1984 533I fuel pump problems

["Smith, Robert III" <RS9W@xxxxxxxxxxxxxxxxxxxxxxxx>]

The external fuel pump on my 1984 533I is making a "whining" noise.  In an
effort to troubleshoot the problem I have done the following.
1.	Crawled under the car at the passenger side rear end and confirmed
the source of the noise.
2.	Disconnected the power supply to the external pump.
3.	Opened the trunk.
4.	Exposed the top of the "in tank" fuel pump.
5.	Disconnected the fuel line on the outlet end of the "in tank" fuel
pump.
6.	Cranked the engine and no fuel came out of the outlet line from the
"in tank" pump.
7.	Checked the power supply to the "in tank"  pump and it was okay.

I surmised that the external pump is literally "whining" because it is
having to work a little harder because the "in tank"   pump has failed or
the filtration system on the tank pump is clogged.  Before I change out the
tank pump I wanted to ask our learned group if my logic and approach is /was
sound. Should I just replace both pumps?
Is there an acceptable amount of noise that is made by the external fuel
pump?  Should I have expected to see fuel emerge from the "in tank" unit
when the engine was cranked?  
Aside from the noise the car runs fine.  I understand that the car can
function with just the main pump as the tank pumps serves to help prime the
line, prevent vapor lock etc.  It pumps at a very low pressure.    As
always, help and or wisdom on this matter is greatly appreciated

Thanks

Robert Smith III

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