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!

 

Have you looked for any exhaust leaks in the manifold or flange before the 02 sensor?

 

I looked and didn't see any.

 

My guess is there is a vacuum leak your not finding. But it could be fuel filter related. Or even a stuck PCV valve. Somthing is letting unmetered air into the system, possibly a leak in the cold air intake connections.

How reliable to think your smoke test was? Unsless you used compressed air to inject the smoke I wouldnt trust it.

 

It has a pretty new fuel filter (less than a year old), I replaced the PCV valve about two months prior to the CEL coming on, and I went back to the stock air intake and I'm still having the issue, so it's not a problem with the cold air intake.

For the smoke test, I used a fire in a pickle jar and routed a hose out of it and a bicycle tire pump into it. I removed the stock air intake and put rubber glove over the throttle body in its place. I pumped smoke through the vacuum system from the opposite end and I could see the glove fill up with smoke, so I know there was smoke in the system and enough pressure behind it to inflate the glove.

You can probably see why I'm going crazy right now...