Equus 3660 - Hand Vacuum Pump & Brake Bleeding Kit - Manual (Page 13)

3660 11
Depending on the make, model and year of your vehicle, the EGR valve
may be controlled by one of two methods (see Figure 5):
• Ported Vacuum - The EGR valve is actuated by ported vacuum
from above the carburetor's throttle plates. The amount of exhaust
gas that is recirculated back into the combustion chamber depends
on the amount of vacuum that reaches the EGR valve. At idle and
at wide open throttle a negligible amount of vacuum reaches the
valve and the valve stays closed. As the throttle plates gradually
open, vacuum reaches the valve and the valve starts to open. A low
vacuum to the EGR valve will cause the valve to open slightly. As
the vacuum to the valve increases, the EGR valve continues to
open until it is fully opened.
• EGR Control System - The control system monitors engine
operation and modulates the amount of EGR based on engine
operating conditions such as coolant temperature, ambient air
temperature, exhaust back pressure and engine speed or load.
To improve drivability before the engine has reached normal operating
temperature, most vehicles use a thermal switching device, which
shuts off the EGR system while the engine is cold.
VACUUM
PORT
DIAPHRAGM
ACTUATING ROD
SPRING
SEALED
HOUSING
THROTTLE
PLATE
EXAUST
FLOW
EGR
FLOW
INTAKE
FLOW
Figure 5. Typical EGR System Operation