1990 80 series Q, vacuum pump question

[Danae Kranski]

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I have had an intermittent knocking coming from the vacuum pump which is
mounted on the front of the engine.  I removed the unit and disassembled
to investigate the noise. Noted nothing abnormal but what appears to be
a port plugged with silicone. This port exits forward from the pump
assembly and appears that it could accept a hose fitting.  Does anyone
know if this port should be used and routed to some other component or
blocked like it is presently?  My understanding of the vacuum pump is
that it is used to ensure vacuum to the brake booster diaphragm when the
intake manifold vacuum is not adequate to do the job.  Is there any
other function it performs
Regards
Richard
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