1991 camaro 3.8L fuel pump or pressure regulator? P300 multiple misfire only. key on engine off. Fuel pressure = 42. Start engine goes up instead of down. It went up to 49 - 50 PSI. No vacumm leak. Fuel filter replaced and the old one was okay. I disconnected the vacuum line to the pressure regulator. The pressure was 50 PSI while idling. The car runs rough at low speed and runs okay at highway speed.
No gas in the vacuum line.

Is this a pressure regulator problem?

 

I'm gonna go with neither. How old are the spark plugs? Plug wires? Have you ever ran injector cleaner through the system?

 

The plugs and wires are new and the cam shaft senor checked out okay. I have run sea foam through it. The coils are okay and the module tested okay.

 

Get your injectors flow tested but it all sounds good. Were any of your plugs dropped at all? If so you need to replace them. Also when did this start happening?

 

No, none of the new plugs were dropped. This multiple misfire did not develope over time. It just started all of a sudden when I was driving to work. I do not beilve it to be injectors because i would have noticed them plugging or starting to fail over time.

 

Spark jumping somewhere intermittently? I wouldn't be surprised.

It may or may not be your pressure regulator, but I know it isn't your fuel pump. When they go bad, it isn't like this.