See if this will help with your 2004 Taurus: How-to Change the Rear Spark Plugs on a 1996 thru 2001 Ford Taurus and Mercury Sable, with 3.0L Duratec Engine
1. Remove cabin filter cowl, as if you were going to change the cabin filter.
2. Here's the trick
: Remove three 5.5 mm (7/32") screws, using a nutdriver, and remove the lower cowl. This provides plenty of room to reach the rear spark plugs. This eliminates the need to remove the upper intake manifold or work by feel. It's such an easy solution to a difficult problem!
3. TxGreaseMonkey only recommends tackling this job, if you have a 3/8-in. drive Craftsman 3-piece quick-release extension bar set or equivalent, 3/8-in. drive ratchet, 3/8-in. drive 15” flex “T” handle (breaker bar), 3/8-in. drive torque wrench (calibrated in inch-pounds), 3/8-in drive 8 mm socket, 5/8-in. spark plug socket with sponge rubber plug holder for a 3/8-in drive ratchet, silicone spray, 10” piece of 3/8-in. I.D. fuel line, Motorcraft Silicone Brake Caliper Grease and Dielectric Compound, Motorcraft SP433 platinum plugs, and a tube of Permatex Anti-Seize Lubricant (133A). High temperature nickel anti-seize compound is even better, but more expensive. Use factory-recommended plugs, since my experience using cross-referenced plugs has not been good. Make sure the engine is “stone cold” before removing any spark plugs or you increase the risk of stripping the threads in the aluminum head.
4. Silicone-spray the sponge rubber plug holder inside the spark plug socket now, so that the newly installed plug will not pull the socket off the extension bar in the spark plug tube later. You don’t need to add any more tension to the job, by losing control of anything in the deep spark plug tubes on the backside of the engine. Disconnect the electrical connector to the coil on the left rear plug. Use the 8 mm socket and ratchet to remove the hex-head bolt securing the coil. Remove coil, clean with a rag and silicone spray, and apply silicone dielectric compound, using a small screwdriver, to the inside of the spring wire going to the plug. Set the coil aside for now.
5. Connect the 6” quick-release extension bar to the spark plug socket. Insert into spark plug tube and seat over plug. Remove plug, using a 3/8-in. drive 15” flex “T” handle. A 3/8-in. drive ratchet may not provide enough leverage to remove the factory-installed plug. Proceed carefully, to prevent stripping the aluminum head.
6. Check spark plug gap and apply a half pea-size drop of anti-seize compound to the threads, making sure not to get any on the plug’s electrode or porcelain. As the plug is threaded, the compound will coat the threads. If too much anti-seize is applied, you run the risk of coking the plug in the hole, making it very difficult to remove next time. Lightly coat the outside porcelain surface of the plug with silicone dielectric grease. Install the spark plug into the spark plug tube and, using the 10” piece of 3/8-in. I.D. fuel line, thread the spark plug into the hole. Be careful not to cross-thread the plug. Connect the 6" quick-release extension bar to the spark plug socket and finish seating the plug. Attach the 3/8-in. drive torque wrench and tighten the plug to 96 in.-lbs. Use the lower end of the torque specs (7 to 14 ft.-lbs.), because anti-seize lubricant increases actual torque by around 40%. Reinstall the coil, electrical connector, and hex-head bolt. Using the same procedures, change the spark plugs on the remaining two cylinders.