Hey everyone. Fairly new here but hoping you can help me out with this problem. Currently working on a late 1979 C3 Corvette.

Whilst working on it happened to break one of the TVS valves on the thermostat housing (Valve 1). Now is it essential to have this valve working or is it simply more "stuff" that can be disregarded and the hole blocked up?

I have read a little bit about EGR and EFE etc but I'm still a little confused as to whats what and where should the hoses be connected to. If you could also help clarify the purposes of the other 2 valves as well that would be great.


Here is a close up of the three valves:




And here is a shot taken a little further back to give you an overview:




Any help is appreciated


Cheers

 

Your best bet is to get a copy of the factory Chasis Service Manual and read the emissions section. Removing the equipment is more of a question of does your state have an annual emissions test?

 

I should mention I'm from Australia :p So the laws about emissions etc are different over here.

 

I have a 79 L82. I just removed the AIR pump,egr,and all
associated vacuum lines and TVS and EFE valves. I wanted to
"clean up" the engine area. It looks and also runs a little
better now. Hope this helps.

 

In 1971, GM introduced TCS (transmission-controlled spark) and the TVS (thermo vacuum switch) to meet emission control standards. TCS permits fuel economy in high gear (4th) while prohibiting vacuum advance in lower gears. Thus fuel economy was reserved for open road travel while initial start and stops supported emission control. TVS worked to return vacuum advance when it senses engine overheating had occurred, reversing the retarded spark control.


EFE (early fuel evaporation) is an additional emission system that taps the heat of exhaust gas during cold engine operation, using heat to disperse fuel droplets into fuel vapor in the combustion process. EFE consists of a silver cadmium actuator, a thermal vacuum switch and a 1/8” hose for vacuum. The actuator is located on the passenger’s side with a vacuum port, supported by a semi-flat black bracket that bolts to the backside of the exhaust manifold.

EGR (exhaust gas recirculation) operates off engine vacuum and as RPM increases, the valve opens to permit exhaust gas into the intake manifold. The effect is to reduce the exhaust temperature, complete the combustion cycle and reduce Oxides of nitrogen.

These are switches or sensors that operate off either engine vacuum or engine heat. All you are doing when you remove or leave disconnect is have a system not operable and timing is usually set for these systems when operational.

these valve are available through vendors and are not that expensive. I broke the inlet off one of mine and just used gorilla glue to reattach and still use it.

 

Cheers hunt4cleanair.

Thanks for the info. I take it then based off your info that Valve 2 is to do with the EFE as the hoses run down to the passenger side exhaust manifold and attaches to some form of actuator.

Valve 3 then would be the EGR Valve I take it.

If not please correct me :p


My theory with valve 1 is that it is involved with the vacuum advance for the distributor. So when the engine is cold it is closed hence no vacuum advance. However when the engine warms up the valve opens activating vacuum advance. In other pictures I have seen this valve is not even present and the hose runs straight from the distributor to the carby. Im thinking that the engine is from a cold climate perhaps and this was fitted to help with cold starts. I'm from Queensland Australia and the coldest it gets here is probably -2*C (29*F) on a cold day


If that is the case then perhaps Valve 1 is not even required though like you said the engine would be timed for the situation in which all systems are working.


Cheers

 

I would agree with your assessment just make sure you have no open vacuum lines. Also, go to Willcox (forum sponsor) who has the vacuum hose schematics online and reconcile what you conclude with the schematics.

http://willcoxcorvette.com/instructi..._hoses_l82.jpg

 

Does anyone know where to get the thermo switches, mine are completely shot

 

I got em from Dr. Rebuild

TVS Switch