P0307 – Cylinder 7 Misfire Detected means the engine control unit has identified that cylinder 7 is not firing correctly. A misfire in a single cylinder can lead to rough idle, hesitation, reduced power, increased fuel consumption, and potential catalytic converter damage if ignored. This fault can be caused by ignition issues, fuel delivery problems, airflow errors, or mechanical failures. This guide explains what P0307 means, its symptoms, causes, diagnosis steps, and the most effective fixes to restore proper engine performance.
What Does P0307 Mean?
P0307 is a generic OBD-II diagnostic trouble code indicating that the ECU has detected a misfire occurring specifically in cylinder 7. The ECU monitors crankshaft speed changes and cylinder power contribution. When cylinder 7 produces insufficient combustion power or misfires repeatedly, P0307 is stored in memory.
Misfires must be addressed promptly because unburned fuel can enter the exhaust and overheat the catalytic converter, causing expensive damage.
Quick Reference
- OBD-II Family: P-Code (Powertrain)
- Scope: Generic
- System: Ignition / Fuel / Air / Mechanical
- Difficulty Level: Easy–Moderate
- Estimated Repair Cost: €50–€350+
- Last Updated: 5 December 2025
Real-World Example / Field Notes
A large V8 SUV arrived with a strong vibration at idle and poor acceleration. Scan data showed cylinder 7 misfiring consistently. Inspection revealed a cracked ignition coil boot causing spark leakage to the valve cover. Replacing the coil and spark plug completely resolved the issue.
Another case involved a pickup truck misfiring only under heavy load. The fuel injector for cylinder 7 had restricted flow, resulting in a lean misfire at high RPM. Professional injector cleaning restored full functionality and eliminated P0307.
Symptoms of P0307 – Cylinder 7 Misfire Detected
- Rough idle: Noticeable shaking or engine vibration.
- Loss of power: Hesitation, stumbling, or reduced acceleration.
- Poor fuel economy: Misfires waste fuel and reduce combustion efficiency.
- Check engine light: Flashing or steady depending on severity.
- Fuel smell: Unburned fuel entering the exhaust system.
- Engine stalling: Severe misfires may cause intermittent stalling.
Common Causes of P0307
Most Common Causes
- Worn or fouled spark plug in cylinder 7
- Faulty ignition coil or coil boot
- Clogged or leaking fuel injector (cylinder 7)
- Vacuum leak near intake runner for cylinder 7
- Dirty or failing mass airflow (MAF) sensor
Less Common Causes
- Low compression from valve, piston, or ring wear
- Failing camshaft or crankshaft position sensor
- Fuel pressure too low due to pump or regulator issues
- ECU internal driver fault (rare)
- Carbon buildup affecting cylinder 7 combustion
Diagnosis: Step-By-Step Guide
Diagnosing P0307 requires checking the ignition system, fuel delivery, intake system, and mechanical health of cylinder 7.
Tools You’ll Need
OBD-II scanner with misfire counters, spark tester, multimeter, fuel pressure tester, compression gauge, smoke machine, and standard hand tools.
- Review freeze-frame data: Note the conditions during the misfire (RPM, load, coolant temp).
- Inspect spark plug: Check for cracks, carbon buildup, fouling, or oil deposits.
- Swap ignition coils: Move coil 7 to a different cylinder; if the misfire follows, the coil is faulty.
- Test fuel injector: Perform an injector balance test or swap injectors to compare performance.
- Check for vacuum leaks: Smoke-test intake areas near cylinder 7.
- Clean or test MAF sensor: A failing MAF can cause lean misfires.
- Check fuel trims: Positive trims suggest air leaks; negative trims may indicate injector leakage.
- Test fuel pressure: Verify pump and regulator performance.
- Perform compression test: Low compression confirms mechanical engine issues.
- Verify cam/crank timing signals: Incorrect timing may cause intermittent misfires.
Pro Tip: On V6 and V8 engines, rear-bank cylinders like cylinder 7 often run hotter and wear ignition components faster. Always inspect coil boots carefully.
Possible Fixes & Repair Costs
- Replace spark plug (cylinder 7): €20–€60
- Replace ignition coil: €50–€120
- Clean or replace fuel injector: €120–€250
- Repair vacuum leak: €50–€150
- Clean or replace MAF sensor: €20–€150
- Repair mechanical engine issues: €300–€900+
Can I Still Drive With P0307?
Driving with P0307 is not recommended. A misfiring cylinder can send unburned fuel into the exhaust, causing the catalytic converter to overheat. If the MIL is flashing, continuing to drive can cause severe engine or catalyst damage.
Related Codes
- P0399 – Ignition Coil “R” Primary/Secondary Circuit
- P0364 – Reserved
- P0363 – Misfire Detected Fueling Disabled
- P0362 – Ignition Coil “L” Primary/Secondary Circuit
- P0361 – Ignition Coil “K” Primary/Secondary Circuit
- P0360 – Ignition Coil “J” Primary/Secondary Circuit
- P0359 – Ignition Coil “I” Primary/Secondary Circuit
- P0358 – Ignition Coil “H” Primary/Secondary Circuit
- P0357 – Ignition Coil “G” Primary/Secondary Circuit
- P0356 – Ignition Coil “F” Primary/Secondary Circuit
Key Takeaways
- P0307 means cylinder 7 is misfiring and requires prompt diagnosis.
- Most common causes: spark plug, ignition coil, injector, or vacuum leak.
- A flashing MIL means severe and catalyst-damaging misfires.
- Most repairs are quick and inexpensive when caught early.
FAQ
What is the most common cause of P0307?
The most common cause is a failing ignition coil or worn spark plug in cylinder 7.
Can a vacuum leak cause cylinder 7 misfires?
Yes. A leak near the intake runner for cylinder 7 creates a lean condition that triggers misfires.
Is it safe to drive with P0307?
No. Driving with this code risks severe catalytic converter damage and unsafe drivability.
How do I know if the injector is faulty?
Swap injectors between cylinders or use an injector balance test to confirm injector problems.
Should I replace one ignition coil or all of them?
You can replace just the faulty one, but on high-mileage engines replacing coils in sets can prevent future failures.