EGR System: Operation

Vacuum signal is supplied to EGR valve from a port upstream from throttle valve. When intake manifold temperature is below 86°F (30°C), vacuum signal is modulated through the orifice by an air bleed to the air cleaner (on EGR control valve orifice equipped models). Additionally, with intake manifold wall temperatures between 86°F (30°C) and 104°F (40°C), vacuum signal is further modulated through the thermo vacuum switch.

For Federal 2WD models, the vacuum signal is also modulated with atmospheric pressure through a solenoid valve that has its air flow regulated by the electronic control module. See AIR INJECTION article.

When EGR valve is open, exhaust gases flow through EGR valve and pipe and into the intake manifold. The strength of vacuum signal at EGR valve determines how much exhaust gas is recirculated.

Fig 1: Exhaust Gas Recirculation System (Calif. & Federal Models, with M/T, Including 4WD)

Fig 2: Turbo Exhaust Gas Recirculation System

Fig 3: Exhaust Gas Recirculation System (Calif. & Federal Models, with A/T, Including 4WD)