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2018 Enclave Misfire, P0304 Code and Rough Idle

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Mike T. · rep 0 · May 25, 2:43 AM · 1 replies · solved · Question

Vehicle: 2018 Buick Enclave Premium

My 2018 Buick Enclave Premium with about 75,000 miles started running really rough last week. The check engine light came on, and when I scanned it with my OBD-II reader, I got a P0304 code, indicating a misfire on cylinder 4.

It's especially noticeable at idle and low speeds, making the whole car vibrate. The engine feels sluggish, and I'm worried about driving it too much like this. I've visually checked spark plug wires and coils, but nothing looks obviously damaged or disconnected.

Could this be a bad spark plug, ignition coil, or something more serious like a fuel injector? Any ideas on what I should check next before taking it to a mechanic? I'd like to narrow down the possibilities if I can.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:43 AM

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ClearTheCode admin answer: A P0304 code specifically points to a misfire in cylinder 4. This is a common diagnostic trouble code, and addressing it promptly is important to prevent further engine damage.

Here are common causes and diagnostic steps:

  1. Ignition System Components:

    • Spark Plug: A worn, fouled, or damaged spark plug in cylinder 4 is a very common culprit. It's often the first thing to check.
    • Ignition Coil: The ignition coil for cylinder 4 could be failing. You can sometimes swap the coil with an adjacent cylinder (e.g., cylinder 2) and see if the misfire code moves to the new cylinder to confirm.
    • Spark Plug Wire (if applicable): While less common on newer vehicles, a damaged wire can cause issues.

  2. Fuel System Issues:

    • Fuel Injector: A clogged, faulty, or dirty fuel injector for cylinder 4 can prevent proper fuel delivery, leading to a misfire. Fuel system cleaners might help with minor clogs, but a failing injector needs replacement.
    • Fuel Pressure: Low overall fuel pressure could cause misfires across multiple cylinders, but if it's isolated to one, the injector is more likely.

  3. Engine Mechanical Issues:

    • Compression: Low compression in cylinder 4 due to a faulty valve, worn piston rings, or a head gasket leak can cause a misfire. This requires a compression test to diagnose.
    • Vacuum Leaks: While less likely to be cylinder-specific, a significant vacuum leak could contribute to general rough running.

When to See a Shop: If you've checked the spark plug and coil for cylinder 4 and the issue persists, it's best to take your Enclave to a qualified mechanic. They have specialized tools to test fuel injectors, perform compression tests, and conduct deeper diagnostics to pinpoint the exact cause of the P0304 code efficiently and accurately. Driving with a persistent misfire can damage your catalytic converter over time.

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