What does the P0300 code indicate on a Ford F-150?

I have a 2016 3.5 Ecoboost with 87,000 miles. I changed the spark plugs after the dealer said it was time. Three months later, my engine started misfiring, showing P0300 codes and misfires in cylinders 5 and 3. I checked the plugs, and the gap looks fine. I bought and replaced all six coil packs. The problem is still there. I added some fuel injector cleaner to the tank, but it didn’t help. Any ideas?


Your truck’s engine is misfiring, and it appears that the spark plugs and coil packs you replaced aren’t the issue. Here are a few possible causes:

  • Engine wear: Internal components such as valves or piston rings may be worn out and require inspection.
  • Faulty spark plug wires: Check the condition of the wires that connect the spark plugs (if your engine has them) and ensure they are securely attached.
  • Air leaks can interfere with the air-fuel mixture, resulting in misfires. Look for cracked hoses and loose connections near the engine intake.
  • Clogged fuel injectors: Even if you used fuel injector cleaning, the injectors on cylinders 3 and 5 could be malfunctioning. A mechanic can inspect this with specialised tools.
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A Ford F-150’s P0300 code indicates that an engine misfire that occurs randomly has been found.

Your car’s misfiring cylinder problem is indicated by the P0300 engine code. When there is not enough gasoline consumed or when the spark plug is broken, misfiring occurs.

The P0300 code indicates a random or multiple cylinder misfire, which can be caused by several issues beyond spark plugs and coils. Here’s a deeper dive into possible causes and next steps:

Potential Causes:

  • Fuel Injectors: Clogged or malfunctioning fuel injectors can lead to misfires. Cleaning or replacing the injectors might be necessary.
  • Carbon Build-up: EcoBoost engines, in particular, can experience carbon build-up on the intake valves, which affects combustion. A thorough cleaning or removal of the intake manifold may be required.
  • Compression Issues: Perform a compression test to check for problems with the engine’s cylinders. Low compression can cause misfires.
  • Sensor Problems: Issues with sensors like the mass airflow sensor or oxygen sensors could be affecting engine performance and contributing to the misfire.

Next Steps:

  1. Check for Additional Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to identify if there are other codes present that could provide more clues.
  2. Inspect Fuel Injectors: Look for signs of damage or clogging. If necessary, clean or replace them.
  3. Consider Carbon Cleaning: If carbon build-up is suspected, a carbon cleaning service can help remove deposits from the intake valves.
  4. Professional Diagnosis: If the issue persists, consult with a mechanic who specializes in Ford vehicles for a thorough inspection and diagnosis.