EGR System: Operation: CARBURETED

System is regulated by a dual EGR control valve located in control box. When ported vacuum is directed to control valve A, valve opens and manifold vacuum passes through vacuum chamber of control valve B. Vacuum is then bled off into air filter through a restricted orifice. This causes control valve B, as well as EGR valve to begin to open.

As control valve B opens, ported vacuum is bled off to carburetor venturi area, causing ported signal to control valve A to be reduced. This causes control valve B to close. As control valve B closes, ported signal is increased and process is repeated. Because these steps are repeated very rapidly, carburetor intake air volume and ported signal to EGR valve are proportional to engine load.

When engine is cold, vacuum signal to EGR valve is bled off to air cleaner through thermovalve A (Accord) or to atmosphere through EGR cut-off solenoid (Prelude).