P0308: Cylinder 8 is misfiring

Cylinder 8 Misfire Detected

What it means

P0308 is a cylinder 8 misfire, which only appears on V8 or larger engines. Cylinder 8 is typically the last cylinder on one bank, usually at the rear of the passenger-side bank on most American V8s. It is often the hardest cylinder to access on the entire engine. More importantly, cylinder 8 on a rear-wheel-drive V8 sits near the firewall, where heat soak is greatest and wiring harnesses get pinched by the engine mount or routed near sharp edges. A coil or plug failure there is easy to overlook simply because access is so poor.

Common causes

1. Failed ignition coil on cylinder 8The most common cause. Rear-bank coils on V8s see more heat and are often not inspected during routine service.
2. Worn spark plug on cylinder 8Cylinder 8 is often the last plug replaced on a V8 because of access difficulty. It ends up the most worn.
3. Wiring harness damage near the cylinder 8 coil or injectorThe harness near the rear of the passenger bank contacts the firewall and is prone to chafing.
4. Failed fuel injector on cylinder 8Confirm with a balance rate test. P0208 will often be stored alongside.
5. Low compression on cylinder 8A compression or leak-down test is the definitive check.

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 on, flashing or steady
• V8 idle that sounds loping or uneven
• Loss of power under load
• Vibration felt through the seat and steering wheel
• Possible P0208 injector code alongside

What to do next

Confirm cylinder 8 location on your specific engine. Swap the coil with a known good cylinder and road test. On vehicles where cylinder 8 access is extremely limited, have a shop perform the coil swap to avoid damaging nearby components. If the coil and plug check out, test the injector before moving to compression testing.

Lewis reads P0308 alongside misfire codes for every cylinder, so you can confirm cylinder 8 is the only one flagged before tearing into a tight-access repair. Get Lewis on the App Store or Google Play.

Related codes

• P0300
• P0307
• P0420

FAQ

Which side is cylinder 8 on a GM V8?

On most GM small-block V8s, the odd cylinders (1, 3, 5, 7) are on the driver side and even cylinders (2, 4, 6, 8) are on the passenger side. Cylinder 8 is the rearmost passenger-side cylinder.

Can a collapsed lifter cause P0308 on just one cylinder?

Yes. A collapsed lifter on cylinder 8 causes low compression and a misfire on that cylinder only, and it will not respond to coil or plug replacement. A compression test will catch it.

I cleared the code and it came back in 20 minutes. What does that mean?

It means the misfire is consistent, not intermittent. The underlying fault is active every time the engine runs. The coil swap test is your fastest path to a diagnosis.