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2021 CT5-V Blackwing Rough Idle and Flashing CEL - P0300

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Mike T. · rep 0 · May 25, 2:49 AM · 1 replies · solved · Question

Vehicle: 2021 Cadillac CT5-V Blackwing 6.2L Supercharged

Hey everyone,

My 2021 Cadillac CT5-V Blackwing, with the 6.2L Supercharged V8, has developed a concerning issue. It started yesterday with a rough idle, especially when cold. This morning, the Check Engine Light started flashing, and the car feels like it's misfiring pretty badly when I try to accelerate.

I managed to pull a code: P0300 - 'Random/Multiple Cylinder Misfire Detected'. No specific cylinder misfire codes yet, just the general one. I've only got about 30,000 miles on it, and I'm pretty diligent with maintenance.

Could this be something simple like bad fuel, or am I looking at something more serious like a coil pack or injector issue? I'm hesitant to drive it much with the CEL flashing. Any advice from other Blackwing owners or Cadillac experts would be greatly appreciated!

Thanks!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:49 AM

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ClearTheCode admin answer:

A flashing Check Engine Light, especially accompanied by a P0300 code and rough idle in your 2021 Cadillac CT5-V Blackwing, indicates a severe misfire condition. Driving with a flashing CEL is not recommended as it can lead to catalytic converter damage due to unburnt fuel entering the exhaust.

Common Causes of P0300:

  1. Ignition System Issues: Faulty spark plugs, worn spark plug wires (less common on modern engines), or a failing ignition coil pack for one or more cylinders. Given the random nature, it could be a failing component affecting multiple cylinders or an intermittent issue.
  2. Fuel System Problems: Clogged fuel injectors, low fuel pressure from a failing fuel pump, or contaminated fuel can cause misfires. A clogged fuel filter (if applicable) is also a possibility.
  3. Vacuum Leaks: Leaks in the intake manifold, vacuum lines, or PCV system can introduce unmetered air, leading to a lean condition and misfires.
  4. Sensor Malfunctions: A faulty Mass Air Flow (MAF) sensor, Crankshaft Position (CKP) sensor, or Camshaft Position (CMP) sensor can send incorrect data to the Engine Control Unit (ECU), disrupting fuel delivery and ignition timing.
  5. Internal Engine Issues: While less common at 30,000 miles, issues like low compression due to a worn valve, piston ring, or head gasket could cause misfires in specific cylinders.

Diagnostic Steps:

  1. Check for Specific Misfire Codes: Even with P0300, a more advanced scan tool might show pending P030X codes for specific cylinders. This is crucial for narrowing down the problem.
  2. Inspect Spark Plugs and Coils: Visually inspect spark plugs for fouling or wear. If you can identify a specific cylinder misfiring, swap its coil pack with another cylinder to see if the misfire follows the coil.
  3. Fuel Pressure Test: If no specific cylinder is identified, a fuel pressure test can rule out fuel delivery issues.
  4. Vacuum Leak Test: Use a smoke machine or listen for hissing sounds around the intake manifold and vacuum lines.
  5. Live Data Monitoring: Monitor MAF sensor readings, O2 sensor readings, and fuel trims to identify any anomalies.

When to See a Shop:

  • Immediately, if the CEL is flashing. Continued driving risks expensive catalytic converter damage.
  • If you cannot identify a specific misfiring cylinder or are uncomfortable performing detailed diagnostics.
  • If initial checks (spark plugs, coils) don't resolve the issue, as it may require specialized tools for fuel system or sensor diagnostics.

A Cadillac dealership or a reputable performance shop familiar with the Blackwing's LT4 engine can perform a comprehensive diagnosis to quickly and accurately identify the root cause of the misfires.

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