Exhaust Gas RECIRCULATION: Operation
A vacuum signal is supplied to the EGR valve from a port upstream from the throttle valve. When intake manifold temperature is below 86° F (30° C), the vacuum signal is modulated by an air bleed to the air cleaner. When temperature of the manifold is above 104° F (40° C), the signal is modulated through an orifice on 2-WD Man. Trans. models, and not modulated on 4-WD and Auto. Trans. models.
When the EGR valve is open, exhaust gases flow through the EGR pipe through the valve and into the intake manifold. The strength of the vacuum signal at the EGR valve determines how much exhaust gas is recirculated.