Be sure the fitting has a long neck on it. I ran into this problem when I was going to replace my valve springs. The ones in the local part stores were too short and wouldn't thread into the heads. I ended up borrowing a compression test kit and it has the right fitting for me. Beware of this, short and stubby won't work. I tried 3 different kinds until I got the right one.
Wish I had a PN or something to give you. Before tearing down your car, make sure you pop out a plug and make sure it works correctly.
Good luck....
