Ford Code P0171 1997 Ford F150

1997 Ford F150My truck has been experiencing a rough idle. After getting a diagnosis I was told that my truck was running rich. I then had a full tune up done on my truck and change the fuel injectors. Now my truck is running lean. What’s wrong with my truck? Help.


First place to start would be to pull any diagnostic trouble codes. Autozone will do this for free. Then post the codes below in the comments. For now I will just guess what code you have.

Ford Code P0171 – Fuel Injection System Too Lean Bank 1

Ford Code P0171 Possible causes

  • Intake air leaks
  • Faulty front heated oxygen sensor
  • Ignition misfiring
  • Faulty fuel injectors
  • Exhaust gas leaks
  • Incorrect fuel pressure
  • Lack of fuel
  • Faulty Mass Air Flow (MAF) sensor
  • Incorrect Positive Crankcase Ventilation (PCV) hose connection

If the P0171 is combined with the P0174 code, it’s very likely that the problem is caused by an intake leak. When there are no intake leaks, the next step is to replace the air filter and clean the air flow meter. If the problem persists the front oxygen (O2) sensor may need to be replaced.

Ford Code P0171 Description

With the Air/Fuel Mixture Ratio Self-Learning Control, the actual mixture ratio can be brought closely to the theoretical mixture ratio based on the mixture ratio feedback signal from the heated oxygen sensors 1. The Engine Control Module (ECM) calculates the necessary compensation to correct the offset between the actual and the theoretical ratios.
In case the amount of the compensation value is extremely large (The actual mixture ratio is too lean.), the ECM judges the condition as the fuel injection system malfunction and light up the Malfunction Indicator Light (MIL) (2 trip detection logic).

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