2002 Ford F150 4.2L 6-Cylinder OBD2 Codes P0171, P0172, P0174 - Diagnosis and Solutions
A diagnostic scan revealed the following OBD2 trouble codes: P0171 (Rich mixture bank 1), P0172 (Rich mixture bank 2), and P0174 (Rich mixture bank 4) on a 2002 Ford F15-0 with a 4.2L 6-cylinder engine. The vehicle was initially advised to clean or replace the Mass Airflow (MAF) sensor, which was cleaned but did not resolve the issue. A non-dealer MAF sensor replacement improved performance temporarily before the engine returned to rough running and misfiring. Spark plugs have not yet been replaced, though this is considered a potential contributing factor. The vehicle exhibits poor idle quality—especially at red lights—and shows some improvement during acceleration. No obvious vacuum leaks were detected, but fuel pressure and leakdown tests are pending. I am seeking further input on possible root causes beyond the MAF sensor. Any insights into other components or diagnostic steps would be greatly appreciated.
Check for vacuum leaks. Verify fuel pressure and perform a leakdown test. Also, try temporarily disconnecting the MAF sensor to see if the engine runs differently—this can help determine if the MAF is contributing to the misfire or incorrect air-fuel ratio.