I have a 2001 F150 V6 and getting system too lean bank 1 and bank 2. What part did you replace to fix these codes?

 

There are a bazillion threads on that subject, search p0171/174.

But mine was plenum gaskets and isolator bolts- 10 times out of 9 that will be it. Do a total vac line check first and PCV system. If that dosen't do it then it's probably the gasket/bolt thingie.

Good luck

 

plenum gaskets are the number 1 problem ... i do about 20 of these a year in the ford 4.2s

 

Another for intake gaskets and isolator bolts.

 

If you have the composite intake, its the isolator bolts. If you have the aluminum intake, try replacing the gasket and checking PVC lines. Oddly enough, mine was an exhaust leak/bad cat.