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2020 Eclipse Cross SEL - Rough Idle & P0301 Misfire Code

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Angela R. · rep 0 · May 22, 5:30 AM · 1 replies · solved · Question

Vehicle: 2020 Mitsubishi Eclipse Cross SEL

My 2020 Mitsubishi Eclipse Cross SEL, with about 45,000 miles, has developed a really rough idle lately. It feels like the engine is shaking more than usual, especially when I'm stopped at a light.

I hooked up my OBD-II scanner and pulled a P0301 code, which points to a misfire in Cylinder 1. The Check Engine Light is on solid. I haven't noticed any significant power loss while driving, but the rough idle is definitely concerning.

What are the most common causes for a P0301 on these models? Should I start with spark plugs or could it be something more serious like an ignition coil or fuel injector? Any advice on troubleshooting steps would be great!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 5:30 AM

0

ClearTheCode admin answer:

A P0301 code indicates a misfire detected in Cylinder 1. This means that the engine's computer has detected that Cylinder 1 is not contributing its fair share of power to the engine's rotation. While the car might still drive, a persistent misfire can lead to reduced fuel economy, increased emissions, and potential damage to the catalytic converter if left unaddressed.

Here's a systematic approach to diagnose the P0301 code:

  1. Check Spark Plug: The easiest and often first step is to inspect the spark plug in Cylinder 1. Remove it and check for signs of wear, fouling (oil, carbon, or fuel), or damage. If it looks bad, replace it. Consider replacing all spark plugs if they are due for maintenance.
  2. Inspect Ignition Coil: The ignition coil for Cylinder 1 could be failing. You can often swap the ignition coil from Cylinder 1 with one from a different cylinder (e.g., Cylinder 2 or 3) and see if the misfire code moves to the new cylinder. If P0302 appears after swapping, the coil is likely bad.
  3. Fuel Injector Test: A clogged or faulty fuel injector for Cylinder 1 can prevent it from getting enough fuel. This is harder to diagnose without specialized tools. You can listen to the injector with a stethoscope for a clicking sound, indicating it's firing, or perform a fuel pressure balance test.
  4. Compression Test: Less common, but a loss of compression in Cylinder 1 (due to a bad valve, head gasket, or piston ring) will also cause a misfire. This requires a compression tester.
  5. Vacuum Leaks: While less likely to cause a single-cylinder misfire, a significant vacuum leak could affect engine performance and potentially trigger misfires.

When to See a Shop:

  • If you're uncomfortable performing the diagnostic steps yourself, especially with fuel system components.
  • If swapping coils or replacing spark plugs doesn't resolve the issue.
  • If you suspect a fuel injector or internal engine issue (like low compression), as these require more advanced tools and expertise.
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