Normally Open Air Bypass Valves With Vacuum Vents-Heavy Truck Application

1 Disconnect the air supply line at the valve outlet (Figure 5) and relief port if applicable.


2. Disconnect the vacuum line at the vacuum nipple.


3. With the engine at 1500 rpm, air should be heard and felt at the valve outlet.


4. Connect a direct vacuum line that is free from restrictions from any manifold vacuum source to the vacuum nipple on the air bypass valve. Air at the outlet should be momentarily decreased or shut off.


5. Air pump supply air should be heard or felt at silencer ports (Figure 5) during the momentary dump. Restore all original connections. If any of the above tests are not satisfactorily completed, check the air pump. If the air pump is operating satisfactorily, replace the air bypass valve.