I need help identifying a part off my car... its a fitting that screws into the top of my thermostat... it has 3 vacuum ports, one of which had no hose attached to it, only some remains of a filter of some sort. The three vacuum ports are hooked up in order from top to bottom: top is hooked to a check valve that spilts to the side of the air pump and to the carb and looks to be involved with the vacuum system that holds the secondarys shut. the middle port goes to the heat riser system, and the bottom port goes to nothing, and looks to have remains of a air filter or some type of foam.

The reason I need to know about this part is because my secondaries wont unlock when the engine is warm, the vacuum thingy (technical term :rolleyes: ) holds them shut still, it unlocks when the engine is off, but not when it is running, even when it is hot.
This part seems to be connected to that vacuum system in some way, and it looks to be alot easier thing to fix than to have the carb rebuilt, so I want to check it out first.

Anyone that knows exactly how this part is supposed to function and how to test it, pls reply.




[Modified by RoyArms, 6:36 AM 11/10/2001]

 

I think this is just a temperature valve to open your heat riser. Vacuum comes from the carb, once the motor warms up, it opens up and lets the vacuum pull on the heat riser to open it up. Kind of a valve to keep the heat riser closed until it's warmed up. Your carb has a "T" and one line hooks onto this valve, the other part of the "T" goes to the canister that holds your secondaries shut. The two are not tied together. They are just both sources of vacuum. When you mash the throttle, the vacuum drops off, and the canister lets go of the secondaries so they can open. If I'm wrong on this, somebody let me know, because thats the way I always thought it should work.

 

Roy, that comes out of the top of your thermostat housing? I am assuming that is from the pace car right? I had something similar looking to that but was located in the front of the intake manifold but was part of the EGR system. One hose to the carb, another to the EGR valve and I forgette where the other went, possibaly to the heat riser. You have me stumped there pal. I am curiois about this now.
JoeB

 

Dalannex is correct. It is called a thermal vacuum switch (TVS) and by vacuum (or not) controlled by the coolant temperature at the thermosat housing it opens or closes the heater riser control valve. GM would have one.

 

ok, ya that sounds right... it just opens and closes the heat riser valve with the temperature of the water in the thermostat. I am then stumped on why the vaccum system holding the secondaries closed isnt releasing, I will post this in a new topic...

 

Is the vacuum canister that holds the secondaries shut moving? I mean, if you yank the hose off of it while the car is running, does the rod that comes out of the canister move out? If so it could be that the tension of the secondary butterflies is set too tight. That is easy to set to zero tension, so if you think it might be the problem, let me know.

 

Everybody has led you in the right direction but I just have a couple comments. The heat riser is normally open but is closed by vacuum. Once the engine warms up, that temp controlled valve will close shutting off the vacuum supply to the heat riser, which in turn allows the heat riser to open. Very important to hook the vacuum lines back up properly.

The stock manifold has one of those switches mounted to it that also goes to the EGR valve. Since some newer manifolds don't have a spot for those control valves, some thermostat housings will have two of them mounted on top.

You shouldn't have a problem finding a new valve but chances are, it's not bad. If you look on the hood of the vette, you should find an emissions routing sticker that shows where the vacuum lines should go. I don't know the exact temp the valve should open at but you can test it by heating it up while using a vacuum pump to supply the vacuum. Hook the pump up to the different ports and create a vacuum, testing to see what ports are open and closed while the switch is cold. Then heat it up in boiling water and see what happens when it's hot. Drop me an e-mail if ya need to.

As far as your secondaries, hook the vacuum pump up the the canister and create a vacuum and see if they open or not. You may just have a vacuum leak or that canister for the secondaries could be bad.

BTW, if you don't have a vacuum pump, you can by them at most parts stores for between 20 and 30 dollars.


[Modified by sharklover, 7:03 PM 11/11/2001]

 

OOPS! :eek: Sharklover is correct. The heat riser closes with vacuum and opens without vacuum. I had it backwards in my previous post. I knew better too. :bb I don't know how I got that backwards. Must have not been thinking that day. Thanks for setting me straight on that one Sharklover.

 

I inadvertantly took my EFE TVS apart (don't ask!). There is just a little valve inside that moves up & down. The bottom "connector" is just a small bleed hole to allow air in/out as the valve moves up & down.
:cheers:
Paul

 

Looks like we have that part figured out, now if we could just figure out the problem with the secondaries. :chevy