P0308 — Engine misfire detected in cylinder number eight

A misfire in cylinder 8 means that part of the engine isn’t firing properly, causing rough running and reduced power. It happens when the air-fuel mixture in that cylinder fails to ignite correctly, often due to ignition, fuel, or mechanical issues. The engine control unit detects this and stores the code to help diagnose the problem.

Common causes

The cause is almost always one of a few things. Here they are — P0308 rarely comes from anything outside this list:

• Faulty spark plug in cylinder 8
• Bad ignition coil or wire for cylinder 8
• Fuel injector clogged or failing on cylinder 8
• Compression problems like worn valves or piston rings
• Vacuum leaks near cylinder 8

Where to start

In the order a sensible mechanic would work — the cheap checks first, the expensive replacements only after:

1. Check and replace spark plug in cylinder 8
2. Test and swap ignition coil or wires if faulty
3. Clean or replace fuel injector for cylinder 8
4. Perform compression test and repair engine if needed
5. Inspect and fix vacuum leaks around cylinder 8

That is what holds for P0308 in general. From here it depends on your engine — tell me which car it is and what it does, and I will give you the steps for it: real procedures, torque figures and diagrams instead of general advice.