P0307: Cylinder 7 is misfiring
Cylinder 7 Misfire Detected
Cylinder 7 is misfiring. If the light is flashing, stop driving: the catalytic converter is being damaged in real time. If the light is steady, get it checked today.
Stop driving and get help if
- The check engine light is flashing
- The temperature gauge runs high, or you see steam (overheating)
- The car loses power, hesitates badly or stalls
- You smell burning or see smoke
- A brake warning light comes on, or the brakes feel different
Pull over as soon as you can, turn the engine off, and call a tow or roadside help.
What it means
P0307 only appears on V8, V10, or V12 engines. Cylinder 7 is typically on the driver-side bank toward the rear, which places it near the firewall on most rear-wheel-drive trucks and cars. The misfire itself is the same failure as any other single-cylinder code: incomplete combustion sends unburned fuel into the exhaust. What is different about cylinder 7 specifically is that on many V8 trucks, cylinder 7 shares a bank with cylinder 5 and access involves removing exhaust manifold heat shields or working around the transmission bellhousing.
Common causes
- Failed ignition coil on cylinder 7Swap it with an adjacent coil to confirm before purchasing a replacement.
- Worn spark plug on cylinder 7Rear bank plugs on V8 trucks often go longer between services due to difficult access.
- Failed fuel injector on cylinder 7A balance rate test on a scan tool can confirm whether the injector is supplying correct fuel volume.
- Compression loss on cylinder 7Burned valve or worn piston rings. A compression or leak-down test is required to confirm.
What the fix could involve
From the cheaper fix to the bigger one. Prices depend on your car, your area and the shop, so ask for a written quote that names the part and the labor before you approve it.
- Spark plug set
- Ignition coil (one)
- Fuel injector (one)
- Compression repair
Symptoms
- Check engine light flashing or steady
- V8 vibration at idle, noticeably uneven
- Reduced power, especially noticeable in a truck under load
- Fuel economy drop
- Possible P0207 injector fault code alongside
What to do next
On most GM or Ford V8 trucks, cylinder 7 is at the rear of the driver bank. Confirm the cylinder location for your specific engine before reaching for tools. Coil swap first, plug inspection second. If a balance rate test is available on your scan tool, run it to check injector flow while you are diagnosing. A compression test should be part of the diagnosis if ignition and injection both test good.
Lewis reads P0307 alongside any other misfire codes and shows live fuel trims and ignition timing, so you have a clearer picture of what the engine is doing. Get Lewis on the App Store or Google Play.
Related codes
FAQ
- Is P0307 ever caused by a bad crankshaft sensor?
- Rarely on just one cylinder. A failing crank sensor usually causes random misfires on multiple cylinders (P0300). A single-cylinder code almost always points to that cylinder's own components.
- Can spark plug wire problems cause P0307?
- On older vehicles with spark plug wires. Most modern vehicles use coil-on-plug setups, where each coil sits directly on the plug with no wire.
- The truck runs fine at highway speed but misfires at idle. Is that still urgent?
- Yes. The misfire may be less severe at speed because load conditions change. But it is still damaging the converter and will likely worsen.
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