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2019 QX80 Luxe - Rough Idle and Misfire Codes (P030x)

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Melissa G. · rep 0 · May 22, 5:04 AM · 1 replies · solved · Question

Vehicle: 2019 Infiniti QX80 Luxe

Hey everyone,

I'm having some trouble with my 2019 Infiniti QX80 Luxe, which has about 70,000 miles. Lately, the engine has developed a really rough idle, and I can feel vibrations throughout the cabin. It's also not as smooth under acceleration as it used to be.

The check engine light came on, and when I scanned it, I got multiple misfire codes: P0301, P0303, and P0305, indicating misfires on cylinders 1, 3, and 5. This suggests a problem affecting multiple cylinders on one bank.

I'm wondering if this is a common issue with the 5.6L V8 engine in the QX80. What are the usual culprits for multiple cylinder misfires like this? Could it be spark plugs, ignition coils, or something more serious? Any advice on where to start troubleshooting would be great!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 5:04 AM

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ClearTheCode admin answer:

The multiple misfire codes (P0301, P0303, P0305) on your 2019 Infiniti QX80's 5.6L V8 engine, combined with a rough idle and vibrations, indicate a significant engine performance issue. These codes specifically point to misfires on cylinders 1, 3, and 5, which are all on the same bank of the engine (driver's side in a typical V8 layout).

Here are the most common causes for multiple misfires on one bank:

  1. Ignition System Components: While individual spark plugs or ignition coils can fail, having multiple misfires on one bank suggests a shared component. However, it's possible for several coils or plugs to degrade around the same time. Start by inspecting spark plugs for wear or fouling and checking ignition coils for cracks or signs of arcing.
  2. Fuel Delivery Issues: If multiple cylinders on one bank are misfiring, a problem with fuel delivery to that bank is highly suspect. This could include:
    • Clogged Fuel Injectors: Injectors for cylinders 1, 3, and 5 could be partially clogged or failing, leading to insufficient fuel delivery.
    • Fuel Pressure Regulator: A faulty fuel pressure regulator could be causing inconsistent fuel pressure to that bank.
    • Fuel Rail Issues: Less common, but a restriction in the fuel rail supplying that bank could cause issues.
  3. Vacuum Leaks: A significant vacuum leak affecting one side of the intake manifold could lean out the air-fuel mixture for those cylinders, causing misfires.
  4. Engine Management System (ECU) Issues: While rare, a faulty ECU or wiring harness issue affecting the control of those specific cylinders could be a cause.
  5. Exhaust System Restriction: A partially clogged catalytic converter on that bank could create excessive back pressure, hindering exhaust flow and causing misfires.

When to see a shop: Given the multiple misfire codes, it's best to have your QX80 diagnosed by a professional. They can perform a comprehensive check including fuel pressure tests, injector pulse tests, compression tests, and inspect for vacuum leaks. Driving with persistent misfires can lead to damage to the catalytic converters due to unburnt fuel entering the exhaust system.

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