Normally Closed Bypass Valves

1. Disconnect the air supply hose at the valve outlet.

2. Remove vacuum line to check to see that a vacuum signal is present at the vacuum nipple. Remove or bypass any restrictors or delay valves in the vacuum line. There must be a vacuum present at the nipple before proceeding.

3. With the engine at 1500 rpm and the vacuum line connected to the vacuum nipple, air pump supply air should be heard and felt at the air bypass valve outlet (Fig. 1).

4. With the engine at 1500 rpm, disconnect the vacuum line. Air at the outlet should be significantly decreased or shut off. Air pump supply air should be heard or felt at the silencer ports.

5. If the normally closed air bypass valve does not successfully complete the above tests, check the air pump. If the air pump is operating satisfactorily, replace the air bypass valve.