Originally Posted by tjwalker
Did you install the entire fuel pump assembly, or just the fuel pump?
There is a check valve in the regulator and when that goes bad, you can have a bleed down of fuel pressure and the exact symptoms you are describing.
And if the engine stumbles and runs rough for a few seconds after it starts, you could have a leaky fuel injector. That leak bleeds down pressure and then it runs rough for a short time as the excess raw fuel is burned off.
Get a fuel pressure gauge and start testing your way to the root cause here.
I Purchased just the fuel pump according to the parts store and the receipt The parts store said I can purchase just the pressure regulator. My question is now Can I replace the pressure regulator without pulling the fuel pump out of the tank? Is the pressure regulator mounted on top of the pump and or outside of the tank?