P0171 and P0174 Fault Codes on 1999 Ford F-150 4.2L Engine - Diagnosis and Fixes

Model: Ford F150 Fault Code: P0171 Posted: 2008-08-09 08:45

I'm experiencing persistent P0171 and P0174 diagnostic trouble codes on my 1999 Ford F-150 with a 4.2L engine. I've already replaced the Mass Air Flow (MAF) sensor, but the codes remain. As a next step, I'm planning to try the PCV valve treatment using Seafoam. I'll perform this procedure at night or late evening to minimize visible smoke and will update the community on the results once completed.