Jeep m38a1 with electrical fuel pump

[serge]

Hello

On my JEEP M38A1 (using the HURRICANE engine) I have mounted an electrical fuel pump in place of the mechanical fuel pump. Now I have a problem of noise (whistling) emitted by the end of the pipe linking the engine head to a part situated near the exhaust pipe (to collect the vapors of oil) when these late is running.

I know that these pipe is used to lead the vapors of oil from the carter to the input manifold in the aim to decrease the pollution. (system Positive Crankshaft Ventilation). What I don’t understand is the role of the mechanical fuel pump which (when used) is also connected to these pipe. It is the bottom of the mechanical fuel pump (depression side) witch is linked to these hole.

If I plug the hole showed in the picture, the engine stops!!!
Please can you explain the reason?

Regards Serge