1985 300TDT
The switchover valve on my car was bypassed when I purchased it. I want to replace the valve and put the car back to factory. I have viewed several vacuum diagrams for the 1985 and several hundred posts. My questions are: what is the CORRECT way to hook up the valve? Most diagrams show the line from the manifold hooks to the bottom port of the valve and the line from the ALDA goes to the side port near the top of the valve. The very top port is the vent. I have seen several pictures on this forum as well as other forums that have these lines reversed; i.e. manifold to the top side port and ALDA to the bottom port. Does it matter and if so, what are the correct connections?
Thanks
John

You can verify the proper connections by actuating the valve. The line from the manifold should be "blocked,"; the line to the ALDA should be vented to the atmosphere. With the valve not actuated, the lines should be connected to each other but not to the vent.

The attachment may help.

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83 SD

84 CD

It doesnae matter. Do what is most convenient.

Considering the manner in which the valve operates, how is it even remotely possible that "it doesnae matter?"

Connected incorrectly, the valve will operate completely opposite from what is intended.

One port should be open in either position; that port needs to connect to the ALDA. In the non-actuated position, one port is connected to the aforementioned port; that needs to be connected to manifold pressure. The remaining port is the vent; it should be blocked when the valve is not actuated and connected to the ALDA port when actuated.

http://www.peachparts.com/shopforum/2979497-post2.html

If you look at the above diagram from another post...it clearly shows the line from the back of the manifold going to the bottom of the switchover valve #126 and the line coming off the side of the valve going to the ALDA. Top is a vent.

If you look at this post:
http://www.peachparts.com/shopforum/3008785-post2.html

It shows the same switchover valve but the line from the ALDA is going to the bottom of the valve and the side port going over to the manifold{although that part of the picture is hidden} Top port is open as a vent.
The poster shows this picture as the correct position after he had it hooked up according to the diagram{wrong according to him}

I suppose I could just switch them around and see what happens but I'm thinking the first post diagram is correct and the second post has it backwards??

Here is a picture of the switchover bypassed on my firewall. The top is a vent with no hose going to it, just a cap. The switchover #125 in the diagram shows a hose so it has to be #126 in the diagram.
Am I overthinking this or what?!

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Just hook it up; it does not matter which way. If you have virtually no power, it is wrong. Switch the hoses. Simple. I had the original 1981 switchover valve and the replacement is not exactly the same. I could hardly get over 30mph after I put the new one in. Switched the lines and bingo, power again. You are not going to hurt anything. Just hook it up.

If you exclude the vent, you will have good power regardless of how the two lines are connected. But you can still have the lines backwards with respect to how they need to be configured when the valve is actuated; the wrong line will be vented.

Did you ever get it resolved? Think I found a pic of my new switchover valve which shows the vac lines and the top connector open.

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I got it resolved. New Pierburg switchover valve and new banjo/hard lines from intake to valve and ALDA to valve. The intake line was cracked so I just replaced both with the valve. Intake line goes to bottom of valve. ALDA line goes to side port on top and very top port is the vent. Car has much more power{ I think the power increase is more because of the cracked line replacement than the valve}

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1985 300TDT
2013 E350 Bluetec

Yes, that is just how mine looks. Glad you got it fixed.