Vacuum Motor Trap Door Test (AMERICAN Motors 4.2L (258") 6-CYL. Only)

With engine not running, remove air cleaner cover and note position of trap door. It should be closed. Remove trap door vacuum hose at intake manifold and connect suitable vacuum pump.
Apply 2 to 4 in. Hg to trap door, it should open. If door does not open, apply vacuum directly to vacuum motor. If door does not open, inspect for binding and/or distortion and adjust as required.
Replace vacuum motor if trap door swings freely. If trap door opened when vacuum was directly applied to vacuum motor, check vacuum hose for restriction or leak. Replace as required. If vacuum hose is not defective, remove reverse delay valve and test again.
If door opens, test reverse delay valve for proper operation. Reverse delay valve provides approximately 100 seconds delay before allowing trap door to completely close. To test, remove vacuum hose from yellow end of valve and apply 2 to 4 in. Hg to valve.
Note time required for atmospheric pressure to pass through valve and eliminate vacuum. If time required to eliminate vacuum is less than 4.5 seconds or more than 13.2 seconds, replace reverse delay valve.

NOTE: Make sure yellow end of reverse delay valve faces vacuum motor when replaced.