P0304 Error Code: An In-depth Analysis

An engine is a fine-tuned machine with several car sensors and components that works in synergy for a seamless operation. One cannot help but marvel at how some vehicles switch to “God mode” on the highway. However, car engines suffer occasional breakdowns or malfunctions.

One of the common issues your vehicle engine can encounter is misfiring. The symptoms are easily identified by almost anyone, especially when the car computer throws error codes on the car memory. The diagnostic trouble code shows which cylinders are misfiring.

One of the prominent trouble codes indicating cylinder misfiring is the P0304. Here, an Rx mechanic expert has outlined the causes, symptoms, diagnostics mistakes, and the severity of an OBD P0304. You’ll also learn how to diagnose and proffer solutions to this problem. Let’s start with defining and explaining the code, and what do P0304 on Hyundai and other car models mean?

What the P0304 code means

What does error code P0304 mean?

A P0304 diagnostic trouble code means the powertrain control module has detected a misfire on cylinder four. Engine misfire occurs when the engine combustion process is compromised in a given, multiple, or random cylinder. In the case of a P0304, there’s a compromised combustion process on the no.4 cylinder.

The car computer, also known as the powertrain control module (PCM) or engine control module (ECM), logs the misfire error code in accordance with the data received from the crankshaft position sensor. As the internal combustion cycles, any malfunctioning cylinder will lead to a drop in the crankshaft rotational speed.

The crankshaft position sensor will notify the car computer of the misfire, and the PCM will throw a corresponding error code and project the check engine light on the dashboard.

What is the symptom of error code P0304?

There are several symptoms to be alert and not wait for get P0304 cylinder 4 misfires detected. While the signs of a P0304 ford code may differ from a P0304 Toyota code, some symptoms are prevalent across all car models.

Here are the common signs of a P0304 error code you should watch out for.

Check engine light

There’s no doubt that the car computer displays the check engine light on the dashboard whenever it detects a misfire on any cylinder. The check engine light notifies the driver of an imminent issue that needs urgent attention. Remember that several issues can cause the powertrain control module to trigger the engine warning light on the instrument cluster.

Poor gas mileage

If the cylinder-four injector is spraying excess fuel, it’ll lead to high fuel consumption and cause the engine control module to throw error code P0304 on BMW or your respective car model. In addition, issues like P0300, P0301, and several other problems can lead to bad gas mileage.

Hard starting

Another common sign of a P0304 on VW and other cars is hard starting. A car engine is a fine-tuned machine that works in sync for a seamless operation. This means all the cylinders and other systems should work as predetermined by the manufacturer. If any cylinder is dead or not functioning as it should, it can cause hard starting.

Lack of power

If the engine eventually starts, it’ll lose power, especially when driving. Depending on the root cause of the problem, the throttle pedal may feel unresponsive.

Rough idle

Most misfires are prevalent on idle. By this, your vehicle may run rough on a sitting point but runs smoothly or close to normal when you hit the highway.

The gas smell from the tailpipe

A bad spark plug and lousy fuel injector that is spraying excess fuel can cause ‘rich’ smelling exhaust. Let’s make it clearer; if the no.4 cylinder spark plug is dead, it won’t burn all the fuel on that cylinder properly. The unburnt fuel will escape through the exhaust tailpipe as the exhaust valve opens, causing fuel odor from the tailpipe.

Similarly, if the cylinder four fuel injector sprays too much fuel, the spark plugs may not burn all the fuel. In such cases, the unburnt fuel will escape through the tailpipe, causing a gas smell from the tailpipe.

Other symptoms of P0304 on Honda and other car models you may encounter include

  • Hesitant acceleration
  • Stalling at idle.

What causes Cylinder 4 Misfire P0304?

There are several probable causes of a P0304 error code. However, the most common causes are fuel or spark delivery issues. Here are potential causes you should navigate to when tracking the culprits.

How serious is error code P0304?

A P0304 error is a serious issue and should be rectified on time. In most cases, this happens when the engine control unit detects unburnt fuel in the no.4 cylinder. The unburnt fuel has the tendency to foul or clog the catalytic converter.

I know you don’t want a common issue like a lousy spark plug to cause eventual failure on other related components. Therefore, you should track the root cause of the problem and fix it as soon as possible.

How to diagnose

Several parameters like a faulty injector, vacuum leaks, leaking head gasket, etcetera can cause the ECM to throw P0304 on Chevy Silverado or your respective car model. Therefore, you’ll need a walkthrough guide if you need to diagnose and fix the problem at home. 

Diagnosis is time-consuming and labor-intensive for inexperienced DIYers. It also requires several tools to track and fix the root cause.

Items and Tools Needed

  • Screwdrivers
  • Pliers
  • Scan tools
  • Leakdown tester
  • Compression tester
  • Plug spanner
  • Fuel pressure gauge
  • Socket, ratchet, and extension
  • Spark plugs
  • Spark plug wires
  • Digital Multimeter

Step 1: Scan the vehicle

Locate the OBD2 port underneath the steering wheel and connect the scan tool. After that, scan the vehicle and pull out the registered error codes. If there are other logged codes, fix them before moving to the next level. You may likely see error codes like P0300, P0301, P0302, P0303, P0305, or P0306.

Don’t worry if you’re unfamiliar with how to run a scan check with an OBD2 scan tool. Check out this article on how to use an OBD2 scan tool for a simplified walkthrough.

Step 2: Inspect the connectors and wires

Inspect the injector and spark wiring connectors on cylinder four. Tighten or replace any loose, damaged, or frayed wires and connectors, and do not forget to check the ground wires. This can cause random or multiple engine misfires.

Step 3: Examine the Spark plugs and injectors

Lousy spark plugs or faulty injectors usually cause a P0304 on Ford F150 and other car models. This step is so simple but requires rapt attention. So, follow this guide religiously.

If you have individual ignition coils or spark plug wires, start by swapping the cylinder-four coil or plug wire with no.1 or another one that works properly. Then, check if the misfire remains on that cylinder or if it transfers to the next cylinder. The plug wire or ignition coil is bad if the misfire transfers to the other cylinder.

In the same manner, swap the no.4 injector with any cylinder that’s working correctly. Check if the issue remains on no.4 cylinder or transfers with the injector. If the issue transfers, that’s an indication that the injector is bad. Also, repeat the same swap with the plugs or clean them.

The following articles will be helpful for this diagnosis

Step 4: Conduct a leak down or compression test

If the injector and spark plug test checks out, you need to narrow it down to compression or leak-down tests. With this test, you can determine if any internal mechanical problems are causing the misfire on cylinder four. Here are some internal mechanical problems that can cause a P0304 fault code.

Common P0304 diagnosis mistakes

The most common P0304 diagnostics mistake of is not completing every diagnosing step and replacing unnecessary parts. To prevent these mistakes, follow the diagnosing procedures religiously and do not replace any parts unless it is bad.

Fouled spark plugs, damaged plug wires, and lousy injectors are most likely the root cause of P0304 on many vehicles. However, do not replace any component without a thorough diagnosis.

How do you fix P0304?

Now, how do I fix code P0304? Since many issues can cause the ECM to throw error code P0304 on your vehicle, it will need one or more of the following repairs to proffer a solution to the issue.

  • Cleaning or replacing spark plugs
  • Replacing spark plug wires, coil packs, and/or distributor cap.
  • Repairing vacuum leaks
  • Fixing fuel delivery issues
  • Repair of internal mechanical faults.

How much does it cost to fix a cylinder 4 misfire?

The P0304 error can come from a fouled spark plug to a defective fuel injector to vacuum leaks. You can’t give accurate information without a thorough diagnosis.

If you choose to have a certified mechanic track and fix the root cause, the technician will start with an hour of diagnosis. Most repair shops charge $75 to $150. Most of these shops will add the diagnosing fee to the repair cost if you have them to proffer solutions to the problem.

After a thorough diagnosis, the repair shop should be able to give you an accurate P0304 repair cost. After a proper diagnosis, one or more of the following should be the culprit. The prices below include the parts price and the labor fee. Kindly note that the price may be more depending on your location and car model.

  • Spark plugs $65 to $250
  • Spark plug wire $40 to $100
  • Fuel injector $150 to $300
  • Ignition coil $75 to $300
  • Vacuum leaks $100 to $200.

P0304

FAQs:

Can you drive with a cylinder 4 misfire?

Yes, you can drive with a misfiring engine as long as you want. However, the engine power will reduce and may die when stopping, depending on the severity of the problem and how many cylinders you have.

For instance, If no.4 cylinder drops on a four-cylinder engine, the engine will suffer more than when it happens on a six-cylinder or eight-cylinder engine. Here’s why I said so; when one cylinder drops in an eight-cylinder, you have a 12.5% loss of engine power, and when that happens in a four-cylinder, you have a 25% loss of engine power.

Therefore, the impact depends on how many cylinders you have. However, driving with an engine misfire can be dangerous and even lead to engine damage.

Can a misfire correct itself?

If there’s water on the ignition system, it can prevent sparks on the corresponding line, causing misfires. But as soon as the water dries off, the misfire will disappear. However, engine misfire will not correct itself unless external engine components cause them. Even when they disappear, they’ll likely come back until you track and fix them.

Is a misfire easy to fix?

Fixing a misfire is an easy repair task that may repair cleaning or replacing a spark plug or plug wires. However, some complicated issues like internal mechanical problems may be the culprit. Therefore, it is best to have a certified mechanic track the root cause and proffer solutions.

Will a tune-up fix a misfire?

No doubt, a tune-up is a preventive maintenance, but it can fix engine misfires. While many may have a different opinion about this, think of the causes of engine misfires and what a service technician should cover during a tune-up.

An engine tune-up involves diagnosing, checking, and changing fouled spark plugs, plug wires, fuel filters, injectors, and oil filters, amongst other things. Replacing fouled spark plugs can be all you need to rectify a misfire.

Which cylinder is P0304?

P0304 means cylinder-four misfire detected. If the car computer throws a P0304 error code, it signifies the cylinder-four is misfiring. If your scan tool pulls out only this error code, other cylinders are firing correctly. Therefore, when running the diagnosis, you need to pay attention to that cylinder.

Final Words

Whether a spirited or regular driver, you will always desire a seamless driving experience. But unfortunately, engine misfires are one of those dreaded but inevitable engine issues that’ll happen when you least expect it.

This article has explained everything you need to know about a P0304 engine misfire, from the causes to symptoms to how to track and rectify the problem. Follow the guides religiously if you want to track and fix the issues at home. However, diagnosis and repairs are not recommended for inexperienced DIYers. Contact your mechanic if you do not trust your guts.

Osuagwu Solomon

Osuagwu Solomon is a seasoned automotive technician for the past 9 years, and a technical writer. He loves writing about auto professional repair guides, DIY repair guides, and buyer’s guide. After spending six years in the automotive workshop, he decided to impact his knowledge to people aside his domain, and he has achieved this by centering his Automotive writing skills on REPAIRS.

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