I am getting codes P0171 and P0175 on a 2002 F-150 4.2. I have cleaned the MAF and filter, replaced the elbows on the PCV assy and checked for vacuum leaks but couldnt find anything. The truck runs a little rough at idle but doesnt seem to lack any power. It is also hard to start, especially when it has warmed up. Fuel pressure holds pretty steady 32psi at idle. I have also replaced the fuel filter and air filter. Not sure what is causing the problem, any ideas?

 

you are getting a "to lean code on bank 1" and a "to rich code on bank 2". I have never see this before. I don't have any answer for you. I think I will follow the thread. Please remember to post a conclusion when you figure it out.

 

I've been told that this is likely due to a upper intake leak, think I might try that. My Fuel trim values are way out of spec.

 

Ok, so not an upper intake leak, just got done replaceing those gaskets. Could it be a properly placed exhaust leak? I think there may be a small one, just cant find it but seems this could be a possibility, I just dont know much about how these systems run.

 

your positive you have the right codes.......most of the time when you get a p0171 you will get a p0174

 

Exhaust leaks will cause lean codes. Could be a pcm problem. Possibly an o2 sensor going bad on one bank causing the other to be leaned/richened out to compensate for the lack of response from the O2 sensor? Kind of hard to tell without a scan tool to monitor PIDS.

 

I have a scan tool, is it the LTFT and STFT that would help?

 

Found a small exhaust leak on the manifold (broken bolt). That was probably causing the lean but we will see next week. Now just the rich code.

 

STFT is what you'll watch. An exhaust leak will cause oxygen to get sucked in and set lean codes.

 

Ok, so I had a small exhaust leak from a broken bolt on the exhaust manifold; fixed it and that seems to have gotten rid of the lean code. I still have the P0175 rich code on bank 2. The LTFT is -27 at idle and the exhaust still smells very rich. The only think I can think of is a leaking injector or something like that. Any thoughts.