why would someone remove the PCV valve?

[67bullet]

You guys got my curiosity up.I have a 67 truck,It has a 79 engine in it.The previous owner put the original intake manifold on it with the filler tube in it with the breather cap on it.Will this affect the overall function of the pvc system.Thanks Jeff

[RichardJ]

I didn't catch the LS1 engine in your first post. The part about pinching the vacuum source will likely have no effect, because the computer controls the rpm as well as the fuel mixture.

>>Guess I have a faulty pcv system.<<
It could be, so pull and clean the PCV Valve or replace. Be sure and check the condition of those other hoses from the valve covers.
>> but a tube from each valve cover to a Y to the pcv then to the intake.<<

I looked up some of the Catch Can installations and was surprised to find many of the installations were poorly done. Almost all, placed the Catch Can between the PCV Valve and the intake manifold (Vacuum Source). That means all the oil and crankcase fumes pass through the PCV Valve before being deposited into the Catch Can. This would leave sludge and oil in the PCV valve to hinder its operation. The Catch Can should be before the PCV to keep the crud out of the Valve as well as out of the intake manifold.

One installation actually had an open breather filter in place of the oil fill cap. This would allow crankcase fumes to spew into the engine compartment when manifold vacuum is at its lower and blow-by is highest during WOT.

A hose from the front of the throttle body, before the throttle blades is the source of fresh, filtered air to enter the pass side valve cover. This air is drawn in by the crankcase vacuum from the PCV System.
During WOT, the PCV system is overwhelmed because of low vacuum and fumes flow backwards through this hose to the throttle body and then sucked through the open throttle blades to be burned in the engine.

[RichardJ]

>>The previous owner put the original intake manifold on it with the filler tube in it with the breather cap on it.Will this affect the overall function of the pvc system<<

Much depends on what the rest of the '79 system still looks like. The '79 would have originally been a CLOSED PCV System.
Fresh air from the Air Cleaner would be plumbed to one valve cover. The other valve cover would generally hold the PCV Valve and a hose from there would connect to a vacuum source on the carb or the intake manifold.
Adding a breather cap to that system turns it into an OPEN PCV system. During WOT, crankcase fumes would still be vented into the engine compartment.

They have filler caps that don't breath. There are no open slots around the bottom edge.
Toward the end of the filler tube use, some had a collar that took a bayonet type, flat twist on cap.