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lucittm lucittm is offline
Manassas, VA
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Join Date: Apr 2007
Posts: 1,211
As far as I know the 930 and 965 fuel pumps are on all the time. They build pressure and the pressure regulator in the fuel distributor sends excess pressure (flow) back to the tank.

Voltage will not increase with load because you only have what the battery/alternator can send, about a max of 13.8V. However current will increase with load in the form of higher resistance in the pump motor as the motor slows down under load, but this is slight due to the dumping of excess flow as described above.

Do a flow test on your fuel pumps. The pump should flow 51 oz. in 30 seconds from the output hose on the filter. That is a qualitative test. For a more quantitative test get a pressure gauge and measure 91-94 psi at the same point, this is your system pressure.

Then you have to test the control pressure as the fuel leaves the warm up regulator and goes into the top of the fuel distributor. It should be 50-60 psi depending on the ambient temperature and elevation above sea level.

The system pressure can be adjusted with shims in the fuel head, but only after determining that there is no other cause for reduced pressure such as a clogged filter, worn out pump, etc.

Good Luck,
1991 964 Polar Silver Metallic Turbo Coupe
Old 07-19-2010, 05:46 AM
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