GM Repair Problems? Ask GM Repair Expert Now.
Hello, My name is ***** ***** I'll be happy to help. It sound like your going to bed a new fuel pump. The 1996 vortec needs a minimum of 55 psi at all times or it will not give you the P0300 random multiple misfire. The P0171 and P0174 are telling you that the system is to lean or to rich. Most of the time when I see those codes together it is the intake manifold gasket, a vacuum leak. You've ruled them out worth the carb cleaner. The last thing it could be is the new fuel pump. Please let me know if you have any other questions. Thank you.
I'm not sure if I was clear. Your isle pressure is within range but under load you need 55 psi. Thank you.