In the spirit of, "I bet someone else has done this..."

I noticed in December that my Excursion was showing a P0374 code - an issue with the #4 glow plug - but hadn't yet triggered the CEL. I made a note to fix it and we headed to FL for the winter in my wife's car. We got back just in time for our annual Memorial Day trip to Moab, and the truck did great towing my 4Runner through the Rockies, but the code was still present. After we got back, it did trigger the CEL, and now the code was showing up as both a P0374 in the PCM section, and P0374-C in the OBD section, which I assume is what triggered the light.

I assumed the #4 glow plug was bad, so I ordered four from Riff Raff, planning to change all the ones on the driver's side. After swapping #4 this weekend, and deciding not to fix what wasn't broke and leaving the other three alone, I buttoned the thing back up, cleared the codes and... it came right back. Several times. I was not amused. I left it for the night with a plan to ohm out the circuit from the GPCM back, and to replace the GPCM if the circuit checked good.

The next morning I found the problem in five minutes. I had installed a fuel pressure gauge three years ago, and the loom around the glow plug harness wasn't quite long enough to protect the wires from rubbing against the side of the sensor. In the photo below, I have the sensor wire unplugged, and the black GPCM connector disconnected and peeled back to the right, showing the "underside" of the wires when normally connected. You can see in the center circle that the insulation has just barely been chaffed to the wire, and I've marked in the circle on the left where it would touch the metal sensor housing in normal operation.


I briefly thought about replacing the whole harness, but figured what that $100 would really buy me was a bunch of splices. So I fixed it the poor man's way. A short piece of electrical tape around the chaffed wire, and extending the loom a bit to protect the whole bundle.





That did the trick. Once the code was cleared it didn't come back.

In hindsight, I should have seen this as a problem when I installed the fuel pressure sensor, and should have checked the circuit before ordering parts. I did learn something about checking the wiring on these, though: "Checking" means both "test" and "inspect". Had I not seen the chaffing and just hooked up a meter or test light, the circuit would have tested fine, and I'd have been the proud owner of a scarce and expensive GPCM that didn't fix the problem.

You guys have helped me a lot over the years, and you know so much that I don't contribute much. This seemed like a good opportunity to reinforce what we all know, and many of us sometimes ignore, anyway: The correct order when working on anything is Prevent, Inspect, Test, then Order (parts).

Mark

 

I've got a new Fuel Pressure Sensor to install when the Wx cools enough for me to work outside under the Shade Tree.

This is a Warning to me, to be super careful with that wiring harness and inspect everything up close.

 

Things rubbing together is not always a good thing, mmm'kay?

 

My work here is done. I did look around to see if moving the sensor would help, but it's actually in a good spot that required minimal plumbing.

So I've heard.

Mark

 

somehow I just new he was going to say something... Bro you are like a special needs family member... always coming up with something inappropriate that makes me laugh my *** off.

 

We all contribute in our own way sir. Mine is in the form of non-value-adding comments.

 

I don't know about that I have found several of your posts to be quite informitive... even the ones that do not discuss sex in some fashion

 

So the ones that do discuss sex are informative for you eh? Interesting...