98 yukon trouble codes, where to begin?

[Korn]

I have a 98 yukon with 140000 miles on it, it runs great. The only exception is that the check engine light keeps coming on. I have an Innova scan tool that I just bought and these are the two codes it is giving me. po171 and po174. I have searched all over and cannot find the fix for these two codes. One says a lean condition on bank 1 and the other on bank 2. Well I cannot figure out what part to fix. Has anyone else had this problem, if you did what did you do to fix it.

About 2 months ago I replaced all 4 oxygen sensors, it didnt help.

 

[SunlitComet]

Dirty MAF sensor. Clean it up make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling.

Inspect all vacuum and PCV hoses

Check for a dirty fuel filter and proper fuel pressure

---------- Post added at 05:24 PM ---------- Previous post was at 05:20 PM ----------

What ever it is it is something both cylinder banks share.

 

[Korn]

I just cleaned the MAF, I went to the parts store and got the proper cleaner for it. I inspected all the vacuum hoses, I also checked the pcv valve. I changed the fuel filter about 3 months ago, the only thing that I am suspecting is the fuel pump. I installed an aftermarket fuel pump from Orielys auto parts store and I think that was a big mistake. I am going to get an ac delco pump next week. Once I put the new fuel pump in I am going to clear all the codes and try it again.

---------- Post added at 06:33 PM ---------- Previous post was at 06:29 PM ----------

Dirty MAF sensor. Clean it up make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling.

Inspect all vacuum and PCV hoses

Check for a dirty fuel filter and proper fuel pressure

---------- Post added at 05:24 PM ---------- Previous post was at 05:20 PM ----------

What ever it is it is something both cylinder banks share.

effecting both cylinder banks, good point. Thanks for the help

 

[Korn]

Well I checked all the vacuum hoses, checked for an exhaust leak, I even sprayed carb cleaner all around the intake manifold to check for a leak. Nothing, after clearing the codes its still giving me the same codes p0171 and p0174 lean on bank one and bank two. The only sensors I have not changed are the map sensor and the mass air flow sensor, other than that I have changed all 4 o2 sensors, cam sensor, air intake sensor, coolant temp sensor, Im not sure what else to change. Any ideas, how do I check to see if the catalitic converter is pluged. I checked the fuel pressure and its at 56 pounds when ideling and I have replaced the fuel pressure regulator and the fuel filter.

Any ideas???????????????????????????????