Here is a run down of the problems. Listed as running lean I have a fuel pressure of 30psi not the 48-55psi required. all lines checked and good. Fuel pump is good. Have been told that the piston rings may be out and need replacing. Also got told that problem might be in the fuel injectors may be clogged, but wouldn't the lines be over pressure if at the end of line. However car starts fine when cold. Will not start when hot or has been running for more then 30 minutes, car must sit for an hour at least to be restarted. Makes chugging sound when initally started then evens out. Also car shimmies at 42mph and 74mph. No idea why the shake but rides fine at any other speed, odd.
P0171 & P0300, Fuel lean, random misfire. on 2001 Pontiac Grand Prix
by Spawn471030 in Virginia Beach, VA on April 12, 2011
ANSWER by Jim Taddei , April 12, 2011
You must determine the cause of your low fuel pressure. I would strongly suspect the fuel pump or pressure regulator. If you can find a way to block the fuel return line and the pressure does not go up then the problem is with the supply side - fuel pump or available voltage to it. If the pressure rises with the return line blocked (in should go over spec) then chances are the fault is with the pressure regulator. With the fuel pump running and the engine off the fuel pressure should he 53-59 psi for the standard 3.8L and 48-54 for the supercharged version.
ANSWER by mastertech6371 , April 12, 2011
I agree with Jim. I bet the pump is bad. that is the reason for not starting as the fuel pressure is too low and the fuel is very hot and almost boiling. this is also the 171 code and the 300 code. the shimmy may be wheel balance or a shifted belt in a tire. have it checked at a shop. thanks for using repairpal. Roy