2006 Ford F150 4.2L with 253k Miles: Persistent PO171 and P0174 Codes After Multiple Repairs
Hello everyone, I'm currently troubleshooting a recurring issue on my 2006 Ford F15-0 with a 4.2L V8 engine and 253,000 miles. Despite replacing the ignition coil pack for the second time, cleaning the MAF sensor, and replacing spark plugs and wires about 2,000 miles ago, I'm still seeing persistent diagnostic trouble codes PO171 (Rich Mix in Bank 1) and P0174 (Rich Mix in Bank 2). I recently purchased new oxygen sensors but have not yet installed them. I haven't detected any visible vacuum leaks, though this remains a possibility. I've read that issues with the PCV valve or EGR system could contribute to these codes. However, I'm seeking input from owners of similar vehicles—especially those with high mileage and the same engine—on what might be causing this issue. I want to avoid unnecessary repairs and spending money on components that aren't actually at fault. Any real-world experiences, diagnostics, or suggestions would be greatly appreciated. Thank you in advance for your time and insights!
Thanks for sharing—this is a common issue on high-mileage 2006 Ford F150s with the 4.2L engine. Many owners report PO171/P0174 after MAF or sensor replacements, and sometimes it's related to EGR valve sticking or a failing PCV system. Have you checked for carbon buildup in the intake manifold? Also, ensure the O2 sensors are properly installed before testing.