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2018 Enclave V6 Rough Idle & Check Engine Light - Misfire Codes

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Mike T. · rep 0 · May 25, 2:44 AM · 1 replies · solved · Question

Vehicle: 2018 Buick Enclave Premium

Hey everyone,

My 2018 Buick Enclave Premium with the 3.6L V6 engine has developed a really rough idle lately. It feels like the engine is shaking more than usual, especially when I'm stopped at a light. The check engine light came on a couple of days ago, and it's been pretty consistent since.

I took it to AutoZone for a quick scan, and they pulled a few misfire codes, specifically P0302 and P0304. It seems like cylinders 2 and 4 are having issues. The car still drives, but there's a noticeable lack of power when accelerating.

Has anyone experienced this with their Enclave? What was the fix? I'm hoping it's not something major.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:44 AM

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ClearTheCode admin answer:

Rough idle and misfire codes (P0302, P0304) on a 2018 Buick Enclave's 3.6L V6 engine are common issues with several potential causes. Given the specific cylinders, it helps narrow down the diagnostics.

Common Causes & Diagnostic Steps:

  1. Ignition System Components:

    • Spark Plugs: Worn or fouled spark plugs are a frequent cause of misfires. The 3.6L V6 can be sensitive to plug condition.
    • Ignition Coils: A failing ignition coil for cylinder 2 or 4 would directly lead to a misfire. You can often swap coils between cylinders to see if the misfire code follows the coil.
    • Spark Plug Wires: Less common on modern engines, but still possible if damaged.

  2. Fuel System Issues:

    • Fuel Injectors: A clogged or failing fuel injector for cylinder 2 or 4 would prevent proper fuel delivery, causing a misfire. Direct Injection (DI) engines are susceptible to carbon buildup on intake valves, which can indirectly affect combustion, but a faulty injector is more direct.
    • Fuel Pressure: While less likely to cause specific cylinder misfires, overall low fuel pressure can contribute to poor combustion.

  3. Engine Mechanical Problems:

    • Low Compression: Issues like a bad valve, worn piston rings, or a blown head gasket could cause low compression in a cylinder, leading to misfires. This is usually accompanied by other symptoms like smoke or coolant loss.
    • Timing Chain: While less common for isolated misfires, severe timing chain wear or stretch can affect valve timing, leading to misfires across multiple cylinders or specific banks.

  4. Vacuum Leaks: An unmetered air leak can lean out the air/fuel mixture, causing rough idle and misfires, though it often affects more than just two cylinders.

When to See a Shop:

  • Immediately: If the misfire is severe, causing significant shaking, stalling, or a flashing check engine light (indicating active misfire that could damage the catalytic converter).
  • Soon: If you've checked basic components like spark plugs and coils and the issue persists. A professional diagnostic will involve:
    • Scanning for pending and historical codes.
    • Performing a compression test.
    • Checking fuel pressure and injector pulse.
    • Using a scope to examine ignition patterns.
    • Inspecting for vacuum leaks.
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