2002 F150 5.4L 4x4 Screw - 186K miles

1. Regarding the P1131. Found the following comment on the forum:
Before suspecting the HO2S, the wire connection to the sensor should be checked first. Examine the wires for chafing. Then inspect the connector on the sensor for moisture or damage to the pins. Because the signal voltage is very low (less than 1 volt) the connection is sensitive to damp or poor connection. The heating voltage and current should also be checked and these connections should be clean and bright.

Question: Where exactly is this sensor and the wire connection?

2. Prior to this, the Truck was also switching A/C to defrost. In checking the various vacuum lines, over by the battery area, I found the black line shown in pic 1 below (see red square) not connected to anything. It is in the same harness as the orange and green lines. I did not see anywhere to connect it and was unable to trace to the other end.
You can see another angle of this line in pic 3 with a yellow arrow pointing to it.

Question: Does it actually connect to something?



Long Saga Version
A/C has been intermittently switching to defrost for about two months. Codes P0171 and P0174 just recently appeared. I checked various vacuum lines and did not find an obvious culprit but did replace three of the "foamy" connection hoses that were not in the best of shape. They look really bad in pic 2 but most of that damage came while getting them off. Replaced with some pieces of fuel line hose shown in pics 3 & 4 below (see red squares).
Note: Yellow arrow in pic 3 is the vacuum line shown in pic 1.











I had already replaced four COPs over the past 1-3 years, so I decided to go ahead and replace the remaining four while working on this vacuum leak issue.
#7 was a pain. I was able to get it off without removing the fuel rail but ended up having to remove to get the new COP back in. Then on top of that, #5 COP connector retaining clip broke so I wrapped the COP-side connector with electrical tape, slid on the connector and put a zip tie on it.
Note: All replacement COPs are Ford dealer Motorcrafts (yes...ouch$$).

I also cleaned the MAF sensor. I did not take the sensor itself out. Just sprayed it, while installed, with CRC MAF Sensor cleaner once I had the whole air duct assembly out.

Put everything back together. Start the truck and it idles rough. Take it for a spin and engine continues a bit rough. Doesn't break down or hesitate on hard acceleration but just runs a bit rough. After about 3 miles, gets a bit worse and throws codes P0174 and P1131. Connections and hoses I checked looked good.
The elbow on the back of the throttle body has never been replaced but it feels like it is still in good shape.

Thanks for any suggestions.

 

in your very first picture "by the battery" your hand appears to be on the vacuum lines attached to the 4x4 vac solenoids. I'll take a look in my truck tomorrow to see if I can locate your stray line and attach a photo if i find a home for it.

As for your trouble codes, a quick google search lead me to believe your vac leak is one cause but so is a dirty MAF sensor. Have you looked at that?

There are a few other guys who may have better answers for you, be patient someone will respond

 

Thanks 1972-2003f150. That would be much appreciated.

Regarding the MAF sensor, yes I did clean it. Thanks for bringing that up. I'll edit the original post to include that since it is key info as well.

 

Work has been too crazy and have not had a chance to update. The rough idle after replacing four COPS was solved the next day. It was a loose injector connector on Bank 1 side.

Not sure what was throwing the P1131 but it is gone now.
What's left now are the P0171 and P0174 codes.

Let's go back to my original question on the black wire I found while checking for vacuum leaks.
Please look at the first pic and description. What is this wire and should it be connected to something?

Thanks,

 

I took some photos of my 2002 FX4.

 

Did you every get to the bottom of the Po171 and Po 174 codes?? My 2002 4.6l is doing now