I ran a Holley black pump for a while. Make sure it is getting 12v, the more constant the better. It should put out good pressure even with lower voltage. I would suspect the regulator. Is it a return style or dead head style? I had one Holley style regulator that would only adjust with the car off, plus it was noisy. While running it wouldn't budge from the setting. I got rid or it in favor of an Aeromotive regulator.
