Pump builds pressure but not full pressure on same faucet iv always used

you got it, don't open 2 valves, the water pressure drops and there is less flow.

Your 'on' pressure and 'off' pressure settings are too close together.
For example - you turn the pump on at 25psi and off at 26psi.
The reason it runs with the faucet open is the pressure is not building quickly enough to turn off the pump.

cHECK YOUR SCREEN WERE THE WATER COMES OUT
UNSCREW AND CLEAN
mIKE

Clogged cold water nipple or clogged hot water nipple.
Is water hot at drain valve?
http://waterheatertimer.org/Low-hot-water-pressure.html

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shut off pump breaker at the lowest faucet drain completely. Turn it back on. If this doesn't work, you have to change out the pressure valve on the side of the tank. it's not hard.

Make sure the injector is turned on. Clean the nozzle or the strainer if either are clogged or blocked. There may also be dried chemicals in the injector; dissolve them by running warm water through the injection tube.
Check to see that the faucet is open if the engine is running but the pump is not building maximum pressure. If the unit has been stored in freezing temperatures, you'll need to thaw it out completely, including the gun, wand and hose. There may also be air in the pump. Allow the engine to run with the gun open and the wand removed until a steady stream of water is released. In addition, make sure the adjustable pressure knob is set to the maximum position,
Clean the nozzle if the engine is overloaded, as the nozzle may be partially blocked. Reduce excessive pressure by using the pressure adjustment knob.

Faucet water pressure is usually a function of the city's pressure to your house. At the time of the failure, please check other faucets, or ask a neighbor if they have the same problem.
Turning the faucet off allows the pressure to build back up, but does not fix the problem.
I have seen new construction sap water pressure as they load their water trucks often leaving whole areas without pressure.

Every faucet and shower have a water saving restricter in them. Remove them from the shower head and end of the faucets.
They are about the size of a dime and with about 1/8" hole in them in which water flows out. So the flow is getting restricted from 1/2' flow to this giving you a water saving about a 1.5 gpm.

Below is some more information for the web site please check it out for further help.
http://www.inspectapedia.com/water/Poor-Water-Pressure-Diagnosis.htm
Poor water pressure just at certain plumbing fixtures? poor cold water pressure, hot water pressure, or both hot and cold water pressure or flow that is observed just at some plumbing fixtures in a building while flow and quantity are good at others suggests that the water flow or pressure problems are local to certain runs of supply piping or to the specific fixtures. Check the following first:

1. Clogged aerator or strainer on sink faucets - clogging by dirt, debris, corrosion, can significantly reduce both hot and cold water flow at a sink where the strainer needs cleaning or replacement. Unscrew the strainer from the faucet and turn on the water - if the fixture pressure or flow is much better you've probably found the problem.
   
   Look at the aerator/strainer: inspect it, clean it, perhaps soaking it overnight in vinegar to remove corrosion and mineral build-up, or just install a new aerator/strainer.

I have moen kitchen faucet # 7560 and water pressure very low. What should I do? We check water flow in pipe it is ok. I changed cartridge as well as pipe nothing help. Please let me know. thanks

Try pumping it and covering the hole with your finger until pressure builds. This usually works. Soap is heavier than water and it takes a little longer to move up.