P0308 on Ford
Cylinder 8 Misfire Detected
P0308 on Ford vehicles indicates cylinder 8 misfire detected. Au7o has documented this code across 3 Ford models — most commonly on Crown Victoria, E-Series, Expedition. P0308 means the engine computer detected a misfire on cylinder number 8 — that cylinder is failing to combust properly or at the correct time. The PCM identifies it by monitoring crankshaft speed variations as cylinder 8 fires. Misfires waste fuel, increase emissions, and can overheat and damage the catalytic converter, so a hard misfire may cause a flashing check engine light. Typical symptoms include rough idle, vibration, hesitation, and reduced power. Typical repair costs on Ford range from $150 to $1,500, depending on the specific model and root cause.
Common Causes of P0308
- •Worn, fouled, or incorrectly gapped spark plug on cylinder 8
- •Failed ignition coil or coil-on-plug for cylinder 8
- •Faulty, clogged, or leaking fuel injector
- •Vacuum or intake air leak affecting that cylinder
- •Low compression (worn rings, burnt/leaking valve, head gasket)
- •Damaged spark plug wire or boot (on applicable engines)
- •Carbon buildup or sticking valve
P0308 on Ford by Model
Ford Crown Victoria(1 issue)
- 4.6L 2-Valve Spark Plug Ejection/Breakage1992-2011
The 4.6L 2-valve engine uses spark plugs that thread into aluminum heads with only a few threads of engagement. The plugs can eject from the head under load, stripping the threads. Later models (2004+) use a 2-piece plug design that can break during removal.
Ford E-Series(1 issue)
- Triton 2-Valve Spark Plug Blow-Out from Cylinder Head1997-2008
The 2-valve Triton engines (4.6L, 5.4L, 6.8L V10) used in 1997-2008 E-Series vans are notorious for spark plugs ejecting from the cylinder heads. Ford used only 4 threads in the aluminum heads to secure the spark plugs, which is insufficient to withstand combustion pressures. The plug strips the threads and blows out of the head, often taking the ignition coil with it. This can happen without warning and leaves the vehicle running on fewer cylinders. The problem is most common on plugs 4 and 8 (passenger side).
Ford Expedition(1 issue)
- 5.4L 2-Valve Spark Plug Blow-Out From Cylinder Head1997-2008
The 5.4L Triton 2-valve V8 in 1997-2008 Expeditions is notorious for spark plugs ejecting from the aluminum cylinder heads. The 2-valve heads have only 4 threads holding each spark plug, which is insufficient for the clamping force needed. Over time, the threads strip and the spark plug launches out of the head under combustion pressure, taking the ignition coil with it. This typically happens when spark plugs are removed and reinstalled, or spontaneously at high mileage.
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View P0308 across all makes →Frequently Asked Questions
What does P0308 mean on Ford?▼
P0308 stands for "Cylinder 8 Misfire Detected." P0308 means the engine computer detected a misfire on cylinder number 8 — that cylinder is failing to combust properly or at the correct time. The PCM identifies it by monitoring crankshaft speed variations as cylinder 8 fires. Misfires waste fuel, increase emissions, and can overheat and damage the catalytic converter, so a hard misfire may cause a flashing check engine light. Typical symptoms include rough idle, vibration, hesitation, and reduced power. On Ford specifically, this code is documented across 3 models.
What causes P0308 on Ford vehicles?▼
Common causes on Ford: Worn, fouled, or incorrectly gapped spark plug on cylinder 8, Failed ignition coil or coil-on-plug for cylinder 8, Faulty, clogged, or leaking fuel injector, Vacuum or intake air leak affecting that cylinder, Low compression (worn rings, burnt/leaking valve, head gasket). Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0308 on a Ford?▼
Repair costs on Ford range from $150 to $1,500, depending on the specific model and root cause.
Which Ford models have P0308 documented?▼
Au7o has documented P0308 on 3 Ford models: Crown Victoria, E-Series, Expedition.