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EGR Vacuum Line...Manifold or Port?

Discussion in 'The Garage' started by 1-ton, May 13, 2006.

  1. 1-ton

    1-ton 1/2 ton status Premium Member

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    I need to reconnect my EGR, which was removed by a PO, on my 1985 K30 Duallie. I have the trucks original emissions vacuum diagram, but for some reason it shows every vacuum connection there is BUT the EGR. I am pretty sure the EGR vacuum line goes to manifold vacuum, since the recirculation is from the manifold, but I could be wrong. Does anybody else know for sure?
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    Should be run off the carb.

    http://dyeager535.topcities.com/emissions/index.html

    No heavy duty stuff there yet (Want to shoot some good photos for me to add? :)) but since the actual "on/off" for the EGR is done through a timed port in the carb, I don't see any other way for it to work right. With manifold vacuum you'd just be pulling on the valve all the time except WOT, and that's not right.

    I didn't look at the varying labels to see if the carb port used for "timing" the EGR is common throughout GM. I doubt it though.

    If you look down the primaries you MIGHT be able to see the slot for EGR to give you a clue which side it is on.
     
  3. 1-ton

    1-ton 1/2 ton status Premium Member

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    I tried to get a picture of my vacuum diagram to post, so you could copy it for your web site, but my digital camera is so crappy, that it cannot take a focused picture at close range. Man, I need a better digital camera. I looked at the diagrams you posted, and it looks like the EGR is connected to two "port" vacuum sources off the carburetor above the throttle plates. One of the sources is a "port" vacuum source off of the primary ventury, and the other "port" vacuum source off of the secondary ventury (the secondary ventury vacuum connection is probably used as a single to close the EGR, at higher RPM's), with an electronic timed/delayed vacuum solonoid in between them. I only need to connect this EGR long enough to pass smog, so I may only connect it to a port vacuum source of off the primary venturies, with a mechanical diaphragm actuated vacuum delay in between it, in order to delay the activation of the EGR, until it is past the carburetor idle circuit. Thanks for the help.
     

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