Cylinder 8 Misfire Detected
P0308 indicates that the engine control module (ECM) has detected a misfire in cylinder 8. A misfire occurs when the air-fuel mixture in the cylinder fails to ignite properly, causing a loss of power, increased emissions, and potential damage to the catalytic converter. Common causes include faulty spark plugs, ignition coils, fuel injectors, low compression, or vacuum leaks. Prompt diagnosis is recommended to prevent further engine damage.
1. Most Common Causes
- Worn or damaged spark plug
- Deteriorated spark plug wire with abnormal resistance
- Clogged or electrically faulty fuel injector
- Defective ignition coil (in coil-on-plug systems)
- Burnt intake or exhaust valve, or carbon buildup
- Low compression in cylinder 8 (rings, valves, head gasket)
- Faulty ignition control module (ICM) or injector driver
- Short, open circuit, or excessive resistance in injector or coil wiring
- Contaminated fuel or incorrect fuel pressure
- Vacuum leak at cylinder 8 intake port
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Engine runs rough or misfires, especially at idle or under load
- Reduced power and acceleration
- Increased fuel consumption
- Possible engine vibration or shaking
3. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data to confirm P0308 and check for other codes.
Step 2: Visually inspect spark plug and ignition coil on cylinder 8; swap coil with another cylinder to see if misfire moves.
Step 3: Test fuel injector on cylinder 8 using a noid light or multimeter; check for proper spray pattern.
Step 4: Perform a compression test on cylinder 8; compare to other cylinders.
Step 5: Check for vacuum leaks using a smoke machine or propane enrichment method.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive with a misfire, as it can damage the catalytic converter and other engine components. Limit driving to short distances and low speeds until repaired.
How much does it cost to fix?▼
The cost varies depending on the cause. A spark plug or coil replacement can cost $50-$150, while fuel injector or compression repairs can range from $200 to $1,000 or more.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.