What is this round stuff with the black tube A? A is connect to something attached to the vacuum manifold, but when I pulled A off the round thing, there is no sucking. Black tube B could not be pulled off. I am looking for a place to hook up the vacuum gauge.
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That is the EGR valve. The vacuum hose to that valve has only partial vacuum, and only at the times that the EGR valve should be open. It’s not a good place at all to check engine vacuum.
And, it’s not called a vacuum manifold. It’s the intake manifold.
I’m assuming that you mean ‘intake manifold’ instead of vacuum manifold. The round item connected to tube A should be the EGR valve, and vacuum through tube A when the engine is sped up and under load. Tube A has ‘port’ vacuum, and your looking for manifold vacuum.
I cannot tell by the photo if tube B is port vacuum or manifold vacuum. It depends on what is connected to the other end. A good source for manifold vacuum is any small tubes connected to the brake booster vacuum line. Many cars of this era had a connector that had a few small branches of vacuum line and the big brake booster vacuum line attached. Follow the brake booster line and see where it connects to the engine.