I have a 2001 ford f150 4.2 6 cylinder... cylingder 3 Missfiring and system running to lean bank 1... Im so stumped the computer is throwing two codes P0171 & P0303.. I replaced coil pack, spark plugs, wires, passenger side cat, all oxy sensors, mass airflow, im about to do the fuel filter tomorrow... anybody have any sugestions??? please help

 

Now I am not 100% if your vehicle and mine will be the same problem, but two years ago I had the same codes on a 1997 expedition with the 5.4. Like you I decided to try and tackle it. Long story short, dealership replaced some wiring harness. Cost me around $950 since then it has run great. Sometimes codes do not pinpoint a problem, but rather give you a direction to look. In my case, I ran out of options and had the dealer do a $99 diagnostic and they figured it out pretty quick. I know the thought of turning your truck over to the dealer may be sinful, but if you have exhausted all options it may not be a bad idea.Hope this helps

 

Thank you... im def taking that into consideration, anybody have any other suggestions