The engine "miss"

Case Study #01: Solving High-Mileage Misfires (Ignition Coils & Plugs)

Status: Maintenance & Prevention
Category: Engine & Drivetrain
Author: Savvy Tech

I. The Symptoms

• The Rough Idle: The engine "shakes" or stumbles when stopped at a light.

• The Check Engine Light: Flashing or solid P0300 (Random Misfire) codes.

• Power Loss: The car feels sluggish or struggles under acceleration.

II. The Technical Diagnosis

Around 80,000 to 100,000 miles, the CTS V6 has two common failure points:

1. Coil Pack Degradation: The plastic bodies of the ignition coils crack due to heat cycles, allowing moisture and electricity to escape, causing a weak spark.

2. Plug Gapping: The factory iridium spark plugs last a long time, but the gap increases over time, requiring higher voltage and stressing the ignition system.

III. The "Savvy" Solution (Step-by-Step)

Step 1: The "Mist" Test

• Action: In a dark garage, start the engine. Use a spray bottle to lightly mist water over the ignition coils.

• Procedure: If you see tiny blue/white sparks jumping from the coils to the engine block, your coil packs are failing and need immediate replacement.

Step 2: Proper Gapping

• Action: When installing new spark plugs, use a wire-type gap gauge.

• Procedure: Set the gap to the precise factory specification (consult your owner's manual for your specific engine, usually around 0.043 inches). Do not rely on "pre-gapped" plugs.

Step 3: Anti-Seize & Dielectric Grease

• Action: Apply a thin layer of anti-seize lubricant to the spark plug threads and dielectric grease inside the coil boots.

• Why: This prevents the plugs from seizing in the aluminum head (a costly future repair) and ensures a waterproof seal for the coil packs.

Step 4: The VVT Gasket Leak

• Action: Check around the valve covers for oil leaks.

• Procedure: Oil leaking from the VVT solenoid gaskets can pool in the spark plug tubes, ruining the coil packs from the inside.

IV. Savvy Pro-Tips

• Tool Choice: Use a 5/8" spark plug socket with a rubber insert to prevent breaking the ceramic insulator when removing old plugs.

• Buy Quality: Avoid cheap coils online; stick to reputable brands like ACDelco, Denso, or Delphi for long-term reliability.