Throttle Position Modified Orifice (External) EGR System (CALIF. Vehicles)

The amount of EGR is controlled by a fixed orifice, located where the EGR pipe enters the exhaust manifold. See Figure.

The orifice size varies with engine applications. The EGR valve, mounted in the crossover manifold shuts the EGR off. It is an on-off type valve and does not provide a controlled, varying amount of gas flow.

Throttle position is sensed by the VRV mounted on the injection pump throttle shaft. The valve regulates vacuum proportional to throttle travel. At wide open throttle, the vacuum switch de-energizes the solenoid, which shuts off the vacuum signal to the EGR valve. This closes the EGR valve, stopping EGR flow.