Ford F150 P0304 Code: Causes, Diagnosis & Repair Steps for Cylinder 4 Misfire
Hello. I own a 2007-2010 Ford F150 with a 4.6L V8 engine. The check engine light is on and the diagnostic scan shows code P0304, indicating a misfire in cylinder #4. I've already replaced the spark plugs for that cylinder, which was found to be dirty and damp. Despite this, the vehicle still runs with a rough idle. I'm currently replacing all spark plugs and coil-over boots as part of a broader maintenance effort. However, I'm unsure what other components or checks are necessary to resolve this issue. As someone not experienced in repairing older vehicles, I'm feeling frustrated but seeking practical advice on next steps. What should I inspect or replace beyond the spark plugs? Any guidance would be greatly appreciated.
A misfire can stem from: 1) Ignition system – Check if the spark plug is actually sparking; try swapping the coil to see if the code moves to a different cylinder. 2) Injector – Verify that the fuel injector is pulsing; use a noid light. A lean condition may be present, which could be addressed with additives like SeaFoam or Techron. 3) Mechanical issues – Perform a compression test and inspect for vacuum leaks, especially around cylinder #4. Note: Cylinder #4 is located on the passenger side rear of the engine.