320 Auto Engine Repair Copyright by Goodheart-Willcox Co., Inc. Exhaust gas in Exhaust gas to intake manifold Air flow in Spring (control valve) Spring Filter screen Control valve open Vacuum chamber Restriction To vacuum source Diaphragm Deflector Control valve closed To vacuum source Exhaust gas B A Figure 15-22. EGR valve operation. A—When the engine is idling, the EGR valve is closed so the idle mixture is not too lean. B— As engine speed increases, intake vacuum is applied to the EGR valve. This pulls the diaphragm up and opens the valve so exhaust gases can flow to the intake manifold and into the combustion chambers. (General Motors) Air cleaner Relief valve Air pump Orifice Air bypass valve or diverter Check valve Air manifold Air injection nozzle Unburned fuel is ignited Intake manifold Vacuum hose Exhaust valve Figure 15-23. An air injection system uses a low-pressure air pump to force fresh air into the exhaust ports or exhaust manifold. This makes any unburned fuel burn to reduce emissions. A diverter valve blocks air injection on deceleration. A check valve keeps exhaust from entering the air line. (General Motors)