1978-79 Models

This system operates similar to that on the 924 models, except the placement of the thermal switch is different, resulting in slightly different vacuum flow. Below normal operating temperature, the thermal switch is closed, blocking off the vacuum path from the throttle valve housing. No recirculation occurs.

Above normal operating temperature, the thermal switch opens, and vacuum reaches the EGR valve. Acting in response to this vacuum signal, and in response to the vacuum signal received from the vacuum amplifier, the EGR valve will open, close or modulate to determine exhaust gas recirculation.

The vacuum amplifier works on two vacuum signals, one ported and one venturi, from the throttle valve housing, and in response to an exhaust gas backpressure signal. The balance of the vacuum and exhaust backpressure determine the amount of vacuum applied to the EGR valve to balance the vacuum signal from the throttle valve housing to reach full open, modulated or full closed position of the EGR valve.