Here is some 'How To' information on replacing the ignition coils (COP - Coil Over Plug) and spark plugs on your 2003 or later year model Lincoln Navigator. This design coil is so much easier to perform maintenance on. I went to the Ford dealer and asked for a price to replace all 8 ignition coils and spark plugs, they quoted me $1,100. Which is about right. You will pay about $75 per ignition coil ($600 right there) and the rest is labor to get in and out of the vehicle. So, I went to Advanced Auto Parts and bought BWD brand ignition coils for about $42 dollars and replaced all 8. I did use Motorcraft spark plugs, thought that was a good idea. I completed the entire job in about 2.5 hours, and that was taking my time and trying to be patient. This was my first time attempting this task, but when you have a Lincoln like mine with 200K miles on it, you have time to save money. I figure I did it for about 1/3 the cost of the dealer and have a really quality job with quality parts.

Hope this helps. Please post if you have any questions or insight to add.