vacuum plumbing question

I took apart my intake fort a new plenum gasket and have a question about vac lines. Is it true that the FP regulator hose goes to the air cleaner box just behind the secondary air cleaner?j There is a port there. I have always seen the FPR connected to a vacuum source on other engines, so this seems odd. Also there is a switching valve in that same area that appears to switch plenum vacuum to the flapper diaphragm. Makes sense, but the other side of this switch has a third shinny metal tube that appears to be the standard vac hose size. On this, I found a 1/4" piece of vacuum tubing (appears that it could have broken off a rubber vac hose). Is there a hose that is supposed to go there that is missing, or possibly a rubber cap that was broken off somewhere in it's past life. don't know what to do with this port. The fact that it is shinny metal means something was on it for most of it's life.

Appreciate the assist.

 

Yes, FPR hose is at the air box.

BTW, Under the hood is a vacuum diagram.

 

Diagram shows a round thing attached to the vacuum switch but don’t know if it is a filter or a cap

 

We don't even know what engine you have. Take a pic of the diagram and we can help you out

 

It is a 4.0. I found the part under the truck. It was a little filter of some sort and it uses the little bit of vacuum tubing as a spacer.

thanks for the effort to assist.

 

Was this the piece?

 

No, that is the Evap system filter. It is about 1" in diameter and goes on the third port of the vacuum switching valve behind the intake plenum. It switches the vacuum on/off to the plenum flapper diaphragn in the rear of the plenum. I think that I get it now. When the switch closes off the vacuum source to the diaphragm, that diaphragm needs to suck in air to release. Without the filter, it would suck in dust and debris and eventually foul the switch. Mystery cleared itself when I luckily found the part on the garage floor.