2002 Mustang gt 5 speed, 39,000 miles, cold air intake, h-pipe, flowmasters


I am having a problem with my fuel pressure, it is staying around 33 psi, and when i took off one of the vacuum lines it went up to 44 but still was hesistant, it is suppose to be between 40-70 psi. My check engine keeps getting tripped saying it miss fired in the number 4 cylinder and when the check engine light blinks it starts hesitating.
If anyone has had any dealings with this please let me know, before i get rid of it.....Thanks alot!!