2 What the heck does this thing do? Allows burned exhaust gases to enter the engine intake manifold.Reduces NOx emissionsWhen exhaust gases are added to the air fuel mixture, they decrease peek combustion temperatures…… For this reason, an exhaust gas recirculation system lowers amounts of NOx in exhaust.
3 What’s in an EGR system? Hmmm... A vacuum operated EGR valve. -AND- A vacuum line from the carburetorHmmm...
5 The EGR valve consists of... A vacuum diaphragmA springA plungerAn exhaust gas valveA diaphragm housing
6 What’s the valve designed to do? Control the exhaust flow into the intake manifold...SEE THE PHOTO!!!
7 Basic EGR system operation... At idle, the throttle plate in the carburetor or fuel injection throttle body is closed. This blocks off engine vacuum so it can’t act on the EGR valve. The EGR spring holds the valve shut and exhaust gases do NOT enter the intake manifold.*****If the EGR valve were open at idle, it could upset the air-fuel mixture and the engine could stall!!!*****
8 More about EGR system operation... When the throttle plate is swung open to increase speed, engine vacuum is applied to the EGR hose. Vacuum pulls the EGR diaphragm up. In turn, the diaphragm pulls the valve open.Engine exhaust can then enter the intake manifold and combustion chambers. At higher engine speeds, there is enough air flowing into the engine that the air-fuel mixture is not upset by the open EGR valve.
12 Back-pressure EGR valve Uses both engine vacuum and exhaust back pressure to control valve action.This provides more accurate control of EGR valve opening.
13 Engine coolant temperature switch Prevents exhaust gas recirculation when the engine is cold. (A cold engine doesn’t have extremely high combustion temperatures, thus, it doesn’t produce very much NOx.)Blocks the vacuum to the EGR valve below 100 degrees Fahrenheit (37.8 degrees C.) to improve the drivability and performance of the cold engine.
14 Wide open throttle valve (WOT) Sometimes connected into the vacuum line to the EGR valve.Opens under full acceleration to provide venturi vacuum to the EGR valve.At wide open throttle, intake manifold vacuum is very low, but venturi vacuum is higher.
15 Here’s two more pictures of EGR valve designs...
16 EGR jetsThe small EGR jets meter a small amount of exhaust gases into the air fuel mixture.The jets are small enough that they do not upset the idle air-fuel mixture.