Where is cylinder 4 on my engine?

On a 4-cylinder inline engine, cylinder 4 is the last cylinder, usually at the rear of the engine near the firewall. On a V6, cylinder 4 is commonly the first position on Bank 2. On a V8, cylinder 4's location depends on the manufacturer — Ford and GM differ. Check the engine layout diagram for your specific engine.

Can I keep driving with P0304?

If the light is flashing, stop driving when safe. On a 4-cylinder engine, losing one of four cylinders is severe — the engine will run very rough. With a steady light, drive directly to a shop and avoid hard acceleration.

Does P0304 mean my engine needs major work?

Usually no. Most P0304 cases are a single failed spark plug, ignition coil, or fuel injector — none of which are major work. Internal engine damage is the worst-case scenario but is uncommon on well-maintained engines. The swap test resolves the diagnosis quickly.

How much does P0304 cost to fix?

Most fixes land between $50 and $400. Compression-related repairs start at $1,000. On a 4-cylinder engine, the affected cylinder is usually easy to access, keeping labor low.

OBD-II trouble code

P0304: Cylinder 4 Misfire Detected

The engine computer detected a misfire specifically in cylinder 4. On a 4-cylinder engine, this is the last cylinder; on V engines, position varies by manufacturer. The check engine light may be flashing; pull over if it is.

Quick facts

System: Powertrain
Category: Ignition and Misfire
Severity: High severity
Drivable: Usually safe to drive short-term
Repair cost range: $50 – $1,500
DIY difficulty: Intermediate DIY

What does P0304 mean?

A misfire is a cylinder that fails to combust properly. The engine control module (ECM) detects misfires by monitoring crankshaft speed — a healthy combustion event accelerates the crankshaft slightly, and the ECM watches for the missing acceleration that signals a failed combustion event. When the ECM isolates the misfire to a single cylinder, it sets a cylinder-specific code instead of the generic P0300.

P0304 means the misfire is in cylinder 4. On a 4-cylinder inline engine, cylinder 4 is the last cylinder, typically at the rear of the engine near the firewall. On a V6, cylinder 4 is often the first cylinder on Bank 2 in many configurations. On a V8, cylinder 4 may be on either bank depending on the manufacturer — Ford and GM use different numbering. Check the engine service information for the exact position.

A flashing check engine light during P0304 indicates the misfire is active. Unburned fuel reaches the catalytic converter and can damage it quickly. Pull over safely if the light is flashing. If the light is steady, you can drive directly to a shop, but avoid hard acceleration and don't ignore the code for days.

Common causes

Worn or fouled spark plug in cylinder 4
Failing ignition coil for cylinder 4 (most common on coil-on-plug engines)
Faulty fuel injector for cylinder 4 (stuck, clogged, or leaking)
Low compression in cylinder 4 from a burned valve, worn rings, or head gasket leak
Cracked or damaged spark plug wire feeding cylinder 4 (older engines)
Carbon buildup on the intake valve for cylinder 4
Vacuum leak isolated to the cylinder 4 intake runner
Improperly installed or wrong-gap spark plug

Symptoms

Check engine light on or flashing
Rough idle and engine shaking
Loss of power on acceleration
Hesitation or stumble
Poor fuel economy
Smell of unburned fuel from the exhaust
On a 4-cylinder engine, noticeably running on three cylinders

Diagnostic steps

1.Confirm the code is P0304 alone — companion misfire codes can indicate a broader fuel, vacuum, or ignition issue.
2.Inspect the spark plug in cylinder 4. Compare its condition to the other plugs.
3.Swap the ignition coil from cylinder 4 with a known-good coil. Clear the code and drive. If the misfire follows the coil to its new cylinder, that coil is bad.
4.Repeat with the spark plug.
5.Test the cylinder 4 fuel injector resistance and confirm pulsing.
6.If ignition and fuel test fine, perform a compression test on cylinder 4.

Repair cost

$50 – $1,500

Single spark plug $10 to $30 plus 15 to 30 minutes of labor. Ignition coil $40 to $200 plus brief labor. Fuel injector $100 to $400 plus 1 to 3 hours. On 4-cylinder engines, cylinder 4 is often easy to reach at the rear of the engine. On V engines, access depends on the bank and engine bay layout. Compression-related repairs $1,000 and up.

Estimate your repair

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DIY vs shop

This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.