I own a 2001 blazer 4.3lt 4 door 4wheel drive. I was having a hard starting problem several attempts to start before it would run on a few occasions it would back fire through the intake manifold. Researching pointed to fuel regulator. Put fuel pressure gauge on key on engine off got 55 to 60 psi it would drop to 48 or so. Changed fuel regulator (inside intake manifold) Inside the manifold it was pretty carbonized except under the regulator so I thought this was most probably the problem. When everything was back together I had no fuel pressure. Even though I could hear the fuel pump with the key on. I thought since the pump was on the old side maybe I could hear it but it wasn't pumping. I dropped the tank and changed the pump and fuel filter. Put pressure gauge back on and no pressure (0psi). I can hear the relay click and the pump. What did I overlook or screw up??