Engine P0171 System Too Lean

drkhrse93

New Member
Apr 29, 2017
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Hi guys,

I am having an issue with my 2000 Mustang 3.8L V6. I am getting a P0171(Passenger side cylinder bank lean) code and haven't been able to find the problem. Here's a little background information on the car and what I have tried so far:

Background: I installed a cold air intake then about four months later I installed a programmer chip and a day or two after that I got the P0171 code.

Noticeable effects:
  • At idle the RPMs go up and down as it “searches” for the happy RPM.
  • If I rev it up it will stumble when it gets to 4,000 RPM
Troubleshooting techniques I have tried so far:
  • Removed programmer and reset computer by disconnecting battery overnight.
  • Went back to factory air intake
  • Cleaned MAF sensor
  • Switched left O2 sensors with the ones on the right to see if code would go to P0174 (Driver side cylinder bank lean) but it still came back as P0171.
  • Used a simple homemade smoke machine and was unable to detect any vacuum leaks.
  • Cleaned fuel injectors and listened to each one to confirm that there was an audible noise from the internal solenoid functioning correctly (they all sounded good).
  • Placed all the fuel injectors in a jar (while still connected to the fuel rail) and cycled the key to the “on” position several times – there was only one fuel injector that squirted fuel but is that just because it was it was priming the first cylinder that would fire at engine start?
Any help would be GREATLY appreciated.

Thanks in advance!
 
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Check the fuel pump and fuel tank. Had the same issue and it was the tank and pump. The pump needs to be genuine Ford part though. Did a universal one first and ended up wasting money for it not to work.