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2018 Ram 1500 Laramie - Check Engine Light P0304 and Rough Idle

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Chris P. · rep 0 · May 25, 2:26 AM · 1 replies · solved · Question

Vehicle: 2018 Ram 1500 Laramie

Hey everyone,

My 2018 Ram 1500 Laramie, with the 5.7L Hemi, just threw a check engine light. I pulled the code with my scanner, and it's showing P0304, which is a cylinder 4 misfire. The truck has about 85,000 miles on it.

It's been running a bit rough, especially at idle, and I can feel a slight hesitation when accelerating. Sometimes, the check engine light even flashes, which I know means a severe misfire. I've heard this can be a few different things, but I'm not sure where to start. Any ideas on common causes for this specific code on these Hemi engines?

I'm hoping to tackle this myself if it's something straightforward before taking it to a shop. What should I check first?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:26 AM

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ClearTheCode admin answer: A P0304 code on your 2018 Ram 1500 Laramie indicates a misfire in cylinder 4. A flashing check engine light signifies a severe misfire that could damage the catalytic converter if not addressed promptly. Here's a diagnostic approach:

  1. Check Spark Plugs and Ignition Coils:

    • Cause: Worn spark plugs or a failing ignition coil are the most common culprits for misfires. The Hemi engines are known to be sensitive to spark plug condition. Inspect the spark plug for cylinder 4 for signs of wear, fouling, or damage. Swap the ignition coil from cylinder 4 with a known good cylinder (e.g., cylinder 2) and see if the misfire code follows the coil. If it does, replace the coil.

  2. Fuel Injector Inspection:

    • Cause: A clogged or faulty fuel injector for cylinder 4 can prevent proper fuel delivery, leading to a misfire. You can test the injector's resistance with a multimeter or listen for its clicking sound with a mechanic's stethoscope. A professional can perform a fuel injector balance test.

  3. Compression Test:

    • Cause: Low compression in cylinder 4, due to issues like a faulty valve, worn piston rings, or a head gasket leak, will cause a misfire. This is less common but a critical check. Perform a dry and wet compression test on cylinder 4 and compare it to the other cylinders.

  4. Vacuum Leaks:

    • Cause: While less likely to cause a single-cylinder misfire, a significant vacuum leak near cylinder 4's intake runner could lean out that cylinder's air-fuel mixture. Inspect intake manifold gaskets and vacuum lines.

When to See a Shop: If you've checked the spark plug and coil, and potentially the fuel injector, without resolving the issue, or if the compression test reveals low compression, it's time to consult a qualified mechanic. Diagnosing internal engine issues or complex fuel system problems often requires specialized tools and expertise. Continued driving with a severe misfire can lead to costly catalytic converter damage.

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