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, or low compression. This code is often accompanied by rough idling, hesitation, and the check engine light flashing.
01. Most Common Causes
- Faulty spark plug or ignition coil on cylinder 8
- Clogged or leaking fuel injector on cylinder 8
- Low compression due to worn piston rings, valves, or head gasket
- Vacuum leak affecting cylinder 8
- Engine control module (ECM) or wiring issue
02. Symptoms You Will Notice
- Check engine light flashing or steady
- Rough idle or engine shaking
- Loss of power and hesitation during acceleration
- Increased fuel consumption
- Engine may run rough or stall
03. Step-by-Step Diagnosis
Step 1: Scan for codes and note freeze frame data to confirm P0308.
Step 2: Inspect spark plug and ignition coil on cylinder 8; swap with another cylinder to see if misfire moves.
Step 3: Check fuel injector on cylinder 8 for proper operation using a noid light or injector tester.
Step 4: Perform a compression test on cylinder 8 and compare to other cylinders.
Step 5: Inspect for vacuum leaks using a smoke machine or propane enrichment.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive with a misfire, especially if the check engine light is flashing, as it can damage the catalytic converter and other engine components. Have it diagnosed and repaired promptly.
How much does it cost to fix?▼
The cost varies depending on the cause. Replacing a spark plug or ignition coil typically costs $50-$150 per part plus labor. Fuel injector replacement can be $150-$400. Compression repairs can be significantly more.