P0308 Chevy Silverado: Cylinder 8 Misfire Diagnosis and Fix

P0308 on a Chevy Silverado means cylinder 8 is misfiring — the rearmost cylinder on the passenger side of the engine. Cylinder 8 is the most difficult to access on a GM V8, located near the firewall on the passenger side. It’s not an AFM cylinder, which simplifies diagnosis to coil, plug, injector, and compression.

Watch a cylinder-specific misfire traced to a failed ignition coil — the same plug, spark and coil checks apply to P0308.

Cylinder 8 Location

Passenger side cylinders front-to-rear = 2, 4, 6, 8. Cylinder 8 is the rearmost cylinder on the passenger side — the fourth cylinder back on the passenger bank, near the firewall. Access to the coil and plug requires reaching over or around the engine — on some Silverado configurations you may need to remove the intake duct or other components for comfortable access.

Common Causes

Failed ignition coil on cylinder 8, worn spark plug, defective fuel injector. Cylinder 8 is NOT an AFM deactivation cylinder (AFM uses 1, 4, 6, 7 on the 5.3L). Standard ignition diagnosis applies. Because cylinder 8 is harder to access, some technicians and DIYers delay the repair — a persistent misfire on any cylinder will damage the catalytic converter over time, so prioritize diagnosis even if access is more challenging.

Access Tips for Cylinder 8

On most Silverado 1500s, reaching cylinder 8 from above is feasible with a long extension and universal joint on your ratchet. Remove the engine appearance cover if present. The coil connector on cylinder 8 can be difficult to release — use a small flathead to depress the tab while pulling. From below with the truck on ramps, some techs prefer to access the plug through the wheel well area on the passenger side.

Diagnosis

Swap the cylinder 8 coil to cylinder 6. If P0306 sets, replace the cylinder 8 coil. Inspect and replace the plug. If coil and plug are good, test injector function and run compression. Related codes: P0300, P0306, P0304.