Tools You'll Need:
* Spark plug socket: The correct size for your spark plugs (likely a 5/8" or 13/16", check your manual). This should be a deep well socket to reach the plug fully.
* Spark plug wrench: A universal joint or wobble extension will be essential to get the socket at the right angle. A magnetic spark plug socket is highly recommended to prevent dropping the plugs into the engine.
* Ratchet: A standard ratchet will work, but a flex-head ratchet can help maneuver in tight spaces.
* Extensions: You'll likely need extensions to reach the plugs. Various lengths will likely be needed.
* Gloves: To keep your hands clean.
* Shop towels or rags: To clean up any oil or debris.
* New spark plugs: Ensure you purchase the correct type and heat range for your engine. Again, your owner's manual is crucial here.
Procedure (General steps - consult your repair manual for specifics):
1. Disconnect the negative battery cable: This is crucial for safety.
2. Locate the spark plugs: On the 4.5L Northstar engine (which is unlikely for a 1990 model, but double-check your engine type!), the rear plugs are usually accessed from the top of the engine, but accessing them can be extremely difficult. Older 4.5L engines might have different access points. The repair manual is your friend here.
3. Prepare the area: Clean around the spark plug area to avoid dropping debris into the engine.
4. Remove the relevant ignition coil(s) and/or wire(s): Carefully disconnect and remove the ignition coil or wires connected to the rear spark plugs. Take pictures or make notes to ensure correct reinstallation.
5. Remove the spark plugs: Use the spark plug socket, extensions, and universal joint to carefully remove the plugs. Go slowly to avoid stripping the threads.
6. Clean the spark plug wells: Use compressed air or a brush to clean any debris from the spark plug wells.
7. Install the new spark plugs: Hand-thread the new plugs into the cylinder head, ensuring they are straight. Then tighten them using the spark plug socket and ratchet to the manufacturer's specified torque. Do not overtighten!
8. Reconnect the ignition coil(s) and/or wires: Reconnect the ignition coil or wires to the spark plugs.
9. Reconnect the negative battery cable:
10. Start the engine: Check for any misfires or unusual sounds.
Important Considerations:
* Access: This is the biggest challenge. You may need to remove parts such as the intake manifold or other components to gain access to the rear spark plugs. A repair manual is absolutely essential to guide you through this process correctly, showing the specific parts that need removal and their order.
* Torque: Use a torque wrench to tighten the spark plugs to the manufacturer's recommended torque specification. Overtightening can damage the engine.
* Safety: Always disconnect the negative battery terminal before working on the ignition system.
This is a complex task that requires mechanical aptitude and the right tools. If you're uncomfortable performing this task yourself, it's strongly recommended to take your vehicle to a qualified mechanic. Attempting this without a repair manual and the proper tools increases the risk of damaging your engine.
