I have a 91 lesabre that is not running good. Recently it started having problems as it would run good for 5 miles and start to sputter like running out of gas and stall. Wait 5 mins and it would run again for another 5 miles and start all over. I changed the fuel pump and filter. It still does the same thing. It starts at 32-34 psi when you first start it up. I believe it should be at least 40, but it runs good for maybe 5 mins. Then the fuel pressure begins to drop and drop until its running at 10 psi and can barely keep running and will stall. One strange notice is when it is first started and running good, when I remove the vacuum line on the side of the fuel regulator it will jump up to the lower 40s for a few mins or so. Then after time will act as before dropping pressure. There are no leaks there is nothing wrong with the fuel line. Does that mean the regulator is bad?

You have a pump problem. The PSI should go up with the vac line off. Is there fuel in that line? If so the regulator is bad. But the psi dropping tells me the pump is definitely bad.

What brand of pump did you install? Was it a GM or A/C Delco ?

This also could be a filter or sediment clogging things up. If the filter has never been changed (or history unknown), it may be worth a shot trying to change it to see if that changes things. Otherwise, it looks like the fuel tank needs to come down for a good cleanout and pump replacement while out.

So both pumps the old pump and the new pump is both the same problem causing the same thing? The PSI did go up with the line off.

Yes there was plenty of fuel in the regulator. I took the old one off, waiting for the new one, and it has plenty of gas in it but is that not normal with it being hooked up to the injection port what ever its called metal tubing going from the fuel in to the injectors and ending up at the regulator then going into the fuel return line back to the gas tank. Ive seen different kinds of regulators. This is a solid one piece type type. The fuel return lines screws directly into the regulator. But gas did not come out of the vacuum line hole. So I assume it is one piece but is separated internally and sealed. Seen below for the devise. Not the type that has the clip and comes apart.

https://www.ebay.com/itm/Fuel-Inject...W/124018799253

ebay pump says team alpha but that is also the name of the company.

https://www.ebay.com/itm/Fits-1984-1995-Firebird-Camaro-Cavalier-Steel-Electric-Gas-Tank-Fuel-Pump-E3240/254209918926

Brand brand new filter brand brand new pump. basically a brand new tank or like new. The tank and pump and filter where all changed last week. Tank was slightly used but looked like new.

The book says to test it by turning key on not starting and it should read 40. It reads 0 that way. The sec or 2 the pump runs like that is not enough to make a reading. When starting it originally after sitting for time it takes a while for it to get gas to the engine to start it. Prob 4-5 times of turning it over for say 3 seconds. I just find it odd that both pumps the old and the new would be the cause of the problem that is acting exactly the same. Its not like its not at all working. Ive never had a pump that when it went bad it just worked for a while and then didn't then did after resting. They always for me in the past just took a **** for the last time and never worked ever again. I do have another used, but almost new pump, that came with the tank.

I have a question on the lines coming out of the tank. There are 3 metal lines. One is the direct fuel going to engine. One is the return line going back to tank. What is the third line? Just for air? That line where ever it goes is mostly gone rusted away but been like that prob for a half a decade and never caused any problem before.

I believe the third line is for the EVAP system. That would go to your Canister vent valve and your purge valve on your engine. As I have not owned a Series One 3800 I could be mistaken. My first FWD GM car was a 1997 Bonneville with the Series 2 engine. There was always a slight smell of gas due to what you described with yours: a rusted out line from the tank.

I confirmed the books way of testing is full of crap. It says hope up the fuel pressure tester to the spot on the engine and turn key on. It reads 0, Did this on my perfectly working 98 Le sabre and it read 0. Even when running it took a good amount of seconds for the gauge to go up to the lower 40s. When I disconnected the regulator on there it went up to 50

I installed a new fuel pres regulator. Did nothing. Same thing. What causes pressure to slowly drop? Happened with the old pump and filter and regulator, happens with the new pump and filter and regulator. Could it be a line partly blocked? But if I put the tester after the filter where these is nothing but a hose up to the filter that would rule that out if it drops there also.