How does the lift pump increase preasure?
 

2002 dodge ram 2500 and recently my truck was acting up like it was missing and so i ended up having it towed because it died and my mechanic said the lift pump is only getting 6-7 volts but will run full power if jumpered. I went to pick it up so i can test wiring instead of having to pay for a lot of labor and went and it started just fine with no jumper to power but when driving it has loss of power as i push the throttle to the floor. When idling and i push it down it misses but fuel pressure the whole time is like 15psi. Now how does the pressure increase with engine rpm as i push the throttle, does the lift pump start at a low voltage and then increase to keep up with fuel demand? Or does it always have 12volts at the pump power wire? Im guessing my airdog pump took a crap. Its a direct mount 150 psi one