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Air Bypass Valve (Normally Closed)

  1. Disconnect air supply hose at valve outlet. See Fig 1 . Remove vacuum line from vacuum nipple and check for presence of vacuum at nipple. There must be vacuum present at nipple before proceeding.
  2. Reconnect vacuum line to vacuum nipple. With engine at 1500 RPM, air pump supply air should be heard and felt at air by-pass valve outlet.
  3. With engine still at 1500 RPM, disconnect vacuum line. Air at outlet should decrease significantly or shut off. Air pump supply air should now be heard or felt at the silencer ports, or at the dump port.
  4. If the normally closed air by-pass valve does not perform as described in steps 2) and 3), check the air pump for faults. If air pump is operating satisfactorily, replace air bypass valve.
Fig 1: Normally Closed Air Bypass Valve
G90D14327Courtesy of FORD MOTOR CO.
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