could someone please explain to me how the egr system opens and closes. i know its function. i asked over at chevytalk.com and the guy told me that as rpm's increase, vaccum increases pulling the valve open. i thought that the vaccum decreased as rpm's increased. any help would be appreciated.

There are 2 sources for vacuum...

Manifold vacuum, which is the vacuum BELOW the throttle plates and will drop when the plates are opened...

Ported vacuum, which is a vacuum port ABOVE the throttle plates and will have an increase in vacuum as the plates are opened...

Nate the way you EGR system operayes differs based on model and year. But I can summarize like this. Manifold vac will drop dependant upon engine load. as engine load is decreased maifold vac will return. Ported Vac is above the throttle plates as stated and can never be more than manifold Vac. It is a type of timed vac. Egr valves are opened by either ported vac or a solenoid using ported or manifold Vac. and sometimes in conjunction with exhaust backpressure.

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67 prostreet BB Camaro The Combat Rat
80 z28 Camaro 355ci
71 BB SS Chevelle (clone)
2002 35th anniv SS Z28 conv.