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PO171 & PO174 Diagnostic - 2001 Ford E250 5.4L Engine Issues

Model: 2001 E250 Fault Code: P0171 Posted: 2008-07-28 09:46

We have thoroughly inspected and repaired the engine of our 2001 Ford E250 with a 5.4L V8 engine, including replacing the PCM, MAP sensor, fuel pump, intake gaskets, IAC valve, PCV system, and performing a full PCM reflash. We also installed a new IAC bypass assembly to eliminate the whistling noise. The exhaust system was completely removed during troubleshooting. Despite these extensive repairs, the vehicle still exhibits symptoms: upon startup, it runs at high RPM for approximately 20 seconds before experiencing a rough idle that eventually stabilizes only intermittently. During road testing, when the driver accelerates, the van loses power and appears to 'fall on its face'—it fails to respond to throttle input. However, if the throttle is gently applied (babyed), the vehicle begins to gain speed very slowly. The check engine lights are showing codes PO171 and PO174, indicating lean air-fuel mixture conditions in both banks of the engine. We suspect a persistent fuel delivery or intake leak issue despite all repairs. The symptoms suggest either a faulty sensor reading, an unsealed vacuum line, or a deeper underlying problem with fuel system integrity.

Related fault codes
P0171P0174
Comments (2)
Anonymous 2008-07-28 17:51

You mentioned replacing the fuel pump—did you also replace the fuel filter? Additionally, ensure that the air cleaner housing clamp is fully secured and properly connected around all sides to prevent air leaks.

Anonymous 2008-07-29 08:41

Try adding a supplementary fuel supply after disabling the primary fuel system. Monitor the oxygen sensors closely—observe if their readings begin to drop toward zero. If they do, this indicates a lean condition and points to potential fuel delivery issues. Perform a leak-down test on all injectors to verify proper function and rule out internal injector failures.