Replacing Your Spark Plugs and Coil Packs
This is a pretty straight-forward job on the V8 Vantage (lucky for us!). The OEM spark plugs have a service life of 70,000 miles. It's a good idea to replace your coil packs at the same time, as it isn't uncommon for them to fail at this point as well (I had an issue with mine at ~69,000 miles).
DISCLAIMER: As always, follow all safety protocols. Don't undertake this task if you aren't comfortable with it and fully understand it. You are ultimately responsible for anything you do. Neither Redpants, LLC or myself is responsible or liable for anything that may occur.
Before you begin: The trick I use to reach all eight spark plugs without having to move anything out of the way is to connect a wobble joint between the spark plug socket and extension. If you don't have a lock on the wobble socket or extension, use a couple loops of electrical tape to keep them from disconnecting. It should look like this:
Disconnect your battery!!
Remove the covers from on top of spark plugs. They pull right off. Be careful as you remove these as they're plastic and the pegs underneath can break easily.
Disconnect the coil packs.
Use the T20 Torx bit to loosen the bolt holding one of the front coil packs. Pull the coil pack out, making sure not to drop the small spacer between the coil pack and the engine. Remove the next coil pack and continue until all four on that side are out. Repeat for the other side of the engine.
Use the spark plug socket, wobble socket, extension, and ratchet to remove the first spark plug. Once removed, install the new spark plug. Torque to the spark plug manufacturer's specifications. The OEM spark plugs are made by NGK and they specify 18-20 Nm.
Repeat for the next spark plug and continue until you've replaced all eight spark plugs.
Make sure you have the spacer on the coil pack's bolt.
Install the coil pack in one of the rear-most positions. Once done, install the next-closest one, and repeat until you reach the front of the engine. Repeat for the other side, again starting in the rear of the engine.
Reconnect all eight coil packs, then reconnect your battery. Start the car to make sure everything works, then put the covers back on the engine.