Fix P0307: Mechanic’s solutions that WORKED

The P0307 is one of several misfire codes you can read on your scan tool. I studied 120+ different vehicles with misfires and how were they fixed, to provide you with a list of the most common causes, also with an action plan to diagnose this fault in no time.

You don’t want to delay fixing your P0307 as the misfire will damage your catalytic converters or engine internals. Both of these fixes are priced at thousands of dollars while the misfire is often caused by a worn-out $5 spark plug. Fix it ASAP.

P0307 quick overview

Meaning	P0307: Cylinder #7 Misfire Detected
Is it serious?	Yes, this code is serious and needs immediate attention to prevent damage to the engine or catalytic converter.
Possible causes	-Worn or faulty spark plug in cylinder #7 -Defective ignition coil for cylinder #7 -Malfunctioning fuel injector for cylinder #7 -Internal engine issues (e.g., valve clearance, piston ring wear) -Wiring or electrical connection problems related to cylinder #7
How to diagnose?	Inspect Spark Plug: Check the spark plug in cylinder #7 for signs of wear or damage. Test Ignition Coil: Swap the ignition coil with another cylinder to determine if the misfire moves. Check Fuel Injector: Perform a swap or test of the fuel injector in cylinder #7 to confirm it’s functioning correctly. Perform Compression Test: Conduct a compression test on cylinder #7 to rule out internal mechanical issues. Inspect Wiring: Examine the wiring and connections related to cylinder #7 for any faults or loose connections.

Case study: real cases of solving P0307

I checked specifically for code P0307 and picked these example fixes from my full case study of 123 vehicles with misfires.

How to fix P0307 on Ford

Car: 2001 Ford Expedition XLT 5.4L
Problem: P0307, P0357

Diagnosing: Sparkplugs and coils were changed, and the car passed OK tests for compression, cylinder leakage, and even the fuel injector. However, the funny thing was there was a problem and it was discovered randomly by swapping injector #7 for a new one.
Fix: New fuel injector fixed the problem.

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How to fix P0307 on BMW

Car: 2009 BMW X6 xDrive50i 4.4L
Problem: Poor Idle Quality, Hesitation, Misfire, MIL Lamp on, P0300 – P0305, P0307

Diagnosing: After diagnosing the ignition system and checking the vacuum leaks, the fault was in the fuel system.
Fix: Reprogram injectors + replace the fuel pump.

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How to fix P0307 on Jaguar

Car: 2005 Jaguar S-Type Sport 4.2L
Problem: Misfire, P0300, P0301, P0303, P0305, P0307, P1316

Diagnosing: The technician replaced the coils which seemed to fix the issue on first try.
Fix: Replace ignition coils.

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How to fix P0307 on Toyota

Car: 2002 Toyota Sequoia SR5 4.7L
Problem: Excessive Emissions, Poor Idle Quality, Hesitation, Misfire, MIL Lamp on, P0301, P0303, P0305, P0307

Diagnosing: All the codes were on the one bank and fuel trims on the same bank showed negative -20% values, indicating a problem in the ignition system. All coils and spark plugs were changed on that bank, however, the problem stayed.
Fix: Replace oxygen sensor for OEM unit, aftermarket didn’t work correctly.

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How to fix P0307 on Chevy

Car: 1999 Chevrolet Tahoe LS 5.7L
Problem: Misfire, Loss of power, Check engine light, P0307, P0300

Diagnosing: Changing the oil, filters, and ignition components didn’t fix anything, the problem was hiding in the exhaust valves clearance.
Fix: Rebuild engine heads

The key takeaways from these cases

• Negative fuel trims mean it is trying to correct for a rich condition. Maybe the coolant temperature sensor is sending false info to the PCM. May also be a bad map sensor.
• Remember that new aftermarket (even OEM) parts can come faulty. Don’t forget that in your diagnosing process

P0307 FAQ and conclusion:

Check the Wikipedia article on combustion engines if you are still unsure what exactly the misfire is. Understanding it will help you with your diagnosis.

The key takeaways from these cases

• Don’t change coils/spark plugs unless you confirm they are faulty (do a swap test at least)
• A lot of misfire cases are caused by internal engine damage/timing so don’t rush with replacing ignition/fuel parts without further diagnosis
• Your diagnosing is sometimes right, but only the OEM part will solve the issue