Exhaust Gas RECIRCULATION: 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 by air bleed to air cleaner. When temperature of manifold is above 104°F (40°C), signal is not modulated through an orifice on models with Auto. Trans. and 4-WD with Hitachi carburetors and modulated on all others.

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

Fig 1: Subaru Exhaust Gas Recirculation System (Exc. Auto. Trans. & 4-WD Models with Hitachi Carbs.)

Courtesy of SUBARU OF AMERICA, INC.