Exhaust Gas Recirculation: Description and Operation

EGR System Operation:

SYSTEM DESCRIPTION
This system is used to dilute the incoming air/fuel mixture with recirculated exhaust gases. Dilution of the incoming mixture lowers the peak flame temperature in the combustion chamber and thus, limits the formation of nitrous oxides (NOx).

EGR VALVE
This is a vacuum operated valve which opens and closes a passage from the exhaust manifold to the intake manifold. Flame temperature in the combustion chamber is lowered by diluting the incoming mixture with exhaust gases. The EGR valve is controlled by the vacuum modulator and the vacuum switching valve.

VACUUM MODULATOR
This valve controls the amount of exhaust gases that are allowed into the intake manifold by sensing load conditions. EGR vacuum is controlled by monitoring exhaust manifold back-pressure and bleeding off EGR vacuum until engine load conditions are correct.

VACUUM SWITCHING VALVE
The VSV is controlled by the Electronic Control Module (ECM) and indirectly by an engine vacuum sensor. The ECU monitors the engine temperature and engine rpm and directs the VSV to control the EGR valve.