I know I'm at the wrong forum, but being an owner of a Stang this is the only one I got an account on. My dad's 2003 F-150 4.2 V6 had a service engine soon light come on a few days ago. Thetruck is running completely normal though. I connected it to an OBDII reader and it gave me 2 codes which are p0171 and p0174. The explaination was "system running too lean" and that's for both, bank 1 and bank 2. I first thought it was a bad oxygen sensor, but then why would it be on both banks at the same time? I checked all the vacuum hoses and everything is seems connected right with no leaks or cracks anywhere (the truck has 54k miles on it). I know it can also be caused by a loss of fuel pressure and a faulty MAF sensor which I have not yet tested. I took off the MAF sensor to make sure there's nothing stuck inside and I didn't see a thing. Where should I start or what else could it be? How do I test a MAF sensor? What do I hook up a fuel pressure gauge to? How do I test the O2 sensors without making holes in the wiring to check the voltage? This is driving me nuts, any help is highly appreciated.

 

fuel pump or filterfilter

 

Check your PVC hose. I have a ranger edge 4.0Lthat had the same issue that you are describing. I the issue was a cracked PVC hose. It can also be a disconnected vacum line.