We change the pull down sprayer for a universal one that home depot sales. When this installation was done the sprayer has pressure but when faucet is used there is no pressure.

Is this a kitchen sink or shower or something else?

Sprayers and spouts aren't supposed to work together. You have a diverter in your valve. Every time you press the sprayer button the diverter closes the spout. If they both run at the same time you have a faulty diverter. The diverter's located in the front of the valve under the spout. You could have trash in there preventing the diverter from doing its job. Check it out. Good luck, Tom