Ok, back to this problem. Serial number om314427. 8.1 mercruiser. We put new regulator in and have a pressure of 43 it idle. Key on engine off 50, then when pump shuts off it holds at 34. What our problem is now is it is hard starting and once it does start it only runs for 4-5 seconds then shuts off. Fuel pressure holds at 43 while running. Swapped IAC from side to side, no change. When it's trying to start it reminds you of a carbed engine with a stuck choke. Like it's catching on most cylinders and winding up but just won't start. Then it finally does. We removed and cleaned fuel rail, replaced injectors, new filters and fresh gas.