After 2 years with p0171 and p0174 on 2002 5.4 4x2
I started out with P0171, then within a week p0174 also, I changed the fuel filter, cleaned the MAF, changes all plugs and a few coils as they failed. I changed the fuel pressure sensor, and adjusted the throttle position sensor. After about two years it still ran ok but couldn't shake the codes. it started then to get worse, couldn't accelerate very fast, would hesitate on turns and almost seemed as it the transmission was slipping horribly, as well as getting only 8mpg. Finally I took it to a shop, for 100$ they told me that the Intake manifold had a leak and wanted 1100 to fix it. I said nope and did it myself saving a lot of money, but still had the codes and still hesitated. Finally I thought it was fuel related, but didn't want to tackle a fuel pump. It ran but just acted like it wasn't getting enough gas. Everyone told me Fuel pump would just not start, not run badly. It only has 117k miles so again everyone told me fuel pump cant be bad... well it was, I finally tackled the fuel pump and after replacing it the codes are gone and it runs beautifully. I believe the fuel pump was failing slowl hence the p0171 and p0174, lean on bank one and two caused by low fuel pressure or low fuel delivery, not too much air. hope this helps someone else with the same issue.