However, here's a general outline. Remember to consult a repair manual specific to your van's engine (the VIN plate will give you the exact engine details). This will provide diagrams and crucial torque specifications to prevent damage.
Tools You'll Need:
* Socket wrench set: You'll need sockets of various sizes, including the correct size for your spark plugs (likely 5/8" or 13/16", but check your manual). A ratchet will make this much easier.
* Spark plug socket: This is a special socket with a rubber insert to grip the spark plug without damaging the porcelain insulator.
* Extension(s) for your socket wrench: You'll likely need extensions to reach the spark plugs in the rear of the engine.
* Wrench or pliers: For removing the plug wires.
* New spark plugs: Buy the correct type and heat range for your engine (again, consult your manual).
* Gap tool (optional): To check and adjust the gap of the new spark plugs if needed.
* Gloves: To protect your hands.
* Safety glasses: To protect your eyes from debris.
* Shop rags or paper towels: To clean up any spills.
* Penetrating oil (like PB Blaster): To help loosen stuck spark plugs. Apply this *well in advance* if you suspect a difficult removal.
Steps (General - Adapt to your Specific Engine):
1. Disconnect the battery's negative terminal: This is crucial to prevent electrical shorts and injury.
2. Locate the spark plugs: They're typically on top of the engine, but their accessibility varies greatly depending on the engine. Consult your repair manual for precise location.
3. Remove the plug wires: Carefully pull off each wire, noting which wire goes to which plug. Take pictures or label them if you have trouble remembering.
4. Remove the spark plugs: Use the spark plug socket and ratchet to carefully remove each plug. Apply penetrating oil if necessary, and use gentle but firm pressure. If a plug is very difficult to remove, seek professional help to avoid damaging the threads in the cylinder head.
5. Clean the spark plug wells: Use compressed air or a shop rag to remove any dirt or debris from the spark plug wells.
6. Install the new spark plugs: Carefully screw in the new spark plugs by hand until they're snug. Then, use the spark plug socket and ratchet to tighten them to the correct torque specification (found in your repair manual). Do not overtighten!
7. Reconnect the plug wires: Attach each wire to its corresponding spark plug.
8. Reconnect the battery's negative terminal.
9. Start the engine: Listen for any misfires or unusual noises.
Important Considerations:
* Engine type: The location and access to the spark plugs will vary depending on whether you have a 4.9L inline-6, 5.0L V8, 5.8L V8, or 7.5L V8 engine. The repair manual is essential.
* Torque specification: Over-tightening spark plugs can damage the threads in the engine block, while under-tightening can cause leaks and misfires. Follow the torque spec in your manual precisely.
* Safety: Always disconnect the battery before starting any work on the ignition system.
* Difficulty: This is not a beginner's job. If you are uncomfortable with any part of this process, seek professional help. A damaged spark plug well or stripped threads can lead to costly repairs.
A repair manual specific to your 1991 Ford E-350 with its exact engine code is the absolute best resource. You can usually find these online (Haynes and Chilton are popular brands) or at auto parts stores. Use it as your primary guide throughout this process.
