Parts
$8–150
P0308 — Cylinder 8 Misfire Detected
CAUTIONIs it safe to drive? Get it checked soon — a single misfiring cylinder is drivable short-term, but the catalytic converter is the expensive victim if you delay; a flashing CEL is a stop-now signal.
What P0308 means
Cylinder 8 is missing combustion events. On most V8 layouts this is the rear driver-side cylinder — sometimes buried under wiring or vacuum lines. Diagnosis follows the same swap-and-test logic as any cylinder misfire.
Most likely causes (in order)
- Spark plug worn, cracked, or oil-fouled
- Coil-on-plug unit (swap with cyl 7 and recheck)
- Fuel injector — stuck closed or wiring issue
- Intake or exhaust valve burned (compression test will reveal this)
- Head gasket seepage between cylinder 8 and coolant jacket
Symptoms you might notice
- rough idle
- vibration
- poor acceleration
- fuel smell from exhaust
- flashing check engine light
What to check first
Perform a relative compression test with a scan tool (engine cranking, no start) — it measures RPM dips per cylinder as each fires. A cylinder 8 dip pinpoints compression loss without pulling the head; costs nothing if you have a capable scanner.
Repair cost & difficulty
Labor
0.5–3 hr
Difficulty
DIY-friendly