Ford Repair: Fuel Starved, vacuum leaks, vacuum leak

Question
Tony, Hi!
I've got a 1996 Explorer 5.0 with P0171 & 174 codes, lean both banks.  After a minute warm up the engine will sputter, back fire and has very little power.  If I turn it off and back on, it will run ok, for a minute, then terrible.  I hooked up a gauge to the fuel rail and got 30 psi till the problem starts and it slowly goes to zero.  I have 70 psi from the pump before the filter.  Have replaced the fuel regulator, filter and the pump was done not too long ago along with EGR and sensor.  Cleaned the MAF with Electro Clean and checked all connections.  Pulled connectors apart with engine running, no difference.  Checked for vacuum leaks with spray and propane.  None found.  I am stumped.  This 5.0 has no DPFE or DFE. Any ideas???  Thanks, Tim  

Answer
Hello Tim, Sounds like there is a vacuum leak either from upper intake gaskets or like a pcv hose assembly. That is pretty much what will cause lean codes to both be in the system. I know you said that you checked with propane and spray but a small leak or leaks that may not detect that way will still throw off the computer. That is where I would start 1st. Thanks Tony