p071/p0174

[explorer37]

I have a 98 xlt 4.0 2wd 176,000 miles (on the 3rd tranny). During cold weather the CEL comes on and it throws the P0171/P0174 codes. This started last winter and I replaced the MAF, IAC, EGR and some other sensors that i cant recall at the moment (all suggested by earlier 171/174 threads). I have also visually checked and replaced all the vaccum lines that I can find. The problem is that this only happens when it is lower than 40* F outside. I cleared the codes after replacing the MAF this past spring and the CEL did not come again until a few weeks ago with the same 171/174 codes. My code reader will provide freeze frame info. which i will provide. My question is: Is this most likely and Intake gasket problem or Fuel? I am leaning towards the IG but would like some others opinions. Here is the FF data:
Frame 1 174, 1115 RPM, CALC LOAD 57.2%, Coolant Temp 204*, ST FTRM 1 32.8%, LT FTRM 1 -73.5%, LT FTRM 1 13.2%, ST FTRM 2 29.6%, LT FTRM 2 11.7%, VEH SPEED 0mph Fuel sys. 1 closed, fuel sys. 2 n/a Thanks for any help.

[shorod]

The freeze frame data shows that the engine is warmed up at the time, so it apparently was driven recently. Does this seem accurate?

The fuel trim numbers are wild, if I recall correctly, anything more than 12 or 15% is considered extreme. Those numbers would indicate that bank 1 is trying to go WAAAY rich over the long term and bank 2 is trying to go lean.

-Rod

[explorer37]

Thanks Rod, Yes it has been driven, the CEL will come on either in the driveway before I put it in reverse or when I get to the stopsign at the end of the street (approx. 1/2 mile). so the vehicle is always stopped when the code is thrown, but the outside temp. always seems to be less than 40* Also there does not seem to be any performance related issues. It still drives fine and gets the same mpg as usual. I will recheck the FF numbers that I provided, if they are correct is it possible that I have a tempature sensor somewhere that would be telling the computer to richen or lean the fuel to the perspective banks?

[shorod]

You'll also want to determine if the DPFE was one of the "other sensors" that were replaced.

-Rod

[goodoldpapa]

Originally Posted by shorod

You'll also want to determine if the DPFE was one of the "other sensors" that were replaced.

-Rod

x2. My stepdaughter had her CEL on all the time. When We took to advance Auto, it was reading the same exact codes. Took it to a local mechanic and it turned out to be DPFE sensor. Replaced that and no CEL since.

[explorer37]

Thanks for the info., but I did replace the DPFE because a part of it had melted. Since the warmer or hotter weather has arrived no CEL...I am planning on replacing the Intake Gaskets soon, so we will see. Once again thanks for the info.