OBD-II · Engine and powertrain (P)
P0304
Cylinder 4 misfire detected
What it means
The ECU has detected misfires on cylinder 4 from small drops in crankshaft speed. Cylinder numbering follows the manufacturer's scheme; if the warning light flashes, reduce load and stop soon to protect the catalytic converter.
Symptoms
- rough idle or shaking, often worse when cold or under load
- hesitation, jerking or loss of power when accelerating
- engine warning light; if it flashes, the misfire is severe enough to overheat the catalytic converter
- higher fuel consumption
Likely causes, most likely first
| No. | Cause |
|---|---|
| 01 | failing ignition coil on that cylinder |
| 02 | worn, cracked or fouled spark plug |
| 03 | clogged or leaking fuel injector |
| 04 | oil in the spark plug well from a leaking valve cover or plug tube seal |
| 05 | LPG injector fault for that cylinder on converted cars |
| 06 | low compression (valve, piston ring or head gasket problem) |
What to check, step by step
- 01Confirm the misfire with the per-cylinder misfire counters in live data
- 02Swap the cylinder 4 ignition coil with a neighbouring cylinder, clear codes and re-test: if the misfire moves, replace the coil
- 03Remove and inspect the spark plug for wear, cracks, wrong gap, fouling or oil in the plug well
- 04Have a workshop test the injector. Direct-injection swapping requires OEM depressurisation, replacement seals and coding where specified; compare petrol/LPG operation where applicable.
- 05Do a compression test on cylinder 4 if ignition and fuel check out