Replacing PD Injectors Wiring in 125TDI engine.

[Greg Roles]

Well I spent all this afternoon fitting the supposed "improved" injector loom I got my brother to send me from the UK.



In a nutshell, the product code shown here isn't an exact match, and this arvo was one of my more "trepidous" efforts.



Even though it came from a VW dealer, it appears to me that it is an Audi A4 2.0 TDI specific part, and there were several differences. I got it to fit, and more amazingly, to work first go, but even though I took a video of the process, this isn't something I recommend people try for themselves, certainly not unless you can get an exact match part.

The differences were the actual injector plug ends, the wiring colours, the plug key-ing, and the actual plug pin orientation. I had to swap the newer loom injector plugs back to the old version ( the blade connector was identical, just the holder was different ) and the wiring colours were *close* but certainly not the same, and I spent quite some time tracing wires and working out what the heck was what - and then checked it again - quite nerve-wracking to be messing with the injection loom when it's dogey already.



On that, whilst the old wires did indeed look like the had sat in oil for 80 thousand kms, there was no sign of cracking, and I couldn't get the old loom insulation to crack, it was harder, but not so much that it would break just yet. The colours had definately faded, and the newer injector wire looks a little beefier, but both said 200 degree C on the insulation, and it's a definate feel good to have new wires in there.

The glowplug wires and plug ends were identical so that part was easy.



The keying in the new loom plug was a bit different, and I had to take to the new plug with the dremel to make it fit. The old plug had a key at 2 o'clock and 4 o'clock, whereas the new one was missing 2 o'clock, and had 10 o'clock instead. Not anymore.



Finally the most nerve wracking bit was injector 3 and 4 had their plug pin output reversed on the new loom, so I took a chance and changed the two plug pins around to match the old loom, and it's odd that all the rest of the plug wiring was pretty much identical. The old loom did have two injector earth pins ( two injector earths into each ) whereas the new loom only had one ( all four into one ), but I didn't see that as much of a problem, and perhaps this is the "improvement" in that there is only one earth running to the plug, instead of four on the old setup - less chance of a short?

I sat in the car, held my breath, turned the key, and it ran just fine. Went for a drive and so far so good, all as per normal. Pics to follow, tomorrow probably, need to get them off the new camera I'm still getting my head around.

[Greg Roles]

The old plug vs what came on the "new" loom, the internal spades were the same, so I just swapped them back into the old plug housing.

[Transporter]

Nice work Greg.
I was always suspicious but never said that and am wondering if the failed (cracked) insulation has anything to do with the oil quality (read it as "worn out" - old oil, chemically contaminated after some additives were worn out). It would be interesting to know, if the injector failure was on any car with 7,500km/6 months oil changes. I know that some will jump on and say, that they had an UOA done and the oil was good after 15,000km, but there are many diesels in US that had an UOA done and camshafts were worn out at 80,000km. I wonder if, VW had done UOA when they replaced the injectors or even looked at this possibility.

Do you want to start a new thread "Replacing the wiring loom in 125kW PDTDI" ? I can move the above posts there or you post a new thread and will delete the above. Could also link this thread to the new one.

Cheers, Good work.

[GoLfMan]

you are a braver man than I! Good work!

[jazd]

What exactly is the issue with the old loom? Does the insulation break down and produce shorts? Does this in turn kill the injectors or are they separate issues?

[Greg Roles]

That my friend is the million dollar question. The very fact that VAG replace both to try and eliminate the problem suggests either can cause the failure, and that even they don't really know.

Certainly what I found yesterday, is that the old loom insulation, whilst obviously faded, harder and at least three years of oil baths old, didn't crumble apart in my hands all Egyptian mummy like, which is what I half expected. Transporter may be onto something, as I do the 7500 oil and filter changes ( the cams looked in great shape, no lip at all ) and my car runs a lot cooler these days, the oil as well. I would expect the insulation to potentially break down due more to the heat cycling, and the fact all my efforts have been to reduce the thermal load on the engine may be part of the factor in why my old loom was pretty darn good. Could be just plain luck too, who knows.....

[PeDiES]

vw mostly replace the loom i think because when you use the genuine tool to remove the plugs they tend to shatter due to heat making them brittle.

[Umai Naa!!]

Spot-on. Not fun fishing bits of plastic out of the cylinder head.

Same goes for the big round cun... *ahem* connector at th end of the cylinder head. There's a neat tool for getting all of that mess undone as well.

[Greg Roles]

[Greg Roles]

vw mostly replace the loom i think because when you use the genuine tool to remove the plugs they tend to shatter due to heat making them brittle.

In all seriousness, removing the plugs is indeed a tricky task, and even though I worked out how to disconnect them eventually, I still can't fathom exactly how they are meant to unclip!