Can anyone tell me what the thermal vacuum switch in the waterneck is used for?
The only other TVS was in the intake manifold for the EFE...

 

What model? What engine? What year? What emissions package? My old G20 van had 2 TVS on it. One for the emissions vacuum advance/canister purge and EGR and the other for the EFE and trans lockup.

 

There are some carb v8 vacuum diagrams here

https://www.thirdgen.org/forums/tech...iagrams-i.html

 

My car is a '83 Firebird but it has a 350 now with '84 L-69 intake, exhaust, and all accessories. So for all practical purposes, we're talking about a '84 Z-28 L-69 with the ECM removed. I still want to run the vapor canister.

On another note; the Canadian diagram shows the distributor vacuum advance connected to a TVS. Is there some reason I would want the vacuum advance not to function when the engine is cold??...

 

One of them is for vapor canister purge (has about 3/8" hose nipples); the other is the EFE TVS (much smaller hoses). The purge doesn't occur until the engine warms up.

Always remember, A GREAT DEAL of that stuff has NOTHING WHATSOEVER to do with how well the engine runs, what you or I want, etc. It's all about EMISSIONS. There may have been some random reason that somebody thought some emission or other would be lower with that "accessory". I know of no compelling necessity for it, in any other context.

 

I was just wondering if the TVSs could be differentiated by their location (waterneck, intake manifold coolant port, etc). I figured out which one is for the EFE (now eliminated) because it's normally open. So in this case, that leaves only one other TVS (in the waterneck). I'm assuming it's for the vapor canister purge. The EGR was originally run by a solenoid connected to the ECM which would apply or cut off vacuum as necessary. The other fitting in the waterneck was the temperature sensor for the ECM (also now removed). I know the later thirdgens are different, so just hoping that some '83-'85 L-69 owners can give me some pointers. This forum has already been a big help...

 

My 83 had both the TVS and an EGR Bleed solenoid for the EGR.

 

So I discovered that I was wrong about which TVS was which.
Turns out the one in the intake manifold (1/4" hose fittings) is the one for the canister control valve, and it is bad because it's open all the time. The other TVS in the waterneck (3/16" hose fittings) was for the EFE and the AIR.
All the new replacements for the CCV I see have an opening temp of 130 degrees, not 170....