Have a 2003 for expedition 5.4 L. I have been having problems with this that no one can figure out for some reason. I have no accelaration when driving. It just revs up. I took it to a local machanic and a fordalership. They said change the egr valve so I did that and the dpfe sensor. It still runs bad. I have two codes p0171 p0125 I have checked for vaccum leak. I changed my o2 sensor and mas air flow sensor. Now my check engine light is on and I drive it and the engine keeps running but all power falls off.
P0171-Check the injector pulses. Pull the catalytic converter and give a quick test drive. If you can, buy a pipe that will fit in place of the converter temporarily to test it. If the power comes back, replace the converter.