What is an engine misfire?
A misfire happens when a cylinder fails to burn its air-fuel mixture properly. You feel it as a stumble, shake, or loss of power, especially under acceleration or at idle.
Understanding misfire codes
P0300 means random misfires across cylinders. P0301 through P0308 point to a specific cylinder — P0303 is cylinder 3. A specific cylinder narrows the cause to that plug, coil, or injector.
Most common causes
- Worn or fouled spark plugs
- Cracked ignition coil or boot
- Clogged or leaking fuel injector
- Vacuum leak at intake gasket or hose
- Low compression from valve or ring wear
- Bad fuel or water in fuel
How mechanics pinpoint it
A quick trick is swapping the coil from the misfiring cylinder to another. If the misfire follows the coil, the coil is bad. If not, we test the plug, injector, and compression.
Is it safe to drive?
A mild, occasional misfire can be driven gently to repair. A flashing check engine light means raw fuel is overheating the catalytic converter — repairs jump from $200 to $2,000 if ignored.