What does it mean?
P1304 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Cylinder 4 Misfire Detected . This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms
- MIL (check engine lamp) on and flashing when the misfire is heavy; a flashing lamp means stop driving to protect the catalytic converter
- Rough, shaking idle that smooths slightly at higher rpm
- Loss of power and a stumble when pulling away or accelerating
- Fuel smell, black smoke and worse fuel consumption
- Uneven exhaust beat with occasional popping
Likely causes
- Spark plug 4 worn out, oil fouled or with an incorrect gap
- Breaking-down ignition coil or a split boot arcing to the head on cylinder 4
- Injector 4 restricted, leaking or not being driven electrically
- Vacuum leak at the number 4 intake runner or a leaking injector seal
- Low compression on cylinder 4: burnt valve, worn rings, tight valve clearance or head gasket leakage
- Low fuel pressure, contaminated fuel or a heavily restricted air filter
- Wiring or connector fault at coil or injector 4, often heat related
How to fix it
- Verify with live misfire counters that the counts belong to cylinder 4 and read the freeze frame conditions
- Swap coil 4 with an adjacent cylinder's coil, clear codes and see whether the misfire follows
- Repeat the swap with the injector if the coil is not the cause
- Inspect spark plug 4 for wear, oil, coolant traces and correct gap
- Smoke test the intake around runner 4 and check the injector seal
- Check fuel pressure and test injector 4 for correct resistance and spray pattern
- Carry out a compression test, followed by a leak-down test on cylinder 4 if compression is down