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2018 Challenger R/T Scat Pack - P0304 Misfire and Rough Idle

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Heather Y. · rep 0 · May 22, 5:38 AM · 1 replies · solved · Question

Vehicle: 2018 Dodge Challenger R/T Scat Pack

Hey everyone,

My 2018 Dodge Challenger R/T Scat Pack, with about 65,000 miles, just threw a Check Engine Light. It started running really rough, especially at idle, and I can feel a definite shake through the steering wheel.

I hooked up my OBD-II scanner, and it's showing a P0304 code, which points to a misfire in cylinder 4. I've tried clearing it, but it comes right back after a few minutes of driving.

Any ideas on what could be causing this? Could it be a bad spark plug, coil pack, or something more serious like an injector? I'm hoping to tackle this myself if it's not too complex. Thanks for any advice!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 5:38 AM

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ClearTheCode admin answer:

A P0304 code indicates a misfire detected in cylinder 4. This is a common issue with several potential causes, ranging from simple fixes to more involved repairs.

Here's a breakdown of common causes and diagnostic steps:

  1. Spark Plug: A worn, fouled, or cracked spark plug in cylinder 4 is a very common culprit. Over time, plugs degrade, leading to inefficient combustion.
  2. Ignition Coil: The ignition coil for cylinder 4 might be failing. Coils provide the high voltage needed for the spark plug to fire. A failing coil will result in no spark or a weak spark.
  3. Fuel Injector: A clogged or faulty fuel injector for cylinder 4 can prevent proper fuel delivery, leading to a lean condition and misfire.
  4. Vacuum Leak: While less common for a single-cylinder misfire, a significant vacuum leak near cylinder 4 could affect its air-fuel mixture.
  5. Compression Issue: In more severe cases, low compression in cylinder 4 due to a worn piston ring, valve issue, or head gasket problem can cause a misfire.

Diagnostic Steps:

  • Swap Components: Start by swapping the ignition coil from cylinder 4 with a known good cylinder (e.g., cylinder 2). If the misfire moves to the new cylinder (e.g., P0302 appears), you've identified a bad coil. Do the same with the spark plug if the coil swap doesn't yield results.
  • Inspect Spark Plug: If you remove the spark plug, check its condition. Look for signs of fouling, oil, or excessive wear.
  • Fuel Injector Test: This often requires specialized equipment, but you can sometimes listen for the injector clicking with a stethoscope or screwdriver handle.
  • Check for Vacuum Leaks: Use a smoke machine or spray carb cleaner around the intake manifold near cylinder 4 (carefully) to see if the idle changes.

When to see a shop:

If swapping coils and plugs doesn't resolve the issue, or if you suspect a fuel injector or compression problem, it's best to take your Challenger to a qualified mechanic. They have advanced diagnostic tools to test fuel pressure, injector pulse, and cylinder compression accurately. Ignoring a persistent misfire can lead to further damage, including catalytic converter failure.

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