While checking for leaks in my vacum line I discovered this (see pic). What is this and how important is it I get it fixed? Also, how will cracks in my air cleaner *** affect my idle on my carb? It appears to be the orginal OEM air cleaner ***.

 

What type of engine do you have in your truck Mr.Smitty? Mine is the 400 and in my truck those hoses are connected to the air filter case, so my guess is that's some kind of air filter.

 

That could be the ported vacuum switch for the EGR system...

 

Looks like a PCV valve...

 

The engine in a 351m/400. The part that is broken off went to where the thermostat sits inside the hose. I just wondered if it was important enough to need replacing.

 

it is a temperature controlled vacuum switch, newer than my truck, so I don't know what it controls, follow the lines
usually they are closed, to not allow vacuum until engine warms to the set value, when open vacuum "flows" through, actuating whatever is on the end of the hose

 

should be the ported vacuum switch for the egr valve.it opens at a certain temp to operate egr.

 

Well I took all of your answers and ran a seach through LMC and NPD online catalogs and discovered it is in fact a PVS. I wonder if repairing this will fix the stalling issue I have been having.... I have a feeling it was broken from the PO.

Thanks guys!! I love this site.

 

Doubt it will help your stalling, unless it's causing a vacuum leak ? Start the engine and carfully feel for vacuum around the broken fitting. Better yet you can use a can of parts cleaner and carefully spray it around all your vacuum line fittings. If the egine rpm changes then you've found a vacuum leak. Don't forget to spray it between the intake and head. The intake bolts can loosen and cause vacuum leaks too. Good luck.

 

I didnt think about spraying parts cleaner. Thanks! I'll give that a shot today. I'll go ahead and replace the PVS anyway. Im sure it was put there for a reason. I'll check the bolts as well. When I changed the oilpan gasket i could turn the bolts on it and the tran pan with my fingers. Need less to say i went over everything under there with a wrench. Might as well do the same under the hood.
Thanks DT

 

That switch is NOT a PCV valve.

It is a thermal vacuum switch, and it opens and closes certain functions based on the coolant temperature, which is why it is threaded in the thermostat housing.

The "D" in the middle port leads me to think that is where the distributor vacuum advance hooks to. Check the line and see where it goes. If I am correct, the "1" should lead to a ported vacuum source, and the "2" should lead to a manifold vacuum source.

The purpose of this switch (if it goes to the distributor vacuum advance) is to run the engine on ported vacuum ("1") under normal conditions. If the engine begins to overheat, the ported vacuum switch will deactivate "1" and switch to "2", for manifold vacuum. This will advance your timing more at idle to help cool the engine faster.

You can either replace it or remove it, but I would not leave it the way it is now because the timing advance is disabled because of the broken switch. If you remove it, you can just run a vacuum hose from the distributor to a ported vacuum source. Then plug the hole with a pipe plug.

 

PVS = Ported Vacuum Switch

The one that is pictured is a three way PVS. One end is screwed into the water jacket of the intake, and its controlled by water temp.

Port D is the port hooked up to either the main vacuum source, or the device being controlled. Depending on the application. There are numerous ones to mention. The main things are...

A: EGR valves
B: Distributor vacuum advance
C: Air Cleaner Heat Riser Doors or vacuum motors
D: Thermactor system components: Specifically the TAB valve that Bypasses air pump air from the catalytic converter to the exaust ports on the head durning cold operation.

etc...

Port 1 is open to port D when the engine is warm. (Or Cold, I forget)
Port 2 is open to port D when the engine is cold. (or warm, I forget)

EGR valves are normally controlled by two way PVS's though. Two way valves are either on or off.

You need to get one that is of the same color code. They are color coded for different temp ranges.

It also will cause drivability issues with it broke, (stalling etc...) because the PVS is hooked to either ported or manifold vacuum, or both. You have a vacuum leak with that broke. (That is if someone didn't plug it down stream already)

Good luck...

 

Thanks 81 and 85. I have one on order to be here tomorrow. 37 bucks but I have a feeling it will resolve some of the issues mentioned by you guys. The other end of the line is not plugged so this isnt working and needs to be replaced. Funny thing is the deeper I dig in to this 78 the more crap i find left behind by the PO. At last I am learning as I go. Once again guys.. Thanks!!!

 

On all the trucks around here, most of that stuff has been yarded off long long ago. Once you find and repiar all the PO's undoings, AND check for vacuum leaks, I bet it runs like a top !!!!

 

I hope so Daytona. BTW I picked up some parts cleaner today. Tmar I'll be checking for leaks.
Thanks man!!