OBD-II Code · Powertrain
P0308
Cylinder 8 Misfire Detected
Severity
high
Left alone, this one tends to take other parts with it.
Can you drive it
Depends on the light
Flashing: stop as soon as it is safe to — raw fuel is reaching the catalytic converter. Steady, and it only feels rough: a short drive to a shop is usually fine. Either way, stop if it shakes hard, loses power, overheats or makes a new noise.
Indicative cost (USD)
$30–$400
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
Plug/coil first
Cylinder 8 misfire. V8 only.
How a shop works this
The ECU has already told you which cylinder. That makes the fastest honest test a swap: move one part to another cylinder and see whether the fault moves with it. It identifies the fault instead of guessing at it, and it costs nothing.
Photograph the coils before you touch anything, and note which is which.
Cylinder numbering is not the same across manufacturers, and V6 and V8 bank layouts differ by maker — look up the firing order and bank layout for your engine before you move parts, or you can spend an hour swapping coils on the wrong bank.
Move the cylinder 8 ignition coil to a cylinder that is not misfiring, put that cylinder's coil on 8, clear the code, and run it until the misfire returns.
On a modern coil-on-plug engine the coil is the most common single answer to a cylinder-specific misfire, which is why it is the first thing to move — not because it is the cheapest part. A misfire that is there even at idle is the classic dead-coil pattern.
- The misfire follows the coil to its new cylinderThe coil is the fault. Replace it. If the engine has real mileage on it, the other coils are on the same clock.
- The misfire stays on cylinder 8The coil is fine. Look at the coil connector and the harness around it next — chafed and rodent-damaged connections at that plug are a common second answer — then pull the plug.
Read the plug you pulled, and check the boot for carbon tracking.
Black and sooty means it has been running rich. White or blistered means lean or too hot. Oil-wet points at valve seals or rings. Fuel-wet points at an injector holding open. A carbon-tracked boot arcs to the head and imitates a dead coil for the price of a new boot. On an older engine with a distributor, the cap, rotor and plug wires belong in this step too.
If spark is accounted for, go to fuelling, then to compression.
An injector balance or flow test comes first because it is quicker. Compression test second: a cylinder more than about 15% below its neighbours is mechanical, and no ignition part will fix it. A vacuum leak on this one runner sits alongside these — a leak big enough to affect every cylinder would be setting P0300 instead.
A flashing check-engine light means the misfire is putting raw fuel into the catalytic converter, which can destroy it quickly. Stop driving as soon as it is safe to. A steady light with a mild misfire is less urgent, but stop anyway if it shakes hard, loses power, overheats, or makes a noise it was not making before.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Rough idle
- Check engine light
- Heavy shake at idle
Likely causes
- Failed ignition coil (cylinder 8)Most common
- Damaged coil connector or harness at cylinder 8
- Worn spark plug or carbon-tracked boot (cylinder 8)
- Clogged or leaking fuel injector (cylinder 8)
- Low compression on cylinder 8
- Vacuum leak at the cylinder 8 intake runner
Read the full diagnostic procedureP0308 means cylinder 8 is misfiring, restricting the diagnosis to V8s, V10s, and V12s.
P0308 means cylinder 8 is misfiring, restricting the diagnosis to V8s, V10s, and V12s.
Standard misfire flow
- plug read, coil swap with an adjacent same-bank cylinder, plug swap, compression test, injector flow test.
- Cylinder 8 is typically the rear-most cylinder on one bank, which makes it the hardest to access on most longitudinal V8s — on a Ford modular 4.6L/5.4L, cylinder 8 is the rear-most cylinder on the left (driver's) bank, sitting partway under the cowl.
- On a GM LS V8, cylinder 8 is the rear-most cylinder on the left (driver's) bank.
- On a Chrysler Hemi, cylinder 8 is the rear-most cylinder on the left bank.
- The rear cylinders on a longitudinal V8 are exposed to the most heat soak and the longest exhaust manifold runs, which means they fail coils, plugs, and exhaust manifold studs first — budget extra labor on a P0308 just to get to the part.
Vehicle-specific patterns2004-2010 Ford F-150/Expedition/Navigator 5.4L 3V Triton is the most common P0308 in North America — same triple-threat as the other left-bank misfir…
- 2004-2010Ford F-150/Expedition/Navigator 5.4L 3V Triton is the most common P0308 in North America — same triple-threat as the other left-bank misfires (stuck plugs, cam phaser rattle, carbon-tracked coil boots), with the added wrinkle that cylinder 8 is buried under the cowl and adds 0.5-1.0 hr of labor over the front cylinders.
- 2007-2014GM 5.3L/6.0L with Active Fuel Management throws P0308 from collapsed AFM lifters on the deactivated cylinders.
- 2003-2008Dodge Ram/Durango 5.7L Hemi commonly throws P0308 from a known exhaust manifold bolt failure on the rear-most cylinders, causing a localized exhaust leak that confuses the O2 sensor into commanding a lean condition specifically on cylinder 8.
- 2006-2010Mercedes-Benz M273 5.5L V8 throws P0308 from the same balance-shaft wear pattern as P0306.
Estimated repair$80 (single coil + extended labor) to $4,500+ (AFM delete or balance-shaft on the M273).
Look up another code
P0308 — frequently asked
What does a P0308 code mean?
Cylinder 8 misfire. V8 only.
What causes a P0308 code?
Common causes: Failed ignition coil (cylinder 8); Damaged coil connector or harness at cylinder 8; Worn spark plug or carbon-tracked boot (cylinder 8); Clogged or leaking fuel injector (cylinder 8); Low compression on cylinder 8; Vacuum leak at the cylinder 8 intake runner.
What are the symptoms of a P0308 code?
Typical symptoms: Rough idle; Check engine light; Heavy shake at idle.
Is it safe to drive with a P0308 code?
Depends on the light. Flashing: stop as soon as it is safe to — raw fuel is reaching the catalytic converter. Steady, and it only feels rough: a short drive to a shop is usually fine. Either way, stop if it shakes hard, loses power, overheats or makes a new noise. Estimated repair: $30-$400 — plug/coil first.
How do I diagnose a P0308 code?
The ECU has already told you which cylinder. That makes the fastest honest test a swap: move one part to another cylinder and see whether the fault moves with it. It identifies the fault instead of guessing at it, and it costs nothing. 1. Photograph the coils before you touch anything, and note which is which. 2. Move the cylinder 8 ignition coil to a cylinder that is not misfiring, put that cylinder's coil on 8, clear the code, and run it until the misfire returns. 3. Read the plug you pulled, and check the boot for carbon tracking. 4. If spark is accounted for, go to fuelling, then to compression.
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