Cylinder 4 Misfire Detected
The air and fuel mixture is not burning properly in cylinder 4. The engine computer notices because the crankshaft (the shaft the pistons turn) slows down for an instant every time that cylinder misfires. The last digit of the code is the cylinder number.
What the car has detected
The engine computer has counted more failed combustions in cylinder 4 than it allows for the current load and engine speed. It measures this from changes in crankshaft speed.
If the misfire continues, unburnt fuel reaches the catalytic converter and can damage it. If the engine warning light is flashing, the misfire is severe: drive as little as possible and get it to a garage as soon as you can.
Symptoms
- Engine warning light on or flashing
- Rough idle or a shaking engine
- Hesitation and loss of power when accelerating
- Hard starting
- Higher fuel consumption
- Smell of unburnt fuel from the exhaust
Possible causes
- Worn or dirty spark plug (the part that makes the spark)
- Faulty ignition coil or spark plug lead
- Cylinder 4 injector dirty, leaking or with an electrical fault
- Air leak near cylinder 4 (intake hose or gasket)
- Low compression: valves, piston rings or head gasket
- Timing out of adjustment or a faulty crankshaft or camshaft sensor
Checks for the garage
- Read all the codes and the freeze frame data before clearing anything
- Check battery and charging voltage: low voltage upsets ignition and injectors
- Check the cylinder 4 spark plug, coil and wiring; move the coil to another cylinder and see whether the misfire follows it
- Test the cylinder 4 injector and the fuel pressure
- Do a compression test on cylinder 4
- Look for air leaks and intermittent breaks in the wiring
Next step
Avoid hard acceleration and long trips, and have the spark plug, coil, injector and compression of cylinder 4 checked.
Go to a garage if the warning light is flashing, if the engine shakes a lot or loses power, or if the code comes back after replacing the spark plug or coil. Compression and injector tests need workshop tools.