Cylinder 8 Misfire Detected
The powertrain control module (PCM) has detected a misfire originating specifically from cylinder number 8. This is typically identified by monitoring minute variations in the crankshaft rotational speed during the power stroke of that specific cylinder.
A persistent misfire can dump unburned fuel into the exhaust, leading to severe and rapid catalytic converter damage. It should be diagnosed and repaired as soon as possible to prevent costly secondary failures.
Common symptoms
- Flashing or illuminated Check Engine Light
- Rough idle or engine hesitation during acceleration
- Noticeable lack of engine power
- Increased fuel consumption
- Smell of unburned fuel from the exhaust
Likely causes
- Faulty or worn spark plug in cylinder 8
- Defective ignition coil or spark plug wire for cylinder 8
- Clogged, failing, or leaking fuel injector at cylinder 8
- Intake manifold vacuum leak affecting cylinder 8
- Low engine compression in cylinder 8 due to internal engine wear or valve issues
What to check before replacing parts
Inspect the cylinder 8 spark plug and ignition coil or wire for visible damage.
Look for: Look for worn electrodes, carbon tracking, cracked porcelain, or oil/coolant pooling in the spark plug well.
Swap the cylinder 8 ignition coil with the coil from a known good cylinder, clear codes, and test drive.
Look for: If the misfire code moves to the new cylinder, the ignition coil is faulty; if it stays P0308, the coil is likely good.
Test the cylinder 8 fuel injector operation using a stethoscope and a multimeter.
Look for: A lack of rhythmic clicking indicates a stuck injector, while incorrect resistance readings point to an internal electrical failure.
Check for vacuum leaks near the intake manifold runner for cylinder 8.
Look for: Listen for hissing sounds or use a smoke machine to identify smoke escaping from gaskets or hoses near the cylinder.
Perform a compression test and cylinder leak-down test on cylinder 8.
Look for: Compression readings significantly lower than other cylinders (usually more than 15% variance) indicate mechanical issues like burnt valves, worn piston rings, or a blown head gasket.
This page explains the generic P0308 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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