That is the Fuel Supply/Fuel Transfer pump not an auxiliary/extra fuel pump under the primer pump.
Putting a pressure gauge between the filter and the out let of the Fuel Supply pump and measure the pressure.
See post #3 for some specs.
http://www.peachparts.com/shopforum/showthread.php?t=234158
There is also a part called the Overflow Valve that is on the opposite side side of the IP
Some info on the Overflow valve is found in this thread but ignore the title of the thread.
http://www.peachparts.com/shopforum/showthread.php?t=234609
Have you tried running your car with the fuel inlet hose in a separate container of diesel fuel?