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1997 Ford Expedition P0171 and P0174 Diagnostic: Misfire in Cylinder 4 and Fuel System Issues

Model: 1997 ford expedition Fault Code: P0171 Posted: 2009-02-09 20:48

I have a 1997 Ford Expedition with a 5.4L engine. I recently replaced the spark plugs due to a misfire in cylinder #4. After replacing the fuel filter and clearing the codes using an OBD2 scanner, the check engine light came back on. Now I'm seeing fault codes P0171 (System Too Lean Bank 1) and P0174 (System Too Lean Bank 2). What could be causing this? Any suggestions or troubleshooting steps would be greatly appreciated. Thanks, Eric.

Related fault codes
P0171P0174
Comments (1)
Anonymous 2009-02-10 09:45

Check for vacuum leaks, especially at the intake manifold and the PCV valve and its hoses connected to the throttle body. Also inspect and clean the Mass Airflow (MAF) sensor. Verify fuel pressure is within specifications. These are common causes of lean mixtures indicated by P0171 and P0174 in 1997 Ford Expeditions with 5.4L engines. Good luck—please update if you find a resolution.