I just installed a 4.6 in a 2001 4.0 and now I am getting 1171 and 1174 lean codes.
New Bosch MAF, swapped front O2s from a running truck, smoke tested for leaks none found but still getting codes

Could it be that I need to remap the ECU?

 

 

Nice look. Something different. What was the 4.6 doing before the swap? Did you rebuild it? new intake gaskets? injector O rings? Did you use the 4.6 ECU and AFM (not necessary if non SAI to non SAI, as I have the same swap)

 

XRAD. I bought a used engine and totally rebuilt it. I did not have the 4.6 ECU and AFM. It is not SAI

 

Ok so start with an intake leak test with spay. also check you fuel trims to see where you are (on your diagnostic scanner). I had rich lean codes driving me nuts until I replaced the O2 sensors with walkers and used an old 4.0 MAF.....