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Rough idle and P0301 code on my 2022 Ford Mustang GT - Time for new spark plugs?

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Mike T. · rep 0 · May 25, 1:35 AM · 1 replies · solved · Question

Vehicle: 2022 Ford Mustang GT

Hello fellow Mustang owners,

I've got a 2022 Ford Mustang GT with the 5.0L Coyote engine, just hit 45,000 miles. Lately, I've noticed a rough idle, especially when the engine is cold, and sometimes a slight hesitation under acceleration. The check engine light came on yesterday, and when I scanned it, I got a P0301 code, which points to a misfire in Cylinder 1.

I haven't changed the spark plugs yet, and I know the Coyote engines can be sensitive to plug wear. Is 45,000 miles a reasonable time to start seeing misfires due to worn plugs? Could it be something else like an ignition coil or an injector? I'm leaning towards doing the plugs myself, but I want to make sure I'm on the right track.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 1:35 AM

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ClearTheCode admin answer:

A P0301 code (Cylinder 1 Misfire Detected) combined with a rough idle and hesitation on your 2022 Ford Mustang GT at 45,000 miles strongly suggests an ignition system issue, and spark plugs are a primary suspect.

Causes of P0301 & Misfires:

  1. Worn Spark Plug: The most common cause. Over time, the electrode gap widens, requiring more voltage to fire, leading to an inconsistent spark or no spark.
  2. Faulty Ignition Coil: The coil pack for Cylinder 1 could be failing, not providing enough voltage to the spark plug. This is also very common.
  3. Clogged Fuel Injector: A dirty or failing fuel injector for Cylinder 1 might not be delivering enough fuel, causing a lean misfire.
  4. Vacuum Leak: A vacuum leak near Cylinder 1 could cause a lean condition and misfire.
  5. Compression Issue (Less Common): Low compression in Cylinder 1 due to valve or piston ring issues would also cause a misfire, but typically with more severe symptoms.

Recommended Steps for Diagnosis & Repair:

  1. Swap Components: Before replacing parts, try swapping the Cylinder 1 spark plug with a plug from another cylinder (e.g., Cylinder 3). Clear the code and drive. If the misfire moves to Cylinder 3 (P0303), the spark plug is the culprit.
  2. Swap Ignition Coil: If the misfire doesn't move with the spark plug, swap the Cylinder 1 ignition coil with one from another cylinder. Clear the code. If the misfire now moves (e.g., P0303), the coil is faulty.
  3. Inspect Spark Plugs: When you remove the plugs, inspect them. Look for signs of fouling (oil, carbon), excessive wear, or damage. For your 5.0L Coyote, Ford generally recommends spark plug replacement around 60,000-100,000 miles, but performance driving or specific fuel types can shorten this. 45,000 miles is not unheard of for a plug to start failing, especially if it's an isolated issue.
  4. Fuel Injector Test: If the misfire doesn't move after swapping plugs and coils, a fuel injector could be the issue. This often requires specialized tools for testing or a professional diagnosis.
  5. Vacuum Leak Check: Listen for hissing sounds around the intake manifold and use a smoke machine or carb cleaner spray (with caution) to check for vacuum leaks.

When to See a Shop:

  • If you're uncomfortable performing the spark plug and coil swap, or if you don't have the necessary tools.
  • If the misfire persists after replacing the spark plugs and coils.
  • If you suspect a fuel injector or a more complex engine issue, as these require advanced diagnostic equipment and expertise.
  • Driving with a continuous misfire can damage your catalytic converter, so address it promptly.
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