1993 Ford Mustang Fuel Pressure Regulator

Thanks, mac. I did get a new regulator but there was no change. I am still running with no vac line but air is going out. What happens if air just goes out? Seems like higher PSI gives me more boost. Old motor can't run on low fuel. I have a new pump too but old cat and carb have high NOX. With vac line out, the car runs with good power. What's with the vac line. If the vac line lowers fuel pressure and car can't drive should I get an adjustable fuel pressure regulator like an Aeromotive. That way I can control the pressure and have a good setting that makes old 3.4L run on higher PSI. And why is there air in vac line and what is source? Is it okay to just let air go out? Why plug it and let air be trapped? I can recheck pump and let you know if it is new and working. But why would vac line increase or decrease pressure to give power for car to drive. Seems like a minor fix but can't seem to pin down.