I replaced the spark plugs and the misfire came back on cylinder 4. What next?

Swap the ignition coil. If the misfire follows the coil, that is your answer. If not, check the injector and then compression.

On a V6, where is cylinder 4?

V6 cylinder numbering varies by manufacturer. On many GM V6 engines, cylinder 4 is the front cylinder on the passenger bank. Check your engine diagram.

Can a bad crankshaft sensor cause P0304 on just one cylinder?

Unlikely. A bad crank sensor causes random or multiple misfires across all cylinders, which would set P0300. A single-cylinder code almost always points to that cylinder's specific components.

Codes › P0304

P0304: Cylinder 4 is misfiring

Cylinder 4 Misfire Detected

High severityCan you keep driving?

If the light is flashing, stop driving and get towed. If it is steady and you feel shaking, drive carefully to a shop today. Do not run a misfiring engine longer than necessary.

What it means

P0304 means cylinder 4 is not combusting properly. On a four-cylinder engine, cylinder 4 is the farthest from the engine's ancillary components, and its coil and injector harnesses are often routed around hot or sharp-edged areas. A misfire here produces the same exhaust risk as any other cylinder misfire: unburned fuel in the exhaust that overloads the catalytic converter. On V6 and larger engines, cylinder 4 is often closer to the firewall, where heat soak and tight spaces make access and diagnosis slower.

Common causes

Failed ignition coil on cylinder 4Swap the coil with another cylinder to confirm. Coil failure is the most statistically common cause.
Worn or damaged spark plug on cylinder 4Check the electrode. A worn or cracked plug often causes intermittent misfires that worsen over time.
Cylinder 4 fuel injector failureElectrical fault or clogging. Check for P0204 in the code list.
Low compression on cylinder 4Burned valve or worn rings. Compression test is definitive.

What it costs

Spark plug set$80 to $250
Ignition coil (one)$150 to $400 installed
Fuel injector (one)$150 to $400 installed
Compression repair$900 to $3,500

Symptoms

Check engine light flashing or steady
Rough idle and vibration
Hesitation and power loss
Fuel economy drop
Possible P0204 injector fault alongside this code

What to do next

Start by swapping the cylinder 4 coil with cylinder 3. If the misfire moves to cylinder 3, replace the coil. If it stays on cylinder 4, check the plug. On tight-access V-engines, getting to cylinder 4 may require removing intake components. Budget extra labor if the cylinder is buried. Do not skip the compression test if ignition parts check out clean.

Lewis shows cylinder 4 misfire counts and coil dwell time simultaneously so you can see whether the ignition system is even attempting to fire the cylinder. Download Lewis.

Related codes

FAQ

I replaced the spark plugs and the misfire came back on cylinder 4. What next?: Swap the ignition coil. If the misfire follows the coil, that is your answer. If not, check the injector and then compression.
On a V6, where is cylinder 4?: V6 cylinder numbering varies by manufacturer. On many GM V6 engines, cylinder 4 is the front cylinder on the passenger bank. Check your engine diagram.
Can a bad crankshaft sensor cause P0304 on just one cylinder?: Unlikely. A bad crank sensor causes random or multiple misfires across all cylinders, which would set P0300. A single-cylinder code almost always points to that cylinder's specific components.