1. Preparation:
* Safety First: Disconnect the negative terminal from your battery. This prevents accidental shorts and shocks.
* Gather Tools: You'll need a spark plug socket (likely a 5/8" or 13/16" depending on your engine, double-check your owner's manual), a ratchet, extension(s) (likely several to reach the rear plugs), a spark plug gap tool (to check the gap on new plugs if needed), new spark plugs (make sure they're the correct type for your engine – consult your owner's manual), and a wire brush or compressed air to clean the area. A swivel socket or universal joint can be VERY helpful. Gloves are also recommended.
* Consult a Repair Manual: A Haynes or Chilton repair manual specific to your 1991 Chevy Lumina V6 is highly recommended. It will provide detailed diagrams and instructions tailored to your vehicle.
2. Accessing the Rear Spark Plugs:
This is the most challenging part. The process usually involves:
* Removing Intake Manifold Components: This is *likely* necessary. You might need to remove the upper intake manifold or at least some parts of it to get adequate access to the rear plugs. This will involve disconnecting various vacuum lines and possibly even fuel injectors (if the fuel rail is in the way). Be meticulous in noting where everything goes to ensure correct reassembly.
* Working Around Other Components: You'll likely be working around the engine's firewall, other engine components, and potentially the AC lines. Be extremely careful not to damage anything.
* Using Extensions and a Swivel: The extensions and possibly a universal joint are crucial here to navigate the tight spaces. You may have to use a combination of extensions and angles to get the spark plug socket properly positioned.
3. Removing and Replacing the Spark Plugs:
* Clean the Area: Use compressed air or a wire brush to clean the area around the spark plugs before you start working on them to prevent debris from falling into the cylinder.
* Remove the Spark Plug Wires: Carefully disconnect the spark plug wires one at a time. Note which wire goes to which plug so you can re-connect them correctly. Some people mark them with tape or take a picture.
* Remove the Spark Plugs: Use your spark plug socket and ratchet to carefully remove the spark plugs. Avoid cross-threading.
* Install the New Spark Plugs: Install the new spark plugs by hand, tightening them just snug. Then, use your ratchet to tighten them to the manufacturer's specified torque (check your repair manual). Over-tightening can damage the plugs or the threads in the cylinder head.
* Reconnect the Spark Plug Wires: Reconnect the spark plug wires in the correct order.
* Reassemble: Carefully reinstall any components you removed (intake manifold parts, etc.).
4. Final Steps:
* Reconnect the Battery: Reconnect the negative battery terminal.
* Double-Check: Inspect your work to make sure everything is properly reassembled.
* Start the Engine: Start your engine and listen for any unusual noises.
Important Considerations:
* If you're not comfortable with this level of automotive repair, take your vehicle to a qualified mechanic. Improperly installing spark plugs can lead to engine damage.
* The 1991 Lumina V6 engine bay is relatively cramped. This job is significantly more challenging than working on the front three plugs.
* Take lots of pictures as you disassemble things so you can easily reassemble correctly.
Remember to always consult your repair manual for specific torque specifications and detailed instructions. This is a complex job and attempting it without the proper knowledge and tools can cause significant damage.
