Ok, this will be long because i'll start from the beginning.
I replaced the fuel pump with a 255lph pump a couple years ago. everything was cool. I kept the stock pump for a spare. 10 days ago the car quit.
No fuel at all, but could here the pump run. I dropped the tank and found the hose between the pump and hard line popped off. I thought thats really strange it took it 2 years to come off, but whatever. The car started but ran sick, had to pump the gas to get it to start...etc. Noticed the nylon line going to the filter was kinked. Ah Ha.. kinked line, too much pressure behind it, blew the hose in the tank! Dropped the tank again, replaced kinked line.
Still no pressure at the rail, like 5 psi that bleeds down quick. Next I thought the pump got weak from working too hard. Ordered a new 255lph pump. Dropped the tank for the 3rd time, replaced pump. Same results. I am now officialy pissed. Thinking my new 255 pump is ****ty, i put the stock pump back in. Same, so I'm convinced all my pumps are ok. I am totally out of ideas. Oh yeah replaced the filter the 1st time the tank was down.Why won't it keep pressure? If you've had a similar experiance please help.

 

for one thing your Fuel Pressure regulator could be on the blink, another thing is your pump may not be getting the right amount of voltage if all lines are clear of kinks and debris... that will cause the same issues your having. I'd go with #1 I had both problems... #2 was low pressure caused by a bad battery (ran just like you stated).. .good luck.