Exhaust Gas Recirculation: Description and Operation

Fig. 57 Single Diaphragm EGR Valve Cross Section:

Fig. 58 Dual Diaphragm EGR Valve Cross Section:

PURPOSE
The Exhaust Gas Recirculation (EGR) System reduces oxides of nitrogen (NOx) produced during combustion.

OPERATION
Nitrogen combines with oxygen--forming NOx--more readily when combustion temperatures exceed 2500° F.

The EGR system reduces formation of NOx by routing exhaust gases into the intake manifold--lowering combustion temperatures up to 500° F.

- When ported vacuum reaches approximately 3 in Hg the EGR diaphragm begins to move upward--against spring tension--opening the EGR valve--mounted on the intake manifold--Fig 57--allowing exhaust gas to enter the intake manifold via exhaust crossover channels.
- As the throttle valves are opened engine speed and ported vacuum increase opening the valve further.
- The EGR valve should be fully open at approximately 7 to 8 in Hg.

At Idle - The EGR valve should be closed--The addition of exhaust gas to the air/fuel mixture at idle causes rough idling.