Parts
$8–120
P0307 — Cylinder 7 Misfire Detected
CAUTIONIs it safe to drive? Drivable to a shop, but don't ignore it — misfires dump raw fuel into the exhaust and destroy catalytic converters quickly; stop immediately if the CEL flashes.
What P0307 means
The ECM detected repeated incomplete combustion events in cylinder 7. On V8 engines cylinder 7 is typically rear passenger side; on flat engines it can be awkward to access. Root causes are the same as any misfire.
Most likely causes (in order)
- Spark plug (inspect condition before replacing anything else)
- Ignition coil or coil pack for cylinder 7
- Fuel injector clogged or circuit fault
- Vacuum leak near cylinder 7 intake port
- Compression loss from worn rings or burned valve
Symptoms you might notice
- engine vibration
- rough idle
- loss of power
- poor fuel economy
- black smoke from exhaust
What to check first
Use a scan tool that shows misfire counts per cylinder in live data — watch whether misfire counts climb at idle, under load, or at a specific RPM. Load-only misfires point to injector or compression; idle-heavy misfires point to spark/coil.
Repair cost & difficulty
Labor
0.5–2.5 hr
Difficulty
DIY-friendly