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2018 Grand Cherokee V6 Misfire and Rough Idle - P0302

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Chris P. · rep 0 · May 25, 2:21 AM · 1 replies · solved · Question

Vehicle: 2018 Jeep Grand Cherokee Limited

Hey everyone, I'm having a persistent issue with my 2018 Jeep Grand Cherokee Limited, 3.6L Pentastar. Lately, it's developed a pretty noticeable rough idle, especially when cold, and I've felt some hesitation under acceleration.

The check engine light came on, and when I scanned it, I got a P0302 code, indicating a misfire on cylinder 2. I'm wondering if this is a common issue with these engines and what steps I should take before heading to the dealer. I've heard about rocker arm issues or spark plugs, but I'm not sure where to start.

Any advice from fellow WK2 owners would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:21 AM

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ClearTheCode admin answer:

The P0302 code on your 2018 Jeep Grand Cherokee's 3.6L Pentastar engine indicates a misfire on cylinder 2. This is a relatively common issue with various potential causes. Here's a breakdown of what might be happening and what to do:

Common Causes:

  1. Spark Plugs/Ignition Coils: Worn spark plugs or a failing ignition coil for cylinder 2 are very common culprits. Over time, plugs wear out, and coils can degrade.
  2. Fuel Injector: A clogged or faulty fuel injector for cylinder 2 can lead to an insufficient fuel supply, causing a misfire.
  3. Rocker Arm/Lifter Issues: The Pentastar engine is known for potential issues with rocker arms and hydraulic lifters, which can cause valve train noise (a ticking sound) and lead to misfires if a valve isn't opening or closing properly.
  4. Compression Loss: Less common, but a loss of compression in cylinder 2 (due to valve issues, head gasket, or piston rings) can also cause a misfire.
  5. Vacuum Leaks: While less specific to a single cylinder, a significant vacuum leak could affect engine performance broadly, but usually triggers other codes.

Troubleshooting Steps:

  1. Inspect/Replace Spark Plug and Coil: Start by swapping the ignition coil from cylinder 2 with a known good cylinder (e.g., cylinder 4). Clear the code and drive. If the misfire moves to cylinder 4 (P0304), you've found a bad coil. If it stays on cylinder 2, replace the spark plug for cylinder 2. If still no change, consider replacing the coil.
  2. Check Fuel Injector: If coils and plugs don't solve it, a fuel injector test can be performed by a shop, or you can try swapping injectors (though this is more involved).
  3. Listen for Ticking: Pay close attention to any ticking noises from the engine, especially when cold. This could indicate a failing rocker arm or lifter, which is a more serious repair.
  4. Compression Test: A professional shop can perform a compression test on cylinder 2 to rule out internal engine damage.

When to See a Shop:

  • If swapping coils and plugs doesn't resolve the issue.
  • If you hear a persistent ticking noise from the engine.
  • If the misfire is accompanied by significant power loss, stalling, or other severe symptoms.
  • If you're uncomfortable performing the diagnostic steps yourself.

Addressing a misfire promptly is important to prevent potential damage to the catalytic converter from unburnt fuel.

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