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P0308 — Cylinder 8 Misfire Detected

Generic OBD-II · all makesPowertrain (engine & transmission)

P0308 indicates that the engine control module has detected an abnormal number of misfires on cylinder 8. A misfire means that cylinder is not consistently contributing power because ignition, fuel delivery, air charge, or mechanical compression in that cylinder is compromised.

Symptoms

What causes it — most likely first

1. Ignition system fault on cylinder 8

Worn or fouled spark plug, a failing ignition coil, or a damaged plug wire/coil boot are the most common reasons a single cylinder sets P0308.

2. Fuel injector or fuel delivery problem

A clogged, leaking, or electrically failing injector can starve or over-fuel cylinder 8, producing a misfire that follows the injector if it is moved to another cylinder.

3. Low compression in cylinder 8

Worn rings, leaking valves, a damaged piston, or a head-gasket breach can reduce compression enough to cause repeated misfires on one cylinder.

4. Air or vacuum leak affecting cylinder 8

An intake manifold gasket leak, cracked vacuum hose, or faulty intake valve sealing near cylinder 8 can upset the air/fuel charge and trigger a misfire.

5. Wiring or connector issue

Poor continuity, corrosion, or shorting in the coil, injector, or cam/crank sensor circuits for that cylinder can interrupt normal firing.

6. Powertrain control module failure

A faulty PCM/ECM is a rare cause of an isolated P0308; it should only be considered after ignition, fuel, mechanical, and wiring causes have been ruled out.

How it's diagnosed

  1. Confirm the code and freeze-frame data, then check for related misfire or fuel/ignition codes.
  2. Inspect and, if possible, swap the cylinder 8 spark plug and ignition coil/wire to another cylinder to see if the misfire moves with the component.
  3. Test the cylinder 8 fuel injector by listening for operation, checking resistance, and swapping it to another cylinder if practical.
  4. Perform a compression test on cylinder 8 and compare it to adjacent cylinders and manufacturer specifications.
  5. Inspect wiring and connectors for the coil, injector, and relevant sensors for damage, corrosion, or poor grounds.
  6. Consider PCM/ECM diagnosis only after all ignition, fuel, mechanical, and wiring causes have been eliminated.

Code facts & related codes

SystemPowertrain (engine & transmission)
StandardizationSAE generic — identical on every make
Related codesP0300 — Randommultiple Cylinder Misfire DetectP0301 — Cylinder 1 Misfire DetectedP0302 — Cylinder 2 Misfire DetectedP0303 — Cylinder 3 Misfire DetectedP0304 — Cylinder 4 Misfire DetectedP0305 — Cylinder 5 Misfire Detected

Vehicles this code applies to

The definition is universal; the diagnostics are engine-specific. Open your vehicle for the codes documented for it:

2002 Ford Thunderbird

Frequently asked

Is it safe to drive with a P0308 code?

Driving is not recommended if the check engine light is flashing, because unburned fuel can damage the catalytic converter. A steady light means limited driving is usually possible, but the fault should be diagnosed soon.

Can I just replace the ignition coil on cylinder 8?

If testing shows the misfire follows the coil when it is moved to another cylinder, replacing that coil is reasonable. Replacing parts without diagnosis can waste money if the root cause is fuel, compression, or wiring.

Do I need to replace all spark plugs and coils when only cylinder 8 misfires?

Not necessarily. It is wise to inspect all plugs and coils for wear, but you should only replace components that testing shows are faulty or worn beyond specification.

Could a bad PCM be causing P0308?

PCM failure causing a single-cylinder misfire is uncommon. Most P0308 cases are caused by ignition, fuel, compression, or wiring issues. The PCM should be the last thing suspected, not the first.