Cylinder 8 Misfire Detected
The P0308 code means the vehicle's onboard diagnostic system has detected: Cylinder 8 Misfire Detected. This is a serious severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- medium
- Estimated cost
- $8-$30 per spark plug; $30-$80 per coil
The #1 fix for misfire codes. 15-piece set with 14mm, 16mm, 18mm magnetic sockets, T-handle extension, and spark plug gapper.
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Read and clear misfire codes. Shows which cylinder is misfiring so you know exactly what to replace.
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Common Symptoms
- Rough idle on V8 engine
- Check Engine Light on
- Power loss
Probable Causes (Ranked by Likelihood)
- Faulty spark plug on cylinder 8 Very High
- Failed ignition coil on cylinder 8 High
- Clogged fuel injector on cylinder 8 High
- Low compression on cylinder 8 Moderate
Step-by-Step Diagnostic Procedure
-
Swap cylinder 8 coil and spark plug to confirm the misfiring component.
-
Injector balance test on cylinder 8.
-
Compression and leak-down test if needed.
Common Fixes by Vehicle
What techs usually find when diagnosing P0308 on specific vehicles — tap your vehicle for the fix and the exact part:
2009-2020 Ford F-150 5.0L/5.4L V8 easy DIY
Cylinder 8 misfire on Ford V8s usually traces to the coil-on-plug or the spark plug for that cylinder. Coil swap-test confirms it fast. On 5.4L 3V engines, watch for the known spark-plug-seizing issue — soak with penetrating oil and pull when the engine is warm. Check for a vacuum leak if multiple cylinders flag.
Labor: 30-60 minFrequently Asked Questions
I have both P0300 and P0308: what does that mean?
A random/multiple misfire (P0300) combined with a specific cylinder code (P0308) means the random misfire may be driven primarily by cylinder 8. Fix cylinder 8 first and see if P0300 resolves as well.
Sources
This page is built from documented references. Verify against your own service info before repair work.
P0308 on Diesel, EV & Equipment
The same code ID appears across other engines and platforms. The diagnostic flow varies by manufacturer — these are the platform-specific breakdowns:
See All Codes & Fixes for Your Vehicle
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