I have a 1999 F-150 with the 4.2L engine. I recently did a motor swap as the original motor was bad. I bought this truck as a project truck and have enjoyed working on it.
When I did the engine swap back in May of this year, it took a while to work out all the little bugs and quirps. However, after a while of running the truck it threw a few codes. I replaced alot of the emmission components and no more codes for several months until last month the truck started throwing the infamous P0174 "too lean bank two"... I have replaced the pcv valve and all the hoses to include the little rubber boot under the front of the intake, all 4 O2 sensors, MAF sensor, EGR, DPFE, IAC valve, new wires and plugs to include coil pack, fuel pressure regulator, and all the vaccum lines that are under the hood.
The truck runs fine, has power, but about every couple weeks or so it throws this P0174 code.
I know there are alot of threads on here about this problem and I have read many of them. I was just wondering if there was any new insight to this problem that anyone could share. It only throws the P0174 and not the P0171. I am wondering if there could be a problem specific to "bank 2" that I am over looking.
Thanks in advance. Any help would be appreciated.

 

Intake air leak on bank 2.
Look at the possibility of a gasket or the IMR shaft bushings on that side.
The code is telling you which way the fuel table has been shifted by the computer trying to adjust for the issue it can't accomplish.
It could even be a leaking injector.
These codes can be set from both a lean or a rich condition depending on when the OX sensor picks it up in the dynamic swing and how far it changes the table. First shift that goes out of limits sets the code, either direction from the same cause.
Good luck.

 

Thank you Bluegrass. I will give it a look.