Fuel Pressure with car running varies between 20 and 28 psi. Standard is supposed to be 34-39 psi. Replaced fuel filter. No help. Disconnected fuel return line and ran fuel pump got 20 psi. How do I know if I have a fuel pump problem or a fuel regulator problem? Car is driveable, but low speed performance is bad and will often quit on idle down. Any ideas? Thanks.
'90 IROC ragtop