a bad fuel pump or bad fuel pressure regulator?

Thanks,

Matt

Fuel pump- not enough fuel, low pressure

Regulator- wrong fuel pressure, cracked "sealing" makes the fuel go into the plenum via the small vacuum hose..

/N.

You can have various symptoms. Hard start, no start, starts but no power, screeching noise from the fuel tank.
The only way you can be certain is to connect a pressure gauge and troubleshoot.
Depending if it's either port or throttle body, you'll have 2 different operating pressures.
A regulator, as with a pump can be bad 2 ways.
A pump has to be able to supply enough capacity and it's the job of the regulator to bleed off the excess fuel returning it to the tank.
When you shut the system down, it should hold pressure for the next start cycle or at least hold the fuel in the line.
So with a pressure gauge connected, you should see the pressure hold and not fall back to 0.
If it falls back, it may be the check valve in the pump or a bad regulator. To isolate which one, typically you pinch off the return hose and power up the pump briefly. If the pressure now holds, its's the regulator. If the pressure falls off with the return line pinched, the pump is bad.
I know it's long winded, but I hope it helps.