Author Topic: Emission Control Two-way Valve  (Read 4231 times)


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Emission Control Two-way Valve
« on: May 22, 2009, 00:57:25 »
I am trying to replace my two-way vacuum valve and am not sure how it is supposed to be hooked up.

The emission control system on my car has been tampered with. The vacuum line from the intake manifold is directly connected to the vacuum box on the distributor. My understanding is that the vacuum line from intake manifold goes to a two-way valve, and from the two-way valve to a vacuum box on the distributor. I ordered a new two-way valve from local MB dealer. The dealer sold me a three-way valve and said the two-way valve was no longer available and this was a replacement for the two-way valve according to his parts book. The MB parts department had no idea how the three-way valve worked. He said there was an additional $3 part which I needed and he did not have.

Does anyone know how this three-way valve works and how it replaces the original two-way valve? Your help will be gratefully appreciated.

Benz Dr.

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Re: Emission Control Two-way Valve
« Reply #1 on: May 22, 2009, 04:58:43 »
The two way valve is really just a switch over valve. It's either on or off. I'm not sure how the three way valve works but I assume it has 3 or more ports because the two way only has two.

Run your line from the air control valve to the switch over valve. Vacuum always goes to the center port on the bottom of the valve. So if there are three ports on the bottom use the one in the middle. If there are two use the one in the middle. If there are two on the bottom and one on top still use the one in the middle at the bottom.
I also asume this extra 3 dollar part is a simple plug to close off the extra port that you won't need.

Plug a line in beside the middle port on the bottom of the 3 way valve and run it over to the vacuum cell on the distributor. Close off any extra open port/s on the valve and see if it works. It should. This is how the lines ran with the original switch over valve.

I use old ones from 116 sedans. I'm sure other cars have them too. You can find them under the dash. Most usually work.
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Naj ✝︎

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Re: Emission Control Two-way Valve
« Reply #2 on: May 22, 2009, 10:01:44 »
Hello, Kumar,

I just used one of these valves for an experimental application.

Check if you've got 12 V at the main valve wire with engine idling. This connects vacuum from the throttle body to the distributor. I used the top port to throttle body and the horizontal port to distributor. Leave the bottom port open so that the vacuum can vent out when the current cuts off and take away the retard. I believe its at 2400 rpm that the current should cut out from the emissions relay?


Port 2 to Throttle Body
Port 3 to distr.
Port 1 open
« Last Edit: May 22, 2009, 21:18:39 by naj »
68 280SL