99 F250 LD 4x4 w/5.4 - 218k

Check engine light just came on so I had the trouble codes pulled.
071 and 074 . Lean on banks 1 and 2 . Truck is running fine as far as
I can tell. I know it can be o2 sensors, pcv, maf sensor or loose vacuum
line somewhere. I just put a new motorcraft pcv valve on before this happened so I rechecked the lines , all seem to be fine. Is there a inexpensive scanner that I can check the o2 sensors without just throwing money at new ones. or does anyone have any suggestions to try? Thanks

 

You need a little education first.
The codes are not 071 or 074.
They will be 0171 and 0174. A big difference if you look at a code list.
Next, they are not caused by faulty OX sensors so no use to try testing those sensors in any way except by monitoring their performance.
The OX sensors are the way the system reports the issue causing the codes.
What the codes mean is an air leak into the intake tract after the mass air meter.
This air is 'unaccounted for' being after the air meter.
What causes the codes is when the program tries to correct for the extra air by richening up the fuel.
When the fuel tables shift out of limits trying to correct, both codes are set because the problem is common to both banks.
Find the air leak and you solve the code issue.
Good luck.

 

Yeah, I was being lazy and not looking the codes back up. I was trying to remember them with a faulty memory. I though it was probably an air leak but wasn't sure where to start . Thanks for the great info. !

 

Just an update if anyone is interested. I checked all the vacuum lines and couldn't find a problem. I cleaned the maf sensor for the hell of it and noticed
a smoother idle right off. I cleared the codes and started a new drive cycle.
After about 50 miles no check engine light and if I'm reading this scanner correctly , no pending codes. Maybe I inadvertently fixed the problem.
We'll see!