Revenge of the 327

[Eric1971]

At some point in the last 2.5 years, I pulled all the KOEO and KOER codes and tracked down the errors and squashed them. One of them was the famous 327 "EGR valve position circuit below minimum voltage." I did my searching and reading here and replaced the DPFE sensor which made the error go away for about a year, then it came back two months ago. Since I had used a Duralast part, I got a new one under warranty, which lasted about a week. I then got the Motorcraft part with new wiring harness and installed that but it did not correct the error at all. This week I checked the voltage to the DPFE and it's reading a solid 5VDC. I'm not sure what to check next: IAC valve, EGR valve, vacuum lines? Note that there are currently no other codes and after every fix attempt, I do the whole process to clear codes and relearn. I don't see any symptoms other than maybe the exhaust smell, but not sure if it's more than it should since it's 25 years old and never failed an emissions test. Didn't get a test this year since it's now past 25 years and no longer required in metro Atlanta.

Advice is greatly appreciated!

 

[Eric1971]

Vref = 5.0V
SigRtn = 0.078V
DPFEGR = 0.084V

New DPFE hoses, good ones.

 

[Eric1971]

Oh FFS, I found the issue. I will resist deleting this post from embarrassment and leave it here so someone may hopefully learn from my mistake. The instructions that came with the new Motorcraft wiring harness were VERY specific on the wires, but either I got something turned upside down or had a moment of color blindness or I don't know what because I swapped the top and bottom wires. So while Vref sure was coming in reading 5.0V, it was connected to the DPFEGR wire of the sensor, and the 0.084V DPFEGR signal was going to the Vref connector, so what do you know, the voltage was low!

Apparently, the Duralast DPFE sensors (two of them) did actually go bad (1 year and 1 month, respectively) before I miswired the new harness. Let's hope the Motorcraft one lasts a nice long time.

 

[Eric1971]

Special thanks to @94xlt4WD here (code 327 (check engine light)) for inspiring me to check the wiring.

 

[410Fortune]

one thing I learned turning wrenches on these trucks for 20+ years now
First thing to check is the last thing you touched