I'm currently trying to fix my son's 2004 Expedition with the 2V 5.4L. The truck repeatedly throws P0171 and P0174. The scanner was showing me what looked like typical vacuum leak indications except... At idle, my LTFT for both banks are both right around 29% with STFT anywhere from -8% to +2% at any given time. When driving, as soon as I get going, the LTFT for both banks blast right past zero and go down as far as -18% or so. Now, I understand that vacuum leaks cause a high LTFT at idle which trends toward zero at higher RPMs. So what would make the LTFT shift to such an extreme rich condition? Additionally, with the fuel trims shifting so far negative, this tells me that fuel supply isn't an issue.
As such, I've completed the following:
- Replaced the intake manifold and gaskets
-Checked and/or replaced most hoses and fittings including the infamous PCV elbow behind the intake.
-Hooked up the smoke machine and confirmed no other leaks in the system.
-Checked electrical outputs of the various sensors.
-MAF volumes appear to be reasonable with live data and the sensor itself showed good voltage per the Chilton manual.
-O2 voltages appear to have normal fluctuation

So now what???

 

What fuel pressure are you seeing with an actual gauge connected to the fuel rail?

 

Dig the freeze frame data out for the fault codes and post that info. "Lean" codes at idle will usually caused by something different from those set at higher RPMs.

You might want to reset the KAM and start from baseline values and induce the failure. Starting with fresh data is a good practice.

Also, ensure that the PCM is operating in Closed Loop mode while making your observations. If it drops into Open Loop mode, the PCM no longer looks at the O2 sensors and instead uses internal fuel mapping tables plus other sensor inputs to determine fuel delivery.

 

Thank you both - projectSHO89 and JWA - for responding. The fuel pressure at the rail is steady at approx. 60 psi which is a little high (the manual calls for 35-55) and the hold pressure is good. I cleared everything this morning and took it for a quick spin. No codes just yet as per usual. It is running in closed loop and didn't take long for the LTFT to get to 19.5% and 24.5%. This is par for the course and will almost certainly go back up to around 29% next time its driven.

 

Include the sign (+/-) when posting trims. It's critical.

Let it code out and THEN post the FF data. Also, fuel pressure under failure conditions would be helpful to know.

 

Just took it for a rip and here's the FF data for the pending P0171 and P0174:

- Fuel Sys: Closed
- Calc Load: 28.2%
ECT: 190 F
STFT B1: +12.5%
LTFT B1: +27.3%
STFT B2: +12.5%
LTFT B2: +25%
RPM: 717
Speed: 9 mph
Spark Adv: 12.5
IAT: 69.8 F
MAF: 4.92 g/s
TPS: 18.4%
O2S B1S1: 0.405 V
STFT B1S1: 12.5%
O2S B1S2: 0.260 V
O2S B2S1: 0.490 V
STFT B2S1: 12.5%
O2S B2S2: 0.205 V

 

Sounds like a bad TPS since both left and right trims are acting the same.

 

It's either insufficient fuel or unmetered air after the MAF. Nothing wrong with the TPS data provided.

My suggestion in post #5 is repeated.

Afterthought - Make sure that someone didn't fill the tank with E85....