What do you mean by knocking?

When the engine is running that patter patter patter is just valve clatter and is normal.

However in the case of some mistake or bad parts in the injection process can cause a small pinging that rides underneath of the clatter.

Break off the injector hard lines one by one to determine what cylinder is causing the pinging. From there find out where the problem is.

__________________
-Typos courtesy of my mobile phone.