Exhaust Gas Recirculation System - Description and Operation
Exhaust Gas Recirculation: Description and Operation
The EGR system returns a small metered amount of engine exhaust gases to the intake manifold where it is mixed with incoming air and fuel. This
air/fuel/exhaust mixture lowers the combustion temperature, which reduces the formation of oxides of nitrogen (NOx).
Exhaust gas recirculation is controlled by an EGR control valve. The EGR control valve is installed "in line" in a passage between the exhaust
manifold and the intake manifold. Earlier models use external tubes to route exhaust gasses from the exhaust manifold, through the EGR valve,
and into the intake manifold, while on later model engines, the gasses are routed through internal passages in the cylinder head. The EGR valve is
controlled by a ported vacuum signal, taken from the carburetor. This vacuum signal is modified depending on the vehicle, to control the amount
and timing of exhaust gas recirculation.
76-82 Exc R17, 80-82 R5, 82 Fuego
This EGR system consists of a typical EGR control valve, operated by a vacuum signal which is modified, depending on engine operating
conditions. A thermal vacuum valve blocks the vacuum signal to the EGR control valve when coolant temperature is below 113 F.
Fig.10 - Exhaust Gas Recirculation System
A vacuum solenoid switch (18), controlled by a switch on the transmission (19), Fig. 10, Mocks the vacuum signal to the EGR control valve when
the transmission is in high gear on 1976-78 R5 & R18 models, and when the transmission is in neutral on 1979 R5 models. A Vacuum amplifier is
used on R5 models.
The EGR valve is controlled by a ported vacuum signal, except on models where a vacuum amplifier is used. On these models, the vacuum
amplifier (22), Fig. 10, is controlled by the ported vacuum signal, and applies a stronger, manifold vacuum signal to the EGR control valve. Both
the thermal vacuum valve and solenoid valve modify the actual EGR valve signal.
