I just bought a new ported vacuum switch for my EGR valve, and it has two ports. The top port is marked "E" and the bottom port is marked "S". Which port does the EGR valve hook to, and which port is for the ported vacuum source?

 

Does it look like this?








If so, I don't think it'd matter which vacuum line is connected to which port as it's only a 2-port valve.

 

I agree with the above, it shouldn't matter but for reference the vacuum diagram for a factory Holley 4180 equipped vehicle will have an "S" for the ported vacuum advance source on the carb and "E" for the EGR port on the carb. (Both ports are essentially "ported" but I hooked a vacuum gauge to the EGR port on a 4180 and it only pulled 5" of vacuum off idle, while the ported source matched full manifold vacuum off idle).

 

YES, that is exactly what is looks like. And the vacuum lines can go to either port?

The problem is, my replacement carburetor doesn't have a separate "E" port for the EGR like my stock carburetor had. I was going to just tee it in to the "S" port on the carburetor, which is the same port the vacuum advance goes to. Will that be ok?

 

You need a "ported" vacuum source... this will NOT supply vacuum at idle.

All carburetors to my knowledge have that somewhere.

 

What carburetor do you have on there now?

If it's a Holley or an Edelbrock all the installation manuals are available online at the manufacturers website's.

 

FYI. on the 2-port valves, "S" is signal or spark, "E" is EGR valve. When the valve is closed the "E" port is vented internally so that there is no possibility of having vacuum on the EGR valve. Once the operating temperature is reached, "S" and "E" are connected. If you reverse the ports, you will have a vacuum leak at low temperatures.

 

If you guys will recall, I re-did the EGR on my 83, but it has 3 connectors. Thinking of fixing my 80 (it's not connected at all), it has 2 like the pic. Good info here, I'll just nab the lines off of my 83, fix it in 5 minutes. Truck is running good, fuel mileage is kinda poor.

 

Yes, be careful, a lot of times it does matter. As he mentioned, the output port on many of these valves is vented to the atmosphere when the valve is shut, to release any vacuum on the device so the device will de-activate.