Exhaust Gas Recirculation: Description and Operation

EGR SYSTEM DESCRIPTION AND OPERATION

System Schematic:

The EGR system is designed to recirculate the exhaust gas, controlled according to the driving conditions back into the intake air-fuel mixture. It helps to slow down combustion in the cylinder and thus lower the combustion temperature which, in turn, reduces the amount of NOx emission. The amount of EGR is regulated by the EGR vacuum modulator according to the engine load.
If even one of the following conditions is fulfilled, the VSV is turned ON by a signal from the ECM. This resuits in atmospheric air acting on the EGR valve, closing the EGR valve and shutting off the exhaust gas (EGR cut-OFF).
- Engine coolant temp. below 50°C (1 22°F)
- During deceleration (throttle valve closed)
- Light engine load (amount of intake air very small)
- Engine speed over 4,800 rpm
- Manifold absolute pressure more than 120 kPa (1.2 kgf/sq.cm, 17.4 psi)