I have a 2000 F-150 V6 with 85,000 miles. Haven't had a bit of trouble with it until just recently. My Service Engine Soon light come on while I was driving. After searching extensively for any problem, since it appears everything is running good, I broke down and purchased an OBD II code reader. After reading the handheld it only gave me two codes, P0171 (System too lean {bank1}) and P0174 (System to lean {bank2}). I had the fuel system flushed at 67,000 miles. Since the light I have tried to add gas treatment and fuel injector cleaner and have always used at least 91 octane fuel. Short of taking it in and spending what I don't really have right now, I am out of ideas. If anyone has had this problem please let me know what your outcome was so I may look in that direction first, or if anyone has any ideas, they will be greatly appreciated.

 

You say you had the fuel system flushed?? Was there a reason for that?? Have you replaced the fuel filter lately ?? Could be faulty fuel pressure regulator, could be fuel pump failing. Also did you clear the codes to see if they come back?? Just some off the top of my head ideas.

 

No, not any specific reason for getting it flushed. Ford.com just sent me a reminder to have it done at 60,000 miles. I did clear the codes at first, thyen cleared them again after adding fuel treatment, with no success. Thanks for the ideas though, I will start with the filter, hadn't even thought it may need replacing anyway, then check out the regulator. Thanks.

 

Another thing would be nice if you could aquire a fuel pressure tester from someone which hooks up on a shrader type valve on the fuel rail which would show the pressure of your fuel system then you could pull the vacum hose off of the regulator and see if pressure jumps up if it doesnt then either fuel pump or filter.

Good luck and lets us know what you finf out

 

Might be a low voltage signal from the O2 sensor causing the problem. Use a OBD II tester and watch the O2 sensor voltage should move between .1 - .9 V (.1 = lean, .9 =rich).