2012 Ford F150 5.0L Engine P0308 Code: Diagnosing Intermittent Misfire on Cylinder 8

Are there any additional diagnostic codes present? P030x misfire codes can stem from several sources: - Ignition system: Is the spark plug firing correctly? Are all coil and plug connectors securely tightened? - Fuel injection: Check for proper fuel injector connector integrity—could missing clips be an issue? - Mechanical factors: Verify engine compression and look for vacuum leaks. What was the appearance of the old #8 spark plug? Was it wet, dry, black, or tan in color? Note: Cylinder #8 is on the driver's side rear (back cylinder).

All connections are tight. The previous #8 spark plug showed a tan color, indicating partial combustion. I also confirmed that cylinder #8 is located on the driver’s side rear of the engine.

No other codes either.

A simple and low-cost fix to try: Add one can of Sea Foam or Techron fuel additive to half a tank of fuel. This may help clean carbon deposits from the injectors and improve combustion efficiency, especially in older engines.

JohnK123 wrote: My 2012 Ford F150 with a 5.0L V8 engine is experiencing an intermittent misfire on cylinder #8, which triggers the P0308 diagnostic trouble code (DTC). I have already replaced the spark plug, coil pack, and fuel injector for cylinder #8. After resetting the ECU, the vehicle runs smoothly for about one day before the check engine light returns. The issue persists even after multiple resets. Cylinder #8 is located on the driver's side rear of the engine (back cylinder). I'm looking for cost-effective troubleshooting steps before visiting the dealership. Any insights or common fixes would be greatly appreciated. - John K This issue has affected me in the past, and about a month ago it started again—this time with a rough idle on cylinders #4 and #8. After investigation, I found that water from my hood (due to missing liner) had entered the spark plug holes of those cylinders. The moisture caused short circuits in the coil packs, leading to misfires. To resolve this, I removed each coil pack, applied a small amount of dielectric grease, and reinstalled the hood liner. A key step is to check for water ingress inside the spark plug wells—this can be a common but overlooked cause in older trucks with exposed engine compartments.