With the key turned on my psi is 42, but immediately starts to drop to zero. I just replaced the pressure regulator because when I had the old one on with car at idle my fuel pressure was at 57 psi and would not drop when I hit the throttle. So I think my fuel pump is going bad. I have ruff idle and drives bad. So what do you guys think? Should I check some other things out before I replace the fuel pump?

 

You probably have a leaking injector.

 

How can I check for that?

 

If you mean KOEO, and the fuel pressure drops quickly it could be regulator, fuel pump or injectors. If you mean engine on and pressure drops, could only be fuel pump.

To check a leaky injector, unbolt and lift up the fuel rails so you can see the nozzle of the injectors. Prime the fuel pump and visually look at the nozzles to see which ones are dripping.

 

That is what my car did when my fuel pump went bad. same thing. pressure would jump up and then fall down. with key on and engine not running it would jump to 38 and over 3 seconds fall to almost nothing. when cranking (hard to crank sometimes when cold) the engine it would crank and then idle rough for a few seconds. fuel pressure at idle was 30-36 a few weks before pump went bad. It will go out when you are intraffic or away from home abd it will suck. I got 140k miles out of my stock pump. Check your fpr/injectors too. How many miles on your pump? If it is high mileage (80K-up) I would go ahead and replace it. Most guys on this board are here to learn how to upgrade their cars and if you wanna have a hot rod, go ahead and do a new pump IMO.
I got the Walbro 255 l/hr from Summit $129 and it is a great pump. Summit has it listed as a Granatelli fuel pump but it is a Walbro actually.