Is a special tool needed?
Yes, it’s called a crow’s foot socket. They are commonly available new in the $20 range more or less. See photo.
At the Charlottesville PUB event, our member Jim Villers had his fuel injector cleaner system with him and was doing demonstrations and actual cleanings. I had my tool kit with me and we removed the injectors on several cars with it…
However, on at least one car, we could not free one of the injectors. If the injector is well stuck into the cylinder head, there’s going to be a problem. The crow’s foot socket has some “give”, so it will expand a bit. What you are hoping for is that it loosens the injector before the wrench socket expands. If it expands too much, it will slip on the hex or the socket itself will break.
While it certainly wasn’t from fuel injectors, just yesterday I was cleaning up a whole variety of old socket sets. I found a 17mm Craftsman socket that was cracked in two places! That must’ve been one heck of a bolt or nut I tried to remove. I have no recollection of breaking the socket, but it went into the trash.