Would leaky return line cause nailing?
 

I installed a new injector this weekend and have been having trouble with the new return line leaking (different thread). It may be that the new injector leaks around the middle. Is this possible and would it cause nailing? The nailing started immediatly when the new injector was installed. Injector was off the shelf form MBParts.

how many miles since the replacement?

any time one of the lines is opened up these engines will knock horribly untill all the air is out. can sound quite horrific.

I have gotten bad injectors off the shelf. I wouldn't install one before testing pop pressure and spray pattern.

It has only been driven about 10 miles since the change, how long will it take to get the air out?

2 minutes.:D

So let me get this straight, you had some issue before that caused you to install a new injector. Nailing? Try swapping that injector around and see if the sound follows it.