System Operation

When the engine is idling below 1300 RPM, the speed sensor on the flywheel housing monitors engine RPM and relays this information to the ECB. No EGR occurs. With the engine running between 1300 RPM and full-throttle, there are 3 possible levels of EGR.

Under light loads, maximum EGR occurs. The swing arm on the side of the injection pump uncovers both load sensors. The ECB opens all 3 electrovalves. This applies vacuum to the upper and lower chambers of the EGR valve which opens to its maximum position. Vacuum is also applied to the throttle flap vacuum motor, causing the throttle flap to close half-way.

Under medium loads, the amount of EGR becomes moderate. The swing arm covers the lower load sensor and uncovers the upper load sensor. This opens only the 2 electrovalves controlling the upper and lower chambers of the EGR valve. The throttle flap returns to a vertical or fully open position because its electrovalve is closed.

Under a high load, the amount of EGR is at a minimum. The swing arm covers the upper and lower load sensors. The only electrovalve opening is the one controlling the upper chamber of the EGR valve. This opens the EGR valve only half-way. The throttle flap remains open.

With engine under a full load, there is no EGR. The swing arm uncovers the lower load sensor and covers the upper load sensor. All 3 electrovalves are closed and the throttle flap is open.