Glowplug Harness Replacement
From Fusselman.org
I don't usually break out posts like this (this goes with Oh it Glows) but this could get a bit lengthy.
Recap: A few months (ok, like 16) ago, I started throwing a check engine light for a glowplug failure. At that point, I replaced one plug, and was getting intermittent codes for a second plug failing, though the plug tested fine. I wasn't really well versed in the glow system beyond the plugs themselves at that point, and the car seemed to start and run fine, even with an occasional CEL.
As the weather started getting colder this year (October 2009), I was getting harder starts and a healthy bit of smoke when it was especially brisk. I eventually ordered a replacement glow plug harness (P/N 038971220C) off of eBay (about $60 shipped). I was relieved to find out that my car (as a "late '02") has the 4-wire harness with connector, such that no splicing is needed (the older, two wire harnesses were spliced into one of the main engine harnesses).
After reading a bit on the Internets, I discovered that there were three "procedures" people were touting for replacing the harness. I'd note here that all three choices only exist where the "boot" part of the harness (the big sparkplug-boot looking thing that connects to the plugs) is the point of failure, which it mostly seems to be. Something about using spark-plug style connectors for huge current at 12 volts isn't so hot.
Anyhow, the three mechanisms:
- Cut off the "boot" and splice the new one on
- I hate splicing wires;
- Factoid: The "VW Way" of field splicing wires (like at a dealership) is crimping, not soldering; I chalk this up to the fact that a good solder joint is better, but a bad solder joint is a whole lot worse than a crimp. Crimps are predictable, consistent and just about anyone can do them acceptably.
- Remove the battery tray, airbox, etc, unwind a dozen harnesses and replace the OE harness "right"
- I hate extra work whereby nothing is actually gained in terms of functionality
- Cut the "boot" off of the OE harness and find your own way to get the new harness to the mating connector, located inside the main "wiring elbow", on the engine side of the firewall, adjacent to the steering wheel.
- This was totally my option.
In the end, I ran the new harness around the engine (following some other harnessing that headed back towards the firewall) and then down the firewall itself, into a knockout on the side of the wiring elbow housing. I did have to remove the air box to get the conduit open (the harness connector is actually inside the elbow), but that's just 3 bolts.
Then, the real fun started...
While I had the harness off, I figured I'd take stock of the glow plugs themselves, and make sure they were all looking healthy (With an ohm meter). The Bentley states that they're supposed to draw 6 amps nominal. I understand that they're nichrome and as such are an inductive load, so this isnt perfect but it will definitely show a bad plug. Ohms law shows that 1 ohm at one volt is 1 amp (thus 6 amps at 12 volts = 2 ohms). On an aside, I had a fancy TeX formula all worked out here, but it looks like I dont have support complied. Maybe next time.
Point is, if the plugs read <= two ohms, they're drawing at least the requisite 6 amps and are good. Needless to say, one of mine did not. The leftmost plug was reading "open circuit"... Not happy. Even less happy as I had none on hand, and the car was in bits, so as I couldn't go get one. The Advance on Saddle Creek had one in stock (6 actually), and I conscripted my friend John to take me down there. [Thanks!]. On the upside, this particular plug was easy to install, as there's no fuel lines obstructing it from above, making it easy to install and torque.
All put back together, it's the first time in a year and a half (and over 10k miles) that I've been without a CEL. Gotta love it. Now, I'm almost motivated to do some other random fixes that I've been holding out on. It's funny how one little orange light (or the lack thereof) determines how you feel about your car...
