system lean codes

[truckdude239]

ive been battling p0171, p0174 syatem lean bank1 and bank 2 i've already replaced the intake gaskets, i do not have a brake booster but i have the van plug in the back of the intake not leaking, ive cleaned the mass flow air sensor, no change will set lean codes after about 30 mins of driving, fuel pressure is 60psi, so im left with either a bad mass flow or 2 bad oxygen sesnors whats the best way to tell which i need without throwing parts at it? motor is a 2004 silverado 4.8 4l60e running an corvette filter and ac delco ep381 fuel pump.