Hello, I have a 2002 f150 Lariat with the 5.4L. I have been trying to figure out a P0171 and P0174 code for a few months now.

I have replaced the intake manifold gasket, the air intake, the PCV valve, the o2 sensors, the cats, the MAF, the fuel filter, gas cap, new battery.

Even with all that im stilling throwing these codes. I have smoke tested and saw nothing coming out. I have checked every hose and connection and can not see any holes or cracks.

Anyone have any idea of what the heck else it could be? I have been told PCM could be bad but im not very thrilled about that answer so im still trying to explore other options.

 

Have you checked out the rubber connection behind the short vertical intake manifold. You can't see it in place.
The rubber goes soft from the crank case ventilation fumes.
Good luck.

 

I am having the same problems as rustyp1 on a 2003, 5.4L with about 160k miles. I have not begun to shotgun the problem as of yet. Hope to be able to take a systematical approach without hitting the wallet to hard. Any divide and conquer suggestions would be welcomed.

 

It is foolish and costly to take a shotgun approach to an issue.
People do this out of a lack of knowledge about what they are trying to accomplish.
Look at the code description, then try to learn what it means, then go to the likely areas that cause the code beginning with the easiest starting point.
This eliminates much of the extra hassle and expense plus you learn from it.
The codes are telling you the Ox sensors 'both banks' are detecting to much oxygen in the exhaust. Surprise!
They cause the computer to richen up the fuel injection to ...account... for the extra air due a vacuum leak.
This is why codes are used to alert to the basic problem.
This eliminates a lot of remote/unrelated part replacements and work that won't fix the issue.
On the other end of the coin, if you took the vehicle to a shop and they shot gunned the problem, you would not want to pay for parts not needed either.
Good luck.