No long-term fuel trim numbers

[yazuki101]

Hello,

I am currently working on my wife's 2005 Sport Trac 4.0L SOHC. I am trying to read the long-term fuel trim values on my scan tool, but the PIDs do not seem to register any values. The short-term trim, engine coolant temp, and any other PID seems to be working fine, but there is no value for the long-term trim. Here is a picture of my scan tool display during a live data session:

As I said previously, the ST fuel trim appears to be working fine. It fluctuates between ~ 2 and -2. It just happened that SFT1 was at 0 when I took the picture. However, the LTFT1 & 2 never change.

Any advice on where to begin would be great. Here is a brief description of where I am now with the truck. After it began throwing lean codes (P0171 and 0174), I found a vacuum leak resulting from a loose hose clamp on the air intake hose, on the MAF side. After tightening it up, I found the truck to still be hard to start and idling rough when started, but no long throwing lean codes. I am assuming the continued poor performance is because I have not resent the PCM learned values yet, which I plan to do ASAP.

However, during this diagnoses phase I was unable to determine the LT trim using my scan tool, so I would like to get to the bottom of this, regardless of whether or not it has anything to do with my current problems.

Thank you

 

[yazuki101]

UPDATE

I reset the PCM with my scan tool and am now getting LT trim numbers. They are within the accepted range when RPMs climb (btw -10% and 10%), but when idling (650 to 700 RPM) they LT trim climbs to 25.

I am also getting a P0191 code now, which I understand to mean that the fuel pressure sensor is not performing properly. This is a new code that arose just before I repaired the vacuum leak on the air intake hose and has stuck around since.