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?
- Limited driving only
- 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.
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
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.
What actually makes the computer set a misfire code?
The OBD II regulation defines two separate misfire thresholds (Title 13 CCR 1968.2, section (e)(3.2)). One is misfire severe enough to damage the catalyst, evaluated in 200-revolution increments — and where the damaging rate would be under five percent, the manufacturer may simply set the limit at five percent. The other is misfire causing emissions to exceed 1.5 times the FTP standards. That is why a flashing light (catalyst-damage rate) means stop driving while a steady light for the same code does not. This is the threshold the monitor is designed around, not a description of your specific fault — the regulation says what the system must detect, not how to find it on your vehicle.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
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Swap cylinder 8 coil and spark plug to confirm the misfiring component.
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Injector balance test on cylinder 8.
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Compression and leak-down test if needed.
Sources 2
This page is built from documented references. Verify against your own service info before repair work.
- California Code of Regulations, Title 13 section 1968.2 (OBD II)malfunction criteria, section (e)
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
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:
Commonly Affected Vehicles
- Ford F-150 Expedition (4.6L, 5.4L V8)
- Chevrolet Silverado, Tahoe, Suburban (V8)
- Dodge Ram 1500 (5.7L HEMI)
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