Ford Repair Questions? Ask a Mechanic for Answers ASAP
Hello Eddie and thank you for your question,What year is your Pickup and what size engine are you working on?
The codes P0171 and P0174 are lean code and in 99% of all cases on your 5.4 they are set due to an engine vacuum leak and on this engine it is usually caused by a rotted out PCV supply line nipple. Its hard to see because of its location. Locate the PCV valve in the passenger side valve cover and take your hand and follow the supply line from the PCV around to the back side of the intake where it connects and check the rubber nipple to see if its rotted out and leaking. In most cases it will be. Check this and let me know the results and we can work from there there if need be.