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P0308 Cylinder 8 Misfire Detected

Cylinder 8 specifically is failing to burn its fuel properly — the computer has isolated the problem to that one cylinder.

Misfire & ignition

The ECU tracks crankshaft acceleration after each firing event. When cylinder 8 fails to contribute, the crank slows measurably at that point in the rotation, and the ECU counts the event. Enough counts and it sets P0308. The useful thing about a single-cylinder code is how much it narrows the search: whatever is wrong is almost certainly a part that belongs to cylinder 8 alone — its coil, its plug, its injector, or its compression — rather than something the whole engine shares. That is what separates this from a P0300.

Diagnose P0308 on your specific vehicle Add your year, make and model for ranked causes, repair videos and the exact parts you need

Can I keep driving?

Driveable

If the light is flashing, stop driving — that flash means converter damage in progress, and a converter costs several times what the misfire repair does. With a steady light, keep trips short and gentle until it's fixed.

How serious

Moderate to high. A dead cylinder pumps unburned fuel into the exhaust, and that fuel lights off in the catalytic converter and cooks it. A flashing check-engine light means that damage is happening now.

Symptoms you'll notice

What causes P0308

Ordered by what to check first — how likely each cause is, weighed against what it costs to rule out. Working down the list in order is what stops you replacing an expensive part to fix a cheap problem.

01

Failed ignition coil on cylinder 8

On a coil-on-plug engine this is the most common single-cylinder cause. The coil for cylinder 8 is a self-contained part, which is precisely why the fault stays on one cylinder. It is also the easiest thing in this list to confirm — see the swap test below.

02

Worn or fouled spark plug in cylinder 8

Cheap, and worth pulling regardless because the plug's appearance is diagnostic in itself. Oil-fouled points at valve seals or rings; fuel-soaked points at a leaking injector; a cracked insulator or a gap worn wide is simply an old plug.

03

Clogged or failed fuel injector on cylinder 8

An injector that is blocked, stuck, or electrically dead starves only its own cylinder. If the coil and plug both test good, this is the next stop. A stethoscope on the injector body will tell you whether it is clicking.

04

Vacuum leak local to that cylinder

A cracked intake runner gasket or a split hose feeding cylinder 8 leans out that cylinder alone. Less common than the electrical causes but cheap to find with a smoke test.

05

Low compression in cylinder 8

The expensive answer: a burnt exhaust valve, worn rings, or a head gasket leak. Test for it once the cheap causes are eliminated — but a compression test that comes back low stops you from buying parts that will not help.

06

Damaged wiring to the coil or injector

A chafed wire or a corroded connector at that one cylinder mimics a failed component exactly. Inspect the connector before ordering the part.

How to diagnose it

  1. Swap the ignition coil from cylinder 8 with the one from cylinder 7, clear the codes, and drive it. If the misfire follows to P0307, the coil is bad and you're done diagnosing. This test costs nothing and is the single most useful thing you can do with this code.
  2. If the code stays on cylinder 8, swap the spark plug the same way and repeat.
  3. Pull the plug from cylinder 8 and read its condition — oil-fouled, fuel-soaked, or simply worn each point somewhere different.
  4. Listen to the injector for cylinder 8 with a mechanic's stethoscope or a long screwdriver; a silent injector is a dead one. Check its resistance against the others on the rail.
  5. If coil, plug and injector all check out, run a compression test on cylinder 8 and compare it against its neighbours. A cylinder more than about 10% below the others is a mechanical problem, not an electrical one.
  6. If compression is low, a leak-down test tells you where it's going: hissing at the intake means an intake valve, at the exhaust an exhaust valve, into the crankcase means rings.

Parts you might need

Tools for the job

Related trouble codes

Get the parts list for your vehicle Ranked causes, tutorials and live part prices for your exact year, make and model

Fitment matters. Causes and parts above are the common cases for P0308 across vehicles. The specific part numbers, procedures and torque specs vary by year, make, model and engine — always confirm against service data for your vehicle before buying parts or starting work.