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2018 Ram 1500 Hemi - Rough Idle & Misfire P0304

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Mike T. · rep 0 · May 25, 4:14 AM · 1 replies · solved · Question

Vehicle: 2018 Dodge Ram 1500 Laramie

Hey everyone, I've got a problem with my 2018 Ram 1500 Laramie with the 5.7L Hemi. Lately, it's been running really rough, especially at idle. The check engine light came on, and when I scanned it, I got a P0304 code, indicating a misfire on cylinder 4.

I've tried checking the spark plug and coil pack for that cylinder, but they seem okay visually. The truck sometimes feels a bit sluggish under acceleration too. Any ideas on what else I should look into before taking it to a shop? Could it be injectors or something more serious?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 4:14 AM

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ClearTheCode admin answer: A P0304 code on your 2018 Ram 1500 Laramie indicates a misfire in cylinder 4. While you've checked the basic components, there are several common causes and diagnostic steps you can take:

  1. Confirm Spark and Fuel Delivery:

    • Spark Plugs & Coil Packs: Even if they look okay, swap the coil pack from cylinder 4 with an adjacent cylinder (e.g., cylinder 2). If the misfire moves to cylinder 2 (P0302), the coil pack is faulty. If it stays on cylinder 4, the issue is elsewhere. Consider replacing all spark plugs if they haven't been done recently, especially in a Hemi.
    • Fuel Injector: A clogged or faulty fuel injector for cylinder 4 can cause a misfire. You can test this by listening to it with a stethoscope or swapping it with another cylinder to see if the misfire follows.
    • Fuel Pressure: Low fuel pressure across the rail can also cause misfires, though typically it would affect more than one cylinder.

  2. Check for Vacuum Leaks: A vacuum leak near cylinder 4 could lean out the mixture, causing a misfire. Listen for hissing sounds or use a smoke machine if available.

  3. Compression Test: A loss of compression in cylinder 4 (due to a worn piston ring, bent valve, or bad head gasket) is a more serious cause but will definitely result in a misfire. This requires a compression tester.

  4. PCV System: A clogged PCV valve or hose can sometimes lead to rough idle and misfires.

When to See a Shop: If swapping components doesn't isolate the issue, or if you suspect a fuel injector problem, vacuum leak, or low compression, it's best to take your Ram to a qualified mechanic. Continuing to drive with a persistent misfire can lead to damage to your catalytic converter due to unburnt fuel entering the exhaust. A shop has advanced diagnostic tools to pinpoint the exact cause efficiently.

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