P3363 — Cylinder 2 misfire detected, CNG/LPG mode

P3363 points at engine misfire (cylinder 2). The standard definition names the system involved; which part inside it has actually failed is what the checks below establish, cheapest first.

Common causes

The cause is almost always one of a few things. Here they are — P3363 rarely comes from anything outside this list:

• Worn or fouled spark plugs
• Failed ignition coil on that cylinder
• Injector blocked or leaking
• Loss of compression — worn valve or head gasket
• Unmetered air leaking into the intake

Where to start

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

1. Swap the coil with a neighbouring cylinder and see whether the misfire follows it — this identifies a coil fault in minutes and costs nothing
2. Pull the plug on that cylinder and read its condition
3. Swap the injector the same way if the misfire stayed put
4. Check for vacuum leaks around the intake
5. Compression-test the cylinder if the electrical and fuel sides are both good

That is what holds for P3363 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.