can cause a misfire. This can be caused by worn piston rings or damaged valves.
- Timing issues: If the timing of your engine is off, it can cause a misfire. This could be caused by a problem with your engine’s timing belt or chain.
- Wiring issues: If there’s a problem with the wiring that connects your ignition system or fuel injectors to your engine’s computer, it can cause a misfire.
How to diagnose P0304?
Diagnosing P0304 requires a bit of detective work. Here are the steps you can take to diagnose the problem:
- Check the spark plug: Start by checking the spark plug in the fourth cylinder. If it’s dirty, fouled, or damaged, it could be the cause of the misfire.
- Check the ignition coil: If the spark plug looks fine, check the ignition coil. You can do this by swapping the ignition coil from the fourth cylinder with one from another cylinder. If the misfire moves to the other cylinder, then you know that the ignition coil is the problem.
- Check the fuel injector: If the spark plug and ignition coil look fine, check the fuel injector. You can do this by swapping the fuel injector from the fourth cylinder with one from another cylinder. If the misfire moves to the other cylinder, then you know that the fuel injector is the problem.
- Check the compression: If the spark plug, ignition coil, and fuel injector all look fine, check the compression in the fourth cylinder. Low compression can cause a misfire.
- Check for vacuum leaks: Finally, check for vacuum leaks. You can do this by using a smoke machine or spraying carburetor cleaner around the engine while it’s running. If you see smoke or the engine’s idle changes, then you know that there’s a vacuum leak.
Common fix for P0304
The fix for P0304 depends on what’s causing the misfire. Here are some common fixes:
- Replace the spark plug: If the spark plug is fouled or damaged, replace it.
- Replace the ignition coil: If the ignition coil is bad, replace it.
- Clean or replace the fuel injector: If the fuel injector is clogged, clean or replace it.
- Repair or replace damaged wiring: If there’s a problem with the wiring, repair or replace it.
- Replace the timing belt or chain: If the timing is off, replace the timing belt or chain.
- Replace worn piston rings or damaged valves: If the compression is low, replace worn piston rings or damaged valves.
- Fix vacuum leaks: If there’s a vacuum leak, fix it.
P0304 is a common engine code that indicates a misfire in the fourth cylinder of your engine. If you’re experiencing P0304, you may notice symptoms like a rough idle, poor acceleration, or reduced fuel economy.
Diagnosing the problem requires a bit of detective work, but the fix depends on what’s causing the misfire. By following these steps, you can diagnose and fix P0304 and get your car running smoothly again.
About the Author
This article was created with the assistance of AI technology to aid the author, John Cunningham, who is a seasoned Red Seal-certified auto technician with more than 25 years of experience in vehicle repairs. However, please note that John Cunningham has edited the content to ensure accuracy and quality.
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John Cunningham is an Automotive Technician and writer on Rustyautos.com. He’s been a mechanic for over twenty-five years and has worked for GM, Volvo, Volkswagen, Land Rover, and Jaguar dealerships.
John uses his know-how and experience to write fluff-free articles that help fellow gearheads with all aspects of vehicle ownership, including maintenance, repair, and troubleshooting.