P0308: Cylinder 8 Misfire Detected
The engine computer has detected misfires in cylinder 8, which exists on V8 and larger engines.
What P0308 means
P0308 points the finger at cylinder 8, so your vehicle has a V8 or larger engine. The computer has seen the crankshaft slow down repeatedly at the moment cylinder 8 should have fired. On older V8s with plug wires, the last cylinders are often closest to the exhaust manifold and firewall, where wires get cooked and start leaking spark to ground. On newer engines with coil-on-plug ignition, a failed coil or oil in the plug well is more likely. A mechanic will compare misfire counts across cylinders, swap coils or wires, look at the plug, and test the injector. If spark and fuel are good, a compression test checks for a valve, lifter or ring problem. A single cylinder misfire on a V8 is easy to ignore because the engine still feels strong, but it is wasting fuel and heating the catalytic converter. Fix it before it turns into a converter or engine repair.
Common symptoms
- Check engine light on, or flashing when the misfire is bad
- Rough or shaky idle
- Hesitation or jerking when you accelerate
- Loss of power, especially going uphill or merging
- Worse gas mileage
Most common causes
- Failing ignition coil or plug wire on cylinder 8
- Worn, cracked or oil-fouled spark plug
- Leaking or clogged fuel injector
- Vacuum leak near the rear of the intake
- Lifter or valvetrain problem
- Exhaust manifold leak throwing off the reading on that bank
What to check yourself first
Check plug wire routing on cylinder 8, since wires that touch the exhaust manifold melt and leak spark. On coil-on-plug engines, swap the coil with cylinder 7 or 6 and see whether the code moves. Check for oil in the plug well.
Typical fixes and what they cost
| Fix | Typical cost | Note |
|---|---|---|
| Replace ignition coil | $238-$320 | Confirm with a swap test first. |
| Replace spark plugs | $288-$399 | If plugs are past service life, do the full set. |
| Replace spark plug wires | $246-$335 | Older V8s with plug wires often arc near the exhaust manifold on rear cylinders. |
| Replace fuel injector | $768-$953 | Replaced after it fails a test. |
Typical US price ranges for parts and labor, not quotes. Your shop should confirm the cause with a diagnostic before replacing parts.
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Related codes
- P0300 Random/Multiple Cylinder Misfire Detected
- P0307 Cylinder 7 Misfire Detected
- P0306 Cylinder 6 Misfire Detected
- P0420 Catalyst System Efficiency Below Threshold (Bank 1)
- P0208