P0308: Cylinder 8 Misfire Detected

Overview

P0308 indicates a misfire event isolated to cylinder 8 where the engine’s combustion process is incomplete or absent, often caused by issues in ignition, fuel delivery, or mechanical engine condition and diagnosable via scan tools, spark/coil tests, and compression checks.

Common Symptoms

• Rough or uneven idle
• Engine hesitation or jerking during acceleration
• Illuminated check engine light
• Reduced engine power and acceleration
• Poor fuel economy
• Fuel smell due to unburned fuel

Most Common Causes

Diagnostic Steps

1. Connect professional OBD-II scan tool and read codes
   Expected: P0308 stored and other related misfire codes visible
   Interpretation: Confirms misfire for cylinder 8 and identifies if other cylinders are also affected.
2. Inspect spark plug, ignition coil, and wiring for cylinder 8
   Expected: Look for fouling, cracks, corrosion, or damage
   Interpretation: Damaged or worn ignition components can be root cause if visibly compromised.
3. Swap ignition coil (and optionally spark plug) with another cylinder
   Expected: Misfire follows the component if defective
   Interpretation: If misfire code moves, swapped component is faulty.
4. Check fuel injector function via balance test or swap with another injector
   Expected: Pressure drop or misfire change when swapped
   Interpretation: Indicates injector or control circuit issues if misfire moves.
5. Perform vacuum leak test around intake and manifold
   Expected: Smoke or pressure test reveals leak
   Interpretation: Leak near cylinder 8 intake runner can cause lean misfire.
6. Perform cylinder compression test
   Expected: Compression values similar to other cylinders
   Interpretation: Low compression indicates mechanical failure requiring further engine work.

Repair Solutions

Frequently Asked Questions