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2017 Chrysler 300 3.6L Rough Idle and Misfire - CEL On

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Mike T. · rep 0 · May 25, 4:21 AM · 1 replies · solved · Question

Vehicle: 2017 Chrysler 300 Limited

Hey everyone,

I'm having some issues with my 2017 Chrysler 300 Limited, which has the 3.6L Pentastar engine. Lately, it's developed a really rough idle, especially when I'm stopped at a light. It feels like the engine is shaking quite a bit.

To make matters worse, the Check Engine Light came on a couple of days ago. I had it scanned at a local auto parts store, and it pulled a P0304 code, indicating a misfire on cylinder 4. I've heard these Pentastars can have head issues, but I'm hoping it's something simpler.

Any thoughts on what could be causing this? I'm trying to figure out if it's something I can tackle myself or if it's definitely a shop visit. The car has about 85,000 miles on it.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 4:21 AM

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ClearTheCode admin answer:

A P0304 code (Cylinder 4 Misfire Detected) on your 2017 Chrysler 300 with the 3.6L Pentastar engine can stem from several common causes. While head issues are known for some early Pentastar engines, at 85,000 miles, it's worth checking simpler culprits first.

Here's a breakdown and what to do:

  1. Spark Plugs and Ignition Coils:

    • Cause: Worn spark plugs or a failing ignition coil for cylinder 4 are very common misfire causes. Spark plugs are typically due for replacement around 100,000 miles, but premature wear can occur.
    • Action: Inspect and potentially replace the spark plug for cylinder 4. You can also swap the ignition coil from cylinder 4 with a known good cylinder (e.g., cylinder 2) to see if the misfire code moves. If it does, the coil is faulty.

  2. Fuel Injector:

    • Cause: A clogged or faulty fuel injector for cylinder 4 can prevent proper fuel delivery, leading to a misfire.
    • Action: This is harder to diagnose without specialized tools. A mechanic can test fuel injector pulse and spray pattern. Sometimes, a fuel system cleaner can help with minor clogs, but a faulty injector will need replacement.

  3. Vacuum Leaks:

    • Cause: A vacuum leak near cylinder 4 or in the intake manifold can lean out the air/fuel mixture, causing a misfire.
    • Action: Visually inspect vacuum lines and the intake manifold for cracks or loose connections. A smoke test by a professional can pinpoint hard-to-find leaks.

  4. Compression Issues (Less Common, but Possible):

    • Cause: Low compression in cylinder 4 due to issues like worn piston rings, a faulty valve, or, yes, a cracked cylinder head (though less common on later Pentastar revisions).
    • Action: This requires a compression test or leak-down test, which is best performed by a qualified mechanic.

When to see a shop:

  • If swapping coils/plugs doesn't resolve the issue.
  • If you suspect a fuel injector problem.
  • If you hear unusual ticking or knocking noises from the engine.
  • If the misfire worsens significantly or causes the engine to stall.
  • If you lack the tools or confidence to perform the basic diagnostic steps yourself.

Driving with a persistent misfire can damage your catalytic converter over time due to unburnt fuel entering the exhaust, so addressing it promptly is important.

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