P0304: Cylinder 4 Misfire — Causes and Fixes
Key Takeaway
P0304 targets cylinder 4. Here's the diagnosis checklist.
P0304 = Cylinder 4 Misfire
| Check | What to Look For | Cost to Fix |
|---|---|---|
| Spark plug | Worn electrode, oil fouling | $20 – $40 |
| Ignition coil | Weak or no spark | $50 – $150 |
| Fuel injector | Restricted flow | $150 – $300 |
| Valve seal | Oil burning in cylinder | $500 – $1,500 |
| Compression | Low reading on cyl 4 | $1,000+ |
Cylinder 4 Notes
On inline-4 engines, cylinder 4 is at the end and may have different heat characteristics. Some engines are more prone to coil failure on this cylinder.
Diagnosis
Use the swap test: move coil to another cylinder, clear code, drive. If misfire follows the coil = bad coil. If it stays = spark plug, injector, or internal issue.
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