hey, I’m throwing code p0171 on my 1999 Ford Explorer 4.0 EFI. So I looked it up and did a few things. I cleaned the MAF sensor and replaced the air filter, that did not keep code out. So I replaced the oxygen sensor on bank 1. Not sure where else to look. I do know that the engine seems to be running fine however it is using a little more gas then normal. I do know that my fuel neck needs to be replaced because after we replaced the oxygen sensor on bank 1 it threw a code for large evap leak and whenever your standing back by the fuel cap you can smell a little fuel vapors. Can the fuel neck be causing the computer to throw a p0171 code?
Most likely reason for code P0171 would be an intake leak. The intake gaskets are little rubber o-ring style gaskets. It is common for them to fail at this age.
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
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).