Mark VII V8-302 5.0L HO (1986)
Air Injection Bypass Valve: Testing and Inspection
Air Bypass Valves
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.
Normally Open Air Bypass Valves With Vacuum Vents
1. Disconnect the air pump supply line at the outlet.
2. Disconnect all vacuum lines from the vacuum nipple and the vacuum vent (Fig. 2).
3. With the engine at 1500 rpm, air pump supply air should be heard and felt at the outlet (Fig. 2)
4. Using a length of vacuum hose with no restrictors or devices, connect the vacuum nipple to one of the manifold vacuum fittings on the intake
manifold. With the vacuum vent open to atmosphere and the engine at 1500 rpm, virtually no air should be felt at the valve outlet and virtually all air
should be bypassed through the silencer ports.
5. Using the same direct vacuum line to an intake manifold vacuum source, cap the vacuum vent. Accelerate the engine to 2000 rpm, and suddenly
release the throttle. A momentary interruption of air pump supply air should be felt at the valve outlet (Fig. 2)
6. Reconnect all vacuum and thermactor lines. 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.
