Here's how to determine the correct gap:
1. Your Owner's Manual: This is the *absolute best* source. Check your owner's manual carefully. The sticker on the car might be inaccurate or outdated.
2. Genuine GM Service Manual: A factory service manual (FSM) from GM will provide definitive specifications. These manuals are often available online or from automotive parts stores.
3. Reputable Online Resources: Websites like Haynes or Chilton often have repair manuals and specifications, but always cross-reference with the owner's manual or FSM if possible.
4. Spark Plug Packaging: The packaging of the *correct* replacement spark plugs will often specify the recommended gap.
Why the Discrepancy?
Different spark plug types (copper, platinum, iridium) can have different ideal gap specifications. An older sticker might reflect a previous spark plug type used. The 0.060" gap might be for a particularly older, less efficient spark plug design, while 0.040" may be more modern.
Do not simply choose a number. Find a reliable source to determine the precise gap for your engine and the specific spark plugs you're using. Using the incorrect gap can lead to misfires, poor fuel economy, and engine damage.
