Engine Sputtering after 351W swap(EFI)

[jimberg]

Do you have the vacuum line hooked up to the fuel pressure regulator correctly? If not, you will run richer as your vacuum increases. Fuel pressure needs to drop as vacuum increases and vice versa.

Have you run any injector cleaners, octane boost, or other harsh chemicals other than gasoline through your fuel system? Some fuel pressure regulators may be sensitive to certain alcohols and the diaphragm will deteriorate causing fuel to leak into the intake manifold.

A stock fuel pump is no where near being capable of supporting a 351 with 30# injectors. You would need at least a 155lph pump. I would not try to open it up with that small of a pump, but I don't think it's the cause of your problem, as you have already stated.

You may want to share your cam specs, too.