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P0174 and P0171 Diagnostic Issues on 1998 Ford F-150 - Recurring After Fuel Filter Replacement

Model: 98 f-150 Fault Code: P0171 Posted: 2007-11-18 20:22

My 1998 Ford F-150 is showing diagnostic trouble codes P0174 and P0171. A mechanic inspected the vehicle, replaced the fuel filter due to a suspected clogged filter, and claimed the codes disappeared. However, after approximately 100 miles, both codes reappeared. The issue persists despite the repair. What could be causing this recurring fault? I'm looking for accurate technical insights on possible root causes related to these specific OBD-II codes in this model year and engine configuration.

Related fault codes
P0171P0174
Comments (4)
Anonymous 2007-11-19 10:02

There are numerous known issues with P0174 and P0171 on 1998 Ford F-150 models. These codes often point to vacuum leaks or fuel system imbalances. I recommend checking dedicated forums for detailed discussions on these same codes in this specific vehicle. Also, consider seeking a second opinion from another qualified mechanic with experience in older Ford trucks.

Anonymous 2007-11-19 18:45

Is it normal for my truck to run poorly when P0174 and P0171 are present? Could these codes affect engine performance under load or during acceleration?

Anonymous 2007-11-19 20:05

The vehicle may run normally or exhibit poor performance depending on the severity of the underlying issue—such as a vacuum leak. Common problems in older F-150s include cracks or holes in PCV hoses, particularly near the rear of the intake manifold. If the engine is running poorly, avoid long drives until repairs are completed to prevent potential damage. How does it idle? What's its behavior at highway speeds?

Anonymous 2007-11-20 05:54

The truck runs smoothly at idle and under normal driving conditions. I'm planning to take it back in tomorrow for further diagnosis. Should I advise the technician to inspect for vacuum leaks or check intake manifold gaskets as potential causes?