I have a 1998 F150 V6 4.2L. The check engine light is on and has the codes P0171/P0174. I have ask and searched for answers here and see that the most common causes would be the PVC/DPFE sensor or leaks in thier lines. I went to check for the PCV and saw that the truck did not have one. It had a hose going from the intake air line just before the throttle body to the drivers side valve cover with an plastic elbow to connect it but no PCV in it. Is this suppose to have one? I did buy one as the book at autozone listed one for it but I had to remove that plastic elbow and replace it with what came in the package to make it fit. I check the lines for leaks and didn't find any but unfortunately the error codes came back.

I was told the O2 sensors made cause this if they are not working properly. I replaced the two before the convertor last year and have drove about 25,000 miles. I didn't realize that there were two more after the converter until recently so those two have never been replaced. It has about 138,000 total miles but I haven't seen any codes saying that they are bad. Would these cause the error codes I'm getting? If they are not causing the error codes should I replace them anyway. Replacing these are pricey as they are about $50 each.

Thanks,
Gary

 

I highly doubt they are bad because you are getting bank 1 and bank 2 lean codes. I had this problem for quite some time and stumbled across a site where the guy told me to change the isolator bolts and gaskets on the intake manifold. It worked, no more codes and truck passed NYS inspection

 

Check he right valve cover for the PCV valve, the hose goes to and attaches to the back side of the upper intake manifold.
The left side does not have a PCV valve, it is open to allow clean fresh air from the induction system to supply fresh air into the engine, in order for the engine vapors to flow out thru the PCV valve/hose to be burned.

 

The O2 sensors can contribute to the code if they get weak, but they are still reporting a lean condition. The P0171 and P0174 are not O2 sensor codes. They usually indicate that you have an intake leak. You were on the right track to address the PCV valve, but apparently there is another leak somewhere.