It is important to replace the spark plugs on your Chevrolet Trailblazer every 20,000 or 30,000 miles to maintain engine performance and fuel economy. However, if you mostly drive your Trailblazer on dirt roads, at low speeds and idle the engine for extended periods, it is a good idea to check the spark plugs and the rest of the ignition system sooner. Here's how to remove and install a new set of spark plugs correctly as part of your vehicle's scheduled maintenance.
Remove the air cleaner assembly from the top of the engine to gain access to all the spark plug wires, if necessary. Pull out the first spark plug wire by twisting and pulling the wire boot. If you have a Trailblazer with a 4.2L engine, unplug the ignition coil electrical connector and unbolt the coil mounting bolt; then pull the ignition coil from the cylinder head. Work with one spark plug at a time to prevent mixing the wires or coils.
Clean the base around the spark plug of dirt and debris, if necessary. Use compressed air or a bicycle air pump. This will keep contaminants from entering the combustion chamber once you remove the spark plugs. Now unscrew the spark plug from the cylinder head using a ratchet, ratchet extension and a spark plug socket. If the spark plug seems stuck, spray the base of the spark plug with penetrating oil or silicone spray following the product's instructions.
Gap the spark plug using a wire feeler gauge. If necessary, consult the Vehicle Emissions Control Information (VECI) label or your car owner's manual for the correct gap specification for your Trailblazer model. The VECI label is in the engine compartment on the top radiator support, firewall or near the strut towers.
Install the spark plug by hand using the spark plug socket and ratchet extension. Then tighten the plug using the ratchet, but don't over-tighten it. Install the spark plug wire, making sure the wire boot snaps in place over the plug terminal. If you have a 4.2L engine model, install the ignition coil over the plug and tighten the coil mounting bolt; then plug the coil electrical connector. Remove and install the rest of the spark plugs following the same procedure. Then replace the air cleaner assembly if you had to remove it.
