Air Bypass Systems Diagnosis

1. Start engine and allow to reach normal operating temperature with transmission in Park or Neutral and parking brake applied.
2. Stop engine and remove air check valve hoses at bypass valve. On engines with two check valves, disconnect both hoses connecting bypass valve to check valves.
3. Connect tachometer to engine. Accelerate engine to 1500 RPM. Check that air is flowing from air bypass valve hose connection(s) by placing hand over valve connection. Air should be heard and felt.
4. Disconnect vacuum hose from bypass valve and plug vacuum hose. With engine speed at 1500 RPM and hand placed over bypass valve connection, there should be very little air flow heard or felt. Air should be discharged through the exhaust vents in the end of the air bypass valve silencer cover. If air flow is felt or heard through the bypass valve connection, the valve is defective and should be replaced.
5. Stop engine. Remove plug from vacuum hose and connect hose to bypass valve sense vacuum nipple.