The GMC Envoy was a luxury version of the GMC Jimmy from 1998 to 2000. Produced as a model of its own in 2002, the Envoy is closely related to its cousin the Chevrolet Trailblazer. The 2005 GMC Envoy was available in both two- and four-wheel drive formats. The engine choices in the 2005 Envoy were the 4.0-liter, six-cylinder with dual overhead camshafts and the 5.3-liter overhead-valve V-8. The essentials of replacing the spark plugs on either engine are the same. The only difference is the number of spark plugs and ease of access to those spark plugs.
Open the hood of the vehicle. Use a 3/8-inch drive ratchet and socket to remove the negative battery cable from the battery. Set it aside to ensure that it does not touch the negative terminal.
Remove the spark plug boot from one of the spark plugs by pulling the boot from the spark plug by hand. Do not grab the wire itself, as you risk damaging the spark plug wire. Replace the spark plugs one at a time. Remove the first spark plug, using a 3/8-inch drive ratchet and 5/8-inch spark plug socket. Attach at least a 6-inch extension between the ratchet and socket for better maneuverability in the engine compartment.
Check the spark plug gap on the new spark plug with a feeler gauge or spark plug gap tool. Locate the spark plug gap specifications for the 4.2-liter engine underneath the hood on the information placard or sticker. Look for the words "Spark Plug Gap" and set the plugs to that gap, using a spark plug gapping tool. Set the spark plug gap for the 5.3-liter V-8 at .040. Most spark plugs come already gapped at .044, so make adjustments with the gap tool.
Insert the new spark plug into the 5/8-spark plug socket. Remove the socket and extension from your ratchet. Install the new spark plug into the spark plug tube and turn the plug into the engine by hand. Do not use the ratchet to start the plug or you risk cross threading the plug.
Attach the ratchet back to the extension and tighten the spark plug until it is snug. Once snug, turn the ratchet 1/4 turn more. No torque is needed for spark plugs. Called "snug-and-a-quarter," use this method when a part needs to be tightened, but not torqued.
Reinstall the plug boot onto the new spark plug and push on the top of the boot until it clicks onto the new plug.
Repeat Steps 2 through Step 6 to complete the replacement of the remaining spark plugs. If replacing the plugs on the 5.3-liter V-8, you may need to install a 3/8-inch drive swivel attachment or U-joint adapter between the extension and the spark plug socket. The rear plugs can be difficult to access with the firewall and steering column in the way. Adding the swivel gives you greater maneuverability around these tight confines.
Replace the negative battery cable onto the battery, and tighten the cable nut down using a 3/8-inch drive ratchet and socket. Turn the tie-down nut until it is snug. No torque is needed on battery cable ends.
