Need help to identify hose at throttle body

[aguntert]

Hi there!

My car is a 1980 SC (ROW), i.e. no lambda. Just bought the car and still going through it. While working on the engine I noticed a hose that had one open end disconnected and was just coiled and left there. But the other end is connected to the throttle body. I would assume this hose should be connected to somewhere? Please refer to the attached picture. Could you please help me to identify this hose and where it should be connected to? My distribuitor has only one vacuum connection and that is connected to the throttle body (just above the hose that is currently going nowhere).

Many thanks!!

[PeteKz]

The vacuum hose to your distributor should be connected at the front of the throttle body (towards the front of the car).

Have you checked that the vacuum advance on your distributor is working correctly?

Where is the other end of the hose connected to your Warmup Regulator (WUR)?

[john walker's workshop]

Looks like the vacuum retard hose, but being you have a single vacuum distributor, it's not used. If it has vacuum at idle, that's what it is.

[aguntert]

Originally Posted by john walker's workshop

Looks like the vacuum retard hose, but being you have a single vacuum distributor, it's not used. If it has vacuum at idle, that's what it is.

Thanks John. I will do the test. Since my dizzy is single vacuum, I suppose I can just blind this hose off?

[PeteKz]

The top nipple on the back of the throttle body goes into the throat ABOVE the throttle plate, so it should have almost no vacuum.

The lower nipple goes to a small hole just below the throttle plate, IIRC. It provides "port vacuum" which should go to the retard side of the vacuum advance can. Since your distributor does not have a can with both vacuum retard and vacuum advance, it should be blocked off. Go to your FLAPS and get some vacuum plugs and cover the nipple.

Again, check that your distributor vacuum advance is working correctly. Based on your description of where the hoses go, I don't think it is correctly connected.

[AndrewCologne]

Almost, ...

regarding to the Porsche parts catalogue graphic shown below ...

- yes, the upper vacuum (below in red) connection on the front is a venturi for the Ambient air pressure
- but the lower connection (green) on the front is not ported vacuum but the manifold absolute vacuum, or known as manifold absolute pressure, if seen form the ambient pressure measuring side. Here the more load is present the less vacuum is the result so by this the vacuum in the WUR drops and so the control pressure drops as well. With more vacuum here on this conduct the deceleration valve opens for among other things avoiding pops and plows in the exhaust flow.
- the connection at the back side (blue) is actually the ported vacuum only present at low load (higher vacuum at light opened throttle) when driving

Originally Posted by aguntert

My distribuitor has only one vacuum connection and that is connected to the throttle body (just above the hose that is currently going nowhere).

Your hose is not connected correctly, the one to the distributor must be connected to the connector at the back of the throttle body. See graphic.

[aguntert]

Hi guys,

Many thanks for taking the time to help me out here. I believe I solved my own problem: Looking at your responses and reviewing the factory manual vaccum diagram for 79 model, my loose hose was originally connected to the diverter valve of the air injection system (smog pump) that previous owner has removed (and apparently forgot to blind off the vacuum line).

AndrewCologne: Your site has been super helpful. Vielen Dank!