Pontiac Repair: 1998 pontiac gran prix supercharged, pontiac gran prix, fuel pump filter

Question
the car runs rough and misses especially under load. Scan tool codes were 0171 & 0306.(lean mixture & #6 cyl. misfire). I replaced#6 plug and coil.I also replaced the fuel pump, filter ,and pressure regulater.Static fuel pressure is 42# when I cycle the fuel pump without running the engine.According to the shop manual it should be between 48 & 55 psi. The pressure was the same with the old fuel pump. The pressure will go to 50# when I cycle the pump but drops down to 42# in a few seconds and stays there.What could be the problem ?

Answer
Hi jerry:

That pressure drop is normalonce the engine is running the vacuum on the pressure regulator drop the line pressure down. if you fixed the misfire and your just chasing the 171 code I would look for a vacuum leak there is a plasti hose that runs under the nose of the super charger the port then splits the line off usually that port cracks and there is a vacuum leak there or the gasket between the super charger and the intake manifold is sucked in and cuaing a lean condition there. with the engine running spray some carb cleaner under the nose of the super charger and see if the engine idle changes if it does you found the issue and then it's one or the other for the vacuum leak. good luck and happy holidays. :-)