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Rough Idle & Check Engine Light - 2022 Challenger R/T Scat Pack (P0304)

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Mike T. · rep 0 · May 25, 4:18 AM · 1 replies · solved · Question

Vehicle: 2022 Dodge Challenger R/T Scat Pack

I'm having some trouble with my 2022 Dodge Challenger R/T Scat Pack, which just hit 35,000 miles. Lately, it's developed a noticeable rough idle, especially when the engine is cold, and the check engine light came on. I scanned it with my OBD-II reader and got a P0304 code, which indicates a misfire on cylinder 4.

Could this be spark plugs already at 35,000 miles? I thought they lasted longer on these 6.4L Hemi engines. What's the recommended interval for spark plug replacement on the 6.4L? Any tips for diagnosing further or replacing them myself, or should I just take it straight to the dealership?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 4:18 AM

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ClearTheCode admin answer:

A P0304 code on your 2022 Dodge Challenger R/T Scat Pack (6.4L Hemi) indicates a misfire detected in cylinder #4. While 35,000 miles might seem a bit early for spark plugs on some engines, it's not unheard of for performance engines or if there's an underlying issue. The recommended spark plug change interval for the 6.4L Hemi is typically around 30,000 miles for optimal performance, so you are right in that window.

Here’s a diagnostic approach:

  1. Understand P0304: This code means the Powertrain Control Module (PCM) detected that cylinder #4 is not contributing power properly. This can be due to a lack of spark, incorrect fuel mixture, or low compression.

  2. Common Causes for P0304 (Cylinder 4 Misfire):

    • Spark Plug: Worn, fouled, or incorrectly gapped spark plug in cylinder #4.
    • Ignition Coil: A failing ignition coil pack for cylinder #4.
    • Fuel Injector: A clogged, faulty, or leaking fuel injector for cylinder #4.
    • Wiring: Damaged wiring to the spark plug, coil pack, or fuel injector for cylinder #4.
    • Compression Issue: Less common, but low compression in cylinder #4 (due to valve issues, head gasket, or piston ring problems).

  3. DIY Diagnostic Steps (Start with the easiest/cheapest):

    • Swap Spark Plugs: Since you're at the service interval, replacing all spark plugs is a good idea. If you want to confirm cylinder 4, swap the spark plug from cylinder #4 with one from a healthy cylinder (e.g., cylinder #2). Clear the code. If the misfire moves to cylinder #2 (P0302), the plug was the issue.
    • Swap Ignition Coil: Similarly, swap the ignition coil from cylinder #4 with one from a known good cylinder. Clear the code. If the misfire moves, the coil pack is faulty.
    • Inspect Wiring: Visually check the wiring harnesses and connectors for damage or corrosion leading to cylinder #4's spark plug and fuel injector.

  4. Spark Plug Replacement Tips (6.4L Hemi):

    • Tools: You'll need a spark plug socket (usually 5/8" or 16mm), a long extension, a universal joint (swivel), and a torque wrench. Ensure you have the correct OEM-specified spark plugs (e.g., NGK Iridium).
    • Procedure: Work on a cool engine. Disconnect the battery. Remove the coil pack connector and bolt, then pull out the coil pack. Use compressed air to blow out any debris around the spark plug before removal to prevent it from falling into the cylinder. Torque new plugs to spec (usually around 13 ft-lbs for these engines) to avoid overtightening or loosening.

When to See a Shop: If swapping plugs and coils doesn't resolve the issue, or if you suspect a fuel injector or compression problem, it's time to visit a qualified mechanic or the dealership. Fuel system diagnostics and compression testing require specialized tools and expertise. Driving with a persistent misfire can damage your catalytic converter.

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