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HOMESERVICE MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 370 (ENGINE CONTROLS - REMOVAL & INSTALLATION)IGNITION SYSTEMSSPARK PLUGSINSPECTION
2003 Chevrolet TrailBlazer 4.2 S, 4WD

Spark Plugs: Inspection

2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Inspection
WARNING: This page is about a different car, the 2003 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ensure that the correct spark plug is installed. An incorrect spark plug causes driveability conditions. Ensure that the spark plug has the correct heat range. Colder plug causes spark plug fouling. Hotter plug causes pre-ignition, causing spark plug and/or engine damage. Inspect for a bent or a broken terminal post. See Figure . Test for a loose terminal post by twisting and pulling the post. The terminal post should not move.
  2. Inspect the insulator for flashover, for carbon tracking, and for soot. These conditions are caused by the electrical charge traveling across the insulator between the terminal post and the ground. Inspect the spark plug boot for damage. Inspect the spark plug recess area of the cylinder head for moisture, such as oil, coolant, or water. A spark plug boot that is saturated causes arcing to ground.
  3. Inspect the insulator for cracks. All or part of the electrical charge may arc through the crack instead of the electrodes. Inspect for evidence of improper arcing.
    • Measure the gap between the center electrode and the side electrode terminals. An excessively wide electrode gap can prevent correct spark plug operation.
    • Inspect for the correct spark plug torque. Insufficient torque can prevent correct spark plug operation. An over torqued spark plug, causes the insulator to crack.
    • Inspect for signs of tracking that occurred near the insulator tip instead of the center electrode.
    • Inspect for a broken or worn side electrode.
    • Inspect for a broken, worn, or loose center electrode by shaking the spark plug. A rattling sound indicates internal damage. A loose center electrode reduces the spark intensity.
    • Inspect for bridged electrodes. Deposits on the electrodes reduce or eliminate the gap.
    • Inspect for worn or missing platinum pads on the electrode, if equipped.
    • Inspect for excessive fouling.
  4. Inspect the spark plug recess area of the cylinder head for debris. Dirty or damaged threads can cause the spark plug to not seat correctly during installation.
  5. Normal operation, Brown to Grayish-Tan with small amounts of White powdery deposits are normal combustion by-products from fuels with additives. Carbon fouled, dry, fluffy Black carbon, or soot is caused by rich fuel mixtures, or reduced ignition system voltage output.
  6. Excessive idling or slow speeds during light loads can keep spark plug temperatures so low that normal combustion deposits may not burn off. Oil or coolant fouling, or additives that include substances such as silicone, or very White coating, reduce the spark intensity. Most powdery deposits will not affect the spark intensity unless the substances form into a glazing over the electrode.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.