P0305 serious

Cylinder 5 Misfire Detected

What does P0305 mean?

The P0305 code means the vehicle's onboard diagnostic system has detected: Cylinder 5 Misfire Detected. This is a serious severity code.

Common Symptoms

  • Rough idle
  • Vibration
  • Check Engine Light
  • Loss of power

Probable Causes (Ranked by Likelihood)

  • Faulty spark plug on cylinder 5 Very High
  • Failed ignition coil on cylinder 5 High
  • Clogged fuel injector on cylinder 5 High
  • Low compression on cylinder 5 Moderate

Step-by-Step Diagnostic Procedure

  1. Swap cylinder 5 coil and plug with a known-good cylinder. Monitor which cylinder the misfire follows.

  2. Perform injector balance test on cylinder 5.

  3. Compression test if ignition and fuel components test good.

Frequently Asked Questions

The 5.4L Ford V8 has a lot of coil failures -- is P0305 likely a coil?

Yes. The Ford 4.6L and 5.4L Triton V8 engines are notorious for coil-on-plug failures, especially the original design. Aftermarket coils with an updated design are available and are the most common fix.

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