Exhaust Gas RECIRCULATION: Operation

On 1974-75 models, vacuum connection on carburetor opens at throttle valve opening angle of 18 degrees. Vacuum operates EGR valve, allowing a controlled amount of exhaust gases to pass through filter, EGR valve, and into intake manifold. At full throttle, exhaust gas recirculation is eliminated as vacuum is not strong enough to keep EGR valve open.

On 1976-77 models, the EGR temperature control valve prevents vacuum from reaching EGR valve when engine is cold. When engine is warm, vacuum is supplied to EGR valve from throttle valve venturi of CIS injection system via a vacuum booster which amplifies this weak vacuum signal to a level which will operate the EGR valve. On California models, a vacuum accumulator is used to ensure an adequate supply of vacuum to vacuum booster.

On 1978-79 models, a vacuum signal is sensed by the vacuum amplifier as throttle plate opens to partial throttle. The vacuum amplifier strengthens the vacuum signal enough to allow the EGR valve to open. As the EGR valve opens, a controlled amount of exhaust gases are introduced into the intake manifold. At sustained low vacuum conditions, such as during heavy acceleration, no EGR occurs since the vacuum level is too low. However, the vacuum reservoir will maintain an operable vacuum level to accommodate fluctuations in engine operation and vacuum levels.