Ported Vacuum Switch question

TDubya · Jul 22, 2019

Years ago when I upgraded to a 4 bbl carb, I also removed most of the emissions plumbing. One of the items that I did not remove was the cooling ported vacuum switch (PVS) in the thermostat housing. The vacuum lines were removed and capped, but it also had electrical connections going to it. I am not having any issues and understand what the purpose of the PVS was, but am curious about the electrical connections.

Ovalis · Jul 22, 2019

It's been awhile since I brushed up on all this emissions stuff, but the electrical portion of that switch was tied to the solenoid valve that was connected to the bypass-dump valve for the Thermactor air pump. It was supposed to bypass the air going to the exhaust manifold when the temp was over 220 to protect the catalytic convertor. The thing that puzzles me is I believe that switch was 1975 only, so not sure how they accomplished that in later years or possibly they did away with that process because they felt it wasn't necessary.

jckkys · Jul 22, 2019

The PVSs control the EGR valve. If you can legally remove the EGR, you can also remove the PVSs and the solenoid wired to the electric thermostatic switch.

jckkys · Jul 22, 2019

Ovalis is correct some of the switches effect the Thermactor crap. That why I bought a '68 and put the frame and glove box door in my '77. Now all I need is PCV. It's not a cheap fix but it is 100 percent legal.

Ovalis · Jul 23, 2019

There were a few PVS's through the years. The one that controls the EGR is the 2 port PVS that is screwed into the coolant elbow in the manifold going to the heater core. The one TDubya is refering to is the 3 port PVS that is screwed into the thermostat housing that switches between ported vacuum & manifold vacuum to the vacuum advance on the distributor. I think they started using that one around 1970-71, but in 1975 (i think that was the only year) that same PVS had an electrical switch on top of it.

TDubya · Jul 23, 2019

Thanks for the replies. Just trying to clean up the engine compartment and get rid of some dead wiring. Since all of the stock emissions stuff is off, I didn't think the wiring to the PVS did anything anymore. Going to replace the PVS with a plug and remove the wiring which goes into the stock harness. Thanks

Ported Vacuum Switch question

TDubya

Sr. Member

Ovalis

Full Member

jckkys

Bronco Guru