Tools You'll Need:
* Socket wrench set: You'll need a socket that fits your spark plugs (likely 5/8" or 13/16"). A ratchet and extensions will be helpful to reach all the plugs.
* Spark plug gap tool: To check and adjust the gap of your new spark plugs (if necessary). The correct gap is specified in your owner's manual.
* New spark plugs: Use the correct type and heat range specified in your owner's manual.
* Penetrating oil (optional): May help loosen stubborn spark plugs.
* Gloves: To protect your hands.
* Shop rags or paper towels: To keep things clean.
* Torque wrench: Essential to tighten the spark plugs to the manufacturer's recommended specification. Over-tightening can damage the threads in the cylinder head.
Steps:
1. Safety First: Disconnect the negative battery terminal.
2. Locate Spark Plugs: The spark plugs are located on top of the engine. The 1990 DeVille likely has a 4.5L V8 engine, so there will be 8 spark plugs. You'll need to consult a repair manual or diagram to precisely locate each one.
3. Access: You may need to remove parts like the air cleaner assembly, some plastic covers or possibly even some wires to access the spark plugs. Be careful and take pictures as you go to help with reassembly.
4. Remove Spark Plug Wires: Carefully pull off each spark plug wire. It's usually a good idea to mark each wire's position (e.g., using masking tape and numbers) before removal to avoid misplacing them.
5. Remove Old Spark Plugs: Use the correct socket to carefully remove each spark plug. If a plug is difficult to remove, spray some penetrating oil and let it sit for a few minutes. Avoid using excessive force; you could damage the threads in the cylinder head. Turn the socket counterclockwise.
6. Inspect Old Spark Plugs: Check the condition of the old spark plugs. They can give you clues about potential engine problems.
7. Install New Spark Plugs: Before installing the new plugs, check the gap using a spark plug gap tool and adjust if needed according to your owner's manual specifications. Gently screw the new spark plugs into the cylinder head by hand until they're snug. Then, use the socket wrench and tighten them to the correct torque specification (found in your owner's manual). Do not overtighten.
8. Reconnect Spark Plug Wires: Reconnect the spark plug wires to their corresponding spark plugs. Make sure they are securely attached.
9. Reassemble: Reinstall any components you removed to access the spark plugs.
10. Reconnect Battery: Reconnect the negative battery terminal.
11. Start the Engine: Start the engine and listen for any unusual noises.
Important Considerations:
* Repair Manual: A repair manual specific to your 1990 Cadillac DeVille is highly recommended. It will provide detailed diagrams and instructions.
* Torque Wrench: Using a torque wrench is crucial to prevent damage to the engine.
* Professional Help: If you're not comfortable performing this task yourself, it's best to take your car to a qualified mechanic.
This guide provides a general overview. Improper procedures can lead to engine damage. Always prioritize safety and consult your owner's manual or a professional mechanic if you have any doubts.
