P0301 Misfire on 2020 Eclipse Cross - Spark Plugs?

ClearTheCode admin answer:

A P0301 code on your 2020 Mitsubishi Eclipse Cross 1.5T indicates a misfire specifically on cylinder 1. While spark plugs are a common culprit, especially around 55,000 miles, it's essential to diagnose systematically to avoid unnecessary parts replacement. Here's how to approach it:

1. Swap Ignition Coil: The easiest diagnostic step is to swap the ignition coil from cylinder 1 to another cylinder (e.g., cylinder 2 or 3). Clear the code, drive the car, and re-scan. If the misfire moves to the cylinder where you moved the coil (e.g., P0302), then the coil is faulty and needs replacement.
2. Inspect Spark Plug: If the misfire doesn't move, remove the spark plug from cylinder 1. Inspect it for signs of wear, fouling (oil, carbon, or fuel deposits), or damage to the electrode. If it looks worn or fouled, replace all spark plugs with the correct OEM-specified iridium plugs. Even if only one looks bad, it's best practice to replace them as a set.
3. Check Fuel Injector: If coils and plugs are ruled out, the next suspect is the fuel injector for cylinder 1. This is harder to diagnose without specialized tools. You can sometimes listen for the injector clicking with a stethoscope or use a noid light to check for pulse, but flow testing is ideal. A clogged or faulty injector can cause a misfire.
4. Compression Test: As a last resort for a P0301, if all other components check out, a compression test on cylinder 1 can rule out internal engine issues like a bad valve or head gasket, though this is less common for a single cylinder misfire at your mileage.

Common Causes for P0301:

• Worn or Fouled Spark Plug: The most frequent cause.
• Faulty Ignition Coil: The coil provides the high voltage for the spark.
• Clogged or Failing Fuel Injector: Prevents proper fuel delivery to the cylinder.
• Vacuum Leaks: Can cause lean conditions leading to misfires, though usually affects multiple cylinders.
• Low Compression: Indicates internal engine damage.

When to See a Shop:

• If you're uncomfortable performing the diagnostic steps or replacing components.
• If the misfire persists after replacing spark plugs and coils.
• If you suspect a fuel injector issue or low compression, as these require more advanced diagnostics and tools.
• If the check engine light is flashing, which indicates a severe misfire that can damage the catalytic converter.