po172 and po175 bank 1 and 2 rich

[mike340duster]

This is my first post on this site. I figured I would try here since your great member posts helped me to fix my vibration in my Mountaineer due to lack of friction modifier in the rear differential.

Here's my problem, the Mountaineer says it's running rich on both banks. PO172 and PO175. I just had it in the shop for two days and they couldn't seem to find the issue. Here is the list of the items they checked the air filter, PCV valve, looked for vacuum leaks, DPFE sensor, O2 sensors, Mass airflow sensor, EGR valve, fuel pressure( a little high at 70 psi koeo), fuel pressure regulator not leaking, and regulator is discontinued from Ford and N/A from Napa.

I'm at a loss here. Has anyone experienced a similar problem? I know I'll never pass emissions this way. My Moutaineer is a 99 with the 5.0 and is AWD. It currently has like 184k miles but runs great and doesn't burn a drop of oil. Any help would be greatly appreciated and Thanks in advance.

 

[jlsparky7]

Seafoam, plugs and wires is a good start. How to vids in the link in my signature.

 

[2000StreetRod]

FPR location

Your 1999 has a returnless fuel system. The thing mounted on the fuel rail that looks like a regulator is a fuel pressure damper. The fuel pressure regulator is located in the fuel tank. I believe that 70 psi is still within specification.

A clogged air filter would be a good candidate but that has been checked. An inaccurate MAF sensor would be my second guess but that has been checked. My third guess would be degraded O2 sensors due to age or contamination but they have been checked. The engine coolant temperature reported to the PCM significantly affects the air/fuel ratio. I suggest that you check the engine coolant temperature sensor (not the engine temperature sending unit). It could be reporting the engine coolant as cold when it is actually warm. The shop should have checked this by monitoring the ECT via an OBD scan tool.

 

[mike340duster]

Thanks for the responses. I ended up bringing it into the dealer, and it turns out it was the mass air flow sensor. The first shop told me they checked it, but I guess they missed something. I know I probably spent too much but I'm happy the issue is now resolved. Thanks again for your help.