What are these ?

[ChevyGuyNC]

Asking for some help from the community...

What's this electric vacuum switch? It's not the Idle A/C because that's on the other side of the carb and verified working.

There was no vacuum off it, so I bypassed it. It goes to a T that splits to carb and a canister at the front of the truck.




Then, there are these, one on each side of the engine bay. Any ideas?



..

[sick472]

I think the first pic is the TCS (Transmission Controlled Spark) solenoid...

[FirstOwner69]

Originally Posted by ChevyGuyNC

Then, there are these, one on each side of the engine bay. Any ideas

Here's some info...
http://67-72chevytrucks.com/vboard/s...d.php?t=652526

[ChevyGuyNC]

Originally Posted by sick472

I think the first pic is the TCS (Transmission Controlled Spark) solenoid...

Thanks! I'm going to keep it bypassed.

At the risk of starting an argument, From the distributor advance to manifold or ported vacuum? I've read in other threads that there was a switch from manifold to ported as a band aid to reduce emissions...

[Steeveedee]

Originally Posted by ChevyGuyNC

Thanks! I'm going to keep it bypassed.

At the risk of starting an argument, From the distributor advance to manifold or ported vacuum? I've read in other threads that there was a switch from manifold to ported as a band aid to reduce emissions...

There was a thermal switch on the thermostat housing and an electrical switch on the transmission for the TCS system. Once the engine was warm enough, the thermal switch would allow vacuum, but the switch on the transmission would not enable vacuum until in high gear (3rd for an automatic, 3rd or 4th for a manual). I think that it was also ported, but it's been a long time since I worked on those. The solenoid on the intake manifold depended on the switch on the transmission providing ground to engage and allow vacuum to the distributor. If anyone wants to argue ported/non-ported, that's on them.

[kwmech]

Early attempt at NOx control. It only allowed ported vacuum to the distributor once the engine was warmed up and the trans was in high gear. Manual transmissions got the AIR pump. Never saw tcs on a manual truck that I remember. This was in California anyways when I had my smog license a few years back. BUT it also varied by the GVW rating of the truck

[68 P.O.S.]

Originally Posted by ChevyGuyNC

At the risk of starting an argument, From the distributor advance to manifold or ported vacuum?

Avoid all the arguments and read this article by an old GM engineer. He explains everything you want to know very well. http://www.camaros.org/pdf/timing101.pdf