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2018 Challenger R/T Misfire - P0304 Code & Rough Idle

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Jason D. · rep 0 · May 22, 5:37 AM · 1 replies · solved · Question

Vehicle: 2018 Dodge Challenger R/T

Hey everyone,

My 2018 Dodge Challenger R/T, with the 5.7L Hemi, has suddenly started running really rough. It feels like it's misfiring, especially at idle and under light acceleration. The check engine light came on yesterday.

I hooked up my OBD-II scanner and pulled a P0304 code, indicating a misfire in cylinder 4. I'm wondering what the most common culprits are for this specific engine and year. Should I start with spark plugs, ignition coils, or something else entirely?

Any advice on troubleshooting steps would be greatly appreciated before I take it to a shop. Thanks!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 5:37 AM

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ClearTheCode admin answer:

A P0304 code specifically points to a misfire in cylinder 4. Here's a systematic approach to diagnose and potentially resolve the issue:

  1. Inspect Spark Plug and Coil Pack:

    • Locate cylinder 4 (typically the second cylinder on the passenger side for a Hemi V8). Remove the ignition coil and then the spark plug. Look for signs of fouling, damage, or excessive wear on the plug. You can also swap the coil pack from cylinder 4 with a known good cylinder (e.g., cylinder 2) and see if the misfire code moves to the new cylinder. If it does, the coil pack is faulty.

  2. Check Fuel Injector:

    • A clogged or faulty fuel injector can also cause a misfire. You can test the injector's resistance with a multimeter or listen for its clicking sound with a stethoscope while the engine is running. If you suspect an injector, it might be worth having a professional perform a fuel pressure test and injector flow test.

  3. Vacuum Leaks:

    • Inspect vacuum lines around the intake manifold for cracks or disconnections, which can lead to a lean condition and misfires. A smoke test can effectively identify these.

  4. Compression Test:

    • If the above steps don't reveal the problem, a compression test on cylinder 4 compared to other cylinders can indicate an internal engine issue, such as a bad valve or head gasket. Low compression in cylinder 4 would be a serious concern.

When to See a Shop: If you've checked the spark plug, coil pack, and fuel injector for cylinder 4 without success, or if you find signs of low compression, it's best to take your Challenger to a qualified mechanic. They have specialized diagnostic tools to further investigate fuel delivery, engine timing, and internal engine health, which can be complex to diagnose at home.

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