Tools You'll Need:
* Socket set: Including a deep well socket that fits your spark plugs (likely a 5/8" or 13/16"). A swivel socket extension can be helpful.
* Spark plug wrench: A good quality spark plug socket is essential to avoid rounding the spark plug. A magnetic socket is extremely helpful to keep the plug from falling into the cylinder.
* Wrench(es): For various bolts and nuts you might encounter, likely including a 7/16", 1/2", and possibly others.
* Pliers: Needle-nose pliers can be useful for working with wires.
* New spark plugs: Make sure you get the correct type for your DeVille engine. Consult your owner's manual or a parts store.
* New spark plug wires: Again, ensure they are the correct ones for your vehicle.
* Protective gloves: To avoid getting grease and oil on your hands.
* Jack and jack stands: Essential for safe and proper working conditions.
* Wheel chocks: To further ensure vehicle stability.
* Shop rags or paper towels: For cleaning.
* Penetrating oil (like PB Blaster): Can help loosen stubborn bolts and wires.
* Torque wrench: Crucial for tightening the spark plugs to the correct specification; over-tightening can damage the engine.
* Safety glasses: Protect your eyes from flying debris.
Procedure:
1. Safety First: Park on a level surface, engage the parking brake, and use wheel chocks. Disconnect the negative battery terminal.
2. Access the Engine: Jack up the vehicle and securely support it with jack stands. Remove any necessary plastic undercovers or shields to access the engine compartment.
3. Locate Spark Plugs and Wires: The spark plugs are located on top of the engine. The wires connect to the spark plugs and the distributor (if equipped, some models might use coil-on-plug).
4. Remove Spark Plug Wires: Carefully disconnect the wires from the spark plugs. Take note of their order; a diagram or a picture will be helpful to ensure correct reinstallation. Sometimes you'll need to slightly pull back the wire boot to release it.
5. Remove Spark Plugs: Using the correct spark plug socket and wrench, carefully remove each spark plug one at a time. Apply penetrating oil if they are difficult to remove. If you're using a magnetic socket, keep it relatively level to prevent the spark plug from falling into the cylinder.
6. Inspect and Clean: Inspect the old spark plugs for wear and tear. Clean the spark plug well area on the engine with a shop rag or brush.
7. Install New Spark Plugs: Carefully thread the new spark plugs into the cylinder head by hand, then tighten them using the socket and wrench. Do not over-tighten. Use a torque wrench to tighten the plugs to the manufacturer's specified torque (consult your repair manual).
8. Install New Spark Plug Wires: Connect the new spark plug wires to the spark plugs and the distributor (or coil packs) in the same order as the old ones. Make sure the wires are firmly seated.
9. Reassemble: Replace any undercovers or shields that you removed.
10. Lower the Vehicle: Carefully lower the vehicle from the jack stands.
11. Reconnect the Battery: Reconnect the negative battery terminal.
12. Start the Engine: Start the engine and listen for any unusual noises or misfires.
Important Considerations:
* Coil-on-Plug (COP) Systems: Some 1999 DeVille models may have a coil-on-plug ignition system where each spark plug has its own ignition coil. The procedure will be slightly different in this case, but the general principles remain the same. You'll be removing the coil packs from the spark plugs instead of separate wires.
* Torque Specifications: Using a torque wrench and adhering to the manufacturer's recommended torque specifications is crucial to prevent damage to the engine.
* Gap Measurement: Some spark plug types require gap adjustment after installation. This is usually only necessary if you've been given used plugs that require the gap adjusted back to factory specs.
This is a complex procedure. If you are not comfortable with any step, please consult a qualified mechanic. Improperly installed spark plugs can cause serious engine damage. Always refer to your vehicle's repair manual for specific instructions and torque specifications.
