2002–2009 GMC Envoy
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| Part Name | Part Number | Price | Buy |
|---|---|---|---|
| Iridium spark plugs (6, gapped 0.044 inch) | — | — | |
| Coil boots (if cracked) | — | — |
💡 Pro tip: Order all parts at once to save on shipping
Follow these steps carefully
Let the 4.2L I6 cool for at least an hour. Disconnect the negative battery terminal. Remove the plastic engine cover to expose the six coil packs in a row along the top of the valve cover — the inline-six layout gives excellent access.
Unplug each coil's electrical connector by pressing its release tab. Remove the single bolt holding each coil with a socket, then pull each coil straight up. Keep them in order from front to back. Inspect the boots for carbon tracking — the 4.2L's coils are a common misfire source.
Blow compressed air into each plug well to clear debris. Fit a 5/8-inch spark-plug socket with an extension into each well and loosen the plug. All six are accessible from the top on the inline-six — no wheel removal or contortion needed. Lift each plug out with the socket.
The 4.2L uses iridium plugs gapped to 0.044 inch — verify with a feeler gauge. Thread each plug in by hand using the extension alone until it seats, ensuring the threads start cleanly in the aluminum head. Snug with the ratchet; do not overtighten.
Push each coil firmly back onto its plug until it seats, reinstall the bolts, and reconnect the electrical connectors with a click. Reconnect the battery and replace the engine cover. Start the engine — the inline-six should idle glass-smooth. Test-drive to confirm no hesitation or misfire.
While the coils are out, check each electrical connector for green corrosion or loose pins — the 4.2L's engine bay sees a lot of heat cycling. Clean any corrosion with electrical contact cleaner. A poor coil connection causes the same misfire symptoms as a bad plug, so rule it out now.
Test your repair before closing everything up. If something doesn't work right, double-check your steps.
⚠️ Common Mistakes to Avoid
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2002–2009