[quote name='pbanders' date='May 23 2022, 07:18 AM' post='3003614']
[quote name='emerygt350' date='May 23 2022, 05:19 AM' post='3003604']
[quote name='emerygt350' date='May 23 2022, 06:05 AM' post='3003602']
[quote name='pbanders' post='3003407' date='May 22 2022, 07:18 AM']
[]. Vacuum should be connected to the 5 mm control port (the one with the thread and nut) and to the 9 mm port on the opposite end, and fresh air from the air box should be connected to the 9 mm port on the side. Most diagrams have the connections to the two 9 mm ports reversed. If you connect it that way, the valve cannot work, because there's vacuum on both sides of the internal diaphragm, and it never moves, no matter what the vacuum is in the intake plenum.
[/quote]
Just to be clear. Vacuum goes to the small port facing the passenger, that is what I have for sure. And vacuum also to the posterior port facing the rear of the car? Wouldn't that create vacuum on both sides? I don't really know what the construction of the valve looks like internally but it just feels like it would...
[/quote]
Below is a diagram of the internals of the decel valve. As you can see, it's two chambers separated by a flexible diaphragm, and a valve covering the end port.
If vacuum is applied to both the control and the side port, and the end port is connected to atmospheric pressure, the diaphragm has the same pressure on both sides and will never move, no matter what pressure is applied. This configuration is the way many of the hose diagrams show.
Now, swap the hoses on the side and end port, so that the side port is connected to atmospheric pressure and the end port to vacuum. If P1 is at atmospheric pressure and P2 is at a vacuum below the setpoint, the tension spring will hold the valve shut. Once P2 is at a high enough vacuum to overcome the spring tension, the valve opens, and P1 now cannot exceed the setpoint vacuum, limiting the vacuum - which is why the device is also called a vacuum limiter.
BTW, this is not conjecture, I have tested it in both configurations using my hand vacuum pump and hoses and tee connectors to apply vacuum to the ports. You can test it yourself, this is how it works.
[/quote]
you are correct
@pbanders i have seen hose diagrams floating around which have the wrong connections to the ports on the decel valve for 1.8 L-Jets. amongst other hose errors.
even the diagrams in the factory workshop manual covering D Jet are questionable.
often the decel valve isn't even drawn as an accurate representation with regard to ports.
you can find a reliable configuration layout in the parts catalogue.