Fuel Pump Buzzing
I have found that in cars equiped with two fuel pumps that the pump making the louder buzz is NOT the one that is to blame. It is the fault of the pump upstream from there. The buzz happends because of a lack of either fuel volume or fuel, I'm not qutie sure. However the pumps will buzz a little bit under normal opperation. But if you can hear the buzz inside the car fairly well than there is a pump problem.
I had the unfortune of changing a noisy secondary high pressure fuel pump on my 78 928. I learned that this pump only came on 78 to 79 1/2 cars and only on the 928, nothing else. I was so happy when I got the pump because I could put it in and be on my way in about 30min. However once installed the new pump was now making the loud noise. DOUGH! I then proceeded to check the pump that was making NO noise and found it to be jammed. The 1st pump is replaceable with a VW pump, however it is trickier to install because it doesn't have the check valve in the neck of the pump. So I changed the primary pump with one I happened to already have in the basement and threw the VW pump in the box for the core. That fixed it all up. I did notice though on my 78 there is only a rock filter in the gas tank before the pumps, and a very good stock filter after the pumps. It just so happends that ANYTHING going in to thoes Bosch pumps will jam them right up.
Hope this helps ya'll
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