Around 4 years ago I analyzed two pumps that were considered trash and did have problems, but electrically they were in great shape. Below are my flow results both at 12.4 to 12.6 VDC and then 14 to 14.1VDC. I didn't use my PSD for the tests, but a gasser since I was starting and stopping the tests a lot. IMHO there is a significant decrease in volume for less than full voltage at the pump. While the flow rates are obviously low it's the relative numbers that are important to give one a feel of the effects of both voltage and outlet pressure.
Pump 1:
A. Motor resistance was 1.9 ohms as measured at the exterior contacts This would equate to a current draw of around 6 to 7 amps, but I never put an ammeter on either of the pumps.
B. For 60 psi pressure, 4.5inHg suction vacuum, using fully charged car battery and engine not running the input voltage was 12.4 to 12.6 VDC. It took 6 min to pump 2.5gal=25gph
C. For 60 psi pressure 4.5inHg suction vacuum, using the same battery as Test 1 but with the engine running the input voltage was 14 to 14.1VDC. It took 4m45s to pump 2.5gal=31.58gph
D. For 70 psi pressure, 4 inHg suction vacuum, using same battery as Test 1 but with the engine running the input voltage was 14.1 to 14.3 VDC It took 4m51s to pump 2.5gal=30
Pump2:
A. For 60 psi pressure, 4inHg suction vacuum, using a fully charged car battery with the engine not running the input voltage was 12.5 to 12.7 VDC. It took 8m5s to pump 2.5gal=18.56gph
B. For 60 psi pressure, 3.5inHg suction vacuum, using the same battery as Test 1, but with engine running the input voltage was 14 to 14.2 VDC. It took 6min to pump 2.5gal=25gph
C. For 70 psi pressure, 3inHg suction vacuum, engine running input voltage 14 VDC. It took 6m30s to pump 2.5gal=23.08gph
D. For 80 psi pressure, 3inHg suction vacuum, engine running input voltage 14VDC. It took 7m40s to pump 2.5gal=19.57gph
E. For 66 psi pressure, 3inHg suction vacuum, engine off input voltage 12.3VDC. It took 8m10s to pump 2.5gal=18.37gph
F. For 70 psi pressure, 3inHg suction vacuum,
engine off input voltage 12.3VDC it took 8m25s to pump 2.5gal=17.82gph