I have a 2000 blazer 2 door 4x4 4.3L, I have checked all of the other threads and have not found one with my specific problem. I was checking my fuel pressure yesterday (bored at work, nothing to work on at shop) and I noticed when I turn the ignition on and the pump cuts on for 2 seconds, the pressure goes to 55 p.s.i and then just swiftly drops down to about 45 p.s.i....,but wait I know you might be thinking its the fpr or spider assembly but thats all new. So here's the kicker THE PRESSURE SLOWLY INCREASES BACK UP!!! WTF!!! I changed the fuel filter thinking that was causing the pressure to slowly increase but still is doing the same thing..

Anyways thanks in advance.

 

Wow... you were bored eh? lol

 

That sounds like a fuel pump relay starting to go bad to me. If the relay is going bad then it may not be sending constant voltage to the pump which would account for your odd pressure fluctuations.
Low voltage to the pump will also burn it out quick so you might want to check it out ASAP.

 

The initial pressure drop after the pump shuts off could be from the check valve closing a bit slow. The rising pressure could be from the fuel coming out of the tank and heating up.

All in all, if the truck is running/starting properly, I wouldn't worry much about it.

 

the check valve is made into the pump assembly itself correct? would it cause any kind of performance problems if the check valve was weak or going out?

thanks!!!

 

The check valve should be all the way open when the pump is running. I suppose it could cause a restriction in the supply line if it wasn't opening up all the way, but you would see that as low fuel pressure when you are driving under load.