B4 - Vacuum Test -- Exhaust Disconnected

^ Turn engine OFF.

^ Disconnect exhaust system at exhaust manifold(s).

^ Repeat vacuum test.

^ Is manifold vacuum above 16 inches of mercury?

YES -- Go to B5. B5 - Vacuum Test -- Catalytic Converter(S) On/Muffler(S) Off

NO -- Go to B6. B6 - Exhaust Manifold Restriction