P0307 on Ford: How to Diagnose & Fix
Cylinder 7 Misfire Detected
3 Ford models · 3 documented issues · 2 critical · $150-$1,500 repair
P0307 on Ford by model: symptoms, diagnosis and fix
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.
Common Symptoms
- Loud popping sound
- Misfire
- Loss of power
- Spark plug shoots out of engine
How to Fix
Sources for this issue (1)
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.
Common Symptoms
- Loud popping noise from engine
- Spark plug and coil found on top of engine
- Engine misfire on one cylinder
- Hissing noise from plug hole
- Loss of power and rough running
How to Fix
If a spark plug has blown out, a thread repair kit (Time-Sert or Heli-Coil) can permanently restore the threads without removing the cylinder head ($150-400 per plug at a shop). Prevention: Use anti-seize on spark plug threads, torque to exactly 22-25 ft-lbs (do not overtighten), and avoid changing plugs when the engine is hot. Time-Sert inserts are considered the superior repair ($30-50 per kit DIY). Some shops specialize in this repair and can do it in 30-60 minutes per plug.
Sources for this issue (1)
The optional 4.6L 2-valve modular V8 (shared with the Mercury Mountaineer) has aluminum heads that engage only a few spark-plug threads (~0.25 in). Under thermal cycling the plug can strip the threads and eject from the head, sometimes blowing out the coil boot with it. Ford acknowledged the stripped/missing-thread condition in TSB 07-21-2 for 1997-2008 4.6/5.4/6.8L 2V engines. Ejection causes a loud pop, sudden misfire and power loss, and a fuel-vapor fire risk.
Common Symptoms
- Loud pop/bang followed by exhaust-like ticking
- Sudden misfire and power loss
- Ejected spark plug and/or coil boot in the engine bay
- Check engine light with cylinder misfire code
- Fuel/burning smell (fire risk)
How to Fix
Repair the stripped port with a heli-coil-style thread insert designed for the job — a Time-Sert or Ford's authorized LOCK-N-STITCH aluminum insert kit — rather than replacing the head where possible. Reinstall a new plug and coil boot to spec torque. Prevent recurrence by torquing plugs correctly and anti-seizing per updated practice; inspect all plugs when one lets go.
Sources for this issue (1)
P0307 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0307 mean on a Ford?
P0307 stands for "Cylinder 7 Misfire Detected." P0307 means the engine computer detected a misfire on cylinder number 7 — that cylinder isn't burning its air/fuel mixture completely or at the right moment. The PCM senses this by watching for tiny slowdowns in crankshaft speed each time cylinder 7 should fire. A misfire wastes fuel, can dump raw fuel into the exhaust, and may damage the catalytic converter over time, which is why a persistent or severe misfire often makes the check engine light flash. You may feel rough idle, shaking, hesitation, or a loss of power. On Ford it is documented across 3 models: Crown Victoria, Expedition, Explorer.
What are the most common causes of P0307?
The most common causes of P0307 are: Worn, fouled, or incorrectly gapped spark plug on cylinder 7, Failed ignition coil or coil-on-plug for cylinder 7, 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. The specific cause varies by vehicle.
How much does it cost to fix P0307 on a Ford?
Published repair estimates on Ford range from $150 to $1,500 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0307 on a different make?
View P0307 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.