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2020 Navigator Rough Idle & Misfire - Check Engine Light On

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Mike T. · rep 0 · May 25, 4:28 AM · 1 replies · solved · Question

Vehicle: 2020 Lincoln Navigator Reserve 3.5L EcoBoost

My 2020 Lincoln Navigator Reserve, with the 3.5L EcoBoost engine, has developed a really rough idle recently. It feels like the engine is shaking more than usual when I'm stopped at a light.

The check engine light came on a couple of days ago, and I had it scanned. It's showing a P0304 code, indicating a misfire in cylinder 4.

I haven't noticed any significant power loss while driving, but the rough idle is definitely concerning. What could be causing this, and is it something I can easily fix myself?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 4:28 AM

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ClearTheCode admin answer: A P0304 code on your 2020 Lincoln Navigator indicates a misfire specifically in cylinder #4. This means that cylinder is not contributing to the engine's power output as it should, leading to the rough idle you're experiencing.

Common Causes for a Misfire (P030X):

  1. Faulty Spark Plug: Worn, fouled, or incorrectly gapped spark plugs are a very common cause of misfires.
  2. Bad Ignition Coil: The ignition coil provides the high voltage for the spark plug. If it's failing, the spark plug won't fire correctly.
  3. Clogged Fuel Injector: A fuel injector that isn't delivering enough fuel, or is stuck open/closed, will cause a misfire.
  4. Vacuum Leak: An air leak in the intake manifold or vacuum lines can lean out the air/fuel mixture in one or more cylinders.
  5. Low Compression: Less common, but internal engine issues like worn piston rings or a bad valve can cause low compression and a misfire.
  6. Wiring Issues: Damaged wiring to the ignition coil or fuel injector can prevent proper operation.

Diagnostics:

  • OBD-II Code: P0304 specifically points to cylinder 4.
  • Swap Test: A common diagnostic step is to swap the spark plug and/or ignition coil from cylinder 4 with a known good cylinder (e.g., cylinder 1). If the misfire code moves to the new cylinder, the swapped component is faulty.
  • Fuel Pressure Test: To rule out fuel system issues.
  • Compression Test: If other tests are inconclusive, a compression test can check the mechanical integrity of the cylinder.

When to See a Shop: While a spark plug or ignition coil replacement can be a DIY fix for some, accessing cylinder 4 on a 3.5L EcoBoost can sometimes be challenging, especially if it's located under the intake manifold. If you're not comfortable with automotive repairs, or if swapping components doesn't resolve the issue, it's best to take your Navigator to a trusted mechanic. Prolonged driving with a misfire can damage the catalytic converter due to unburnt fuel entering the exhaust system.

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