TDI install retrospective: ECU, dashpod and Sensors

Continuing, or should I say completing, the process of back-documenting what I did to put a TDI engine into an old (1972) air-cooled VW bus. Today I cover whatever is left of the install that I didn't already cover. I had intended to focus this post on the ECU, dashpod and sensors, but most of that stuff was covered the last time.

ECU

ECU image nicked from eBay

Like any modern car, the ECU is the brain of the outfit. It's rather small, for what it does, measuring around an inch thick and around 4 x 6 inches rectangular. There are 2 large rectangular plugs that slide and then lock in. One of them is for the harness that goes to the engine. The other does everything else. The engine harness is the more important of the two, but only just barely. I was able to leave that harness almost completely untouched. I just unwound some tape here and there, but otherwise, it routed like the stock TDI implementation. I left the AC compressor plug dangling where the AC compressor would go, but everything else plugs in. Because of the ECU location in the spare tire well, the harness did not need to get extended at all.

The other (non-engine) harness gets interesting. This is where the majority of your sleuthing will take place. Many of the wires go to the fuse box, and many of those fuses are not needed for our implementation. I chose to leave the wires from the ECU to fusebox alone. Instead, I pulled the fuses for the unused circuits and then removed the wire from the other side. This left less of a mess than had I left everything there, but also reduced the risk of removing something I had to put back... Which happened. Other wires go to the dashpod or the relay blocks. I can't really advise much more on this other than to take care as you decide whether a circuit is needed for your implementation or not before you cut it out. Kind of like that "measure twice, cut once" axiom.

Dashpod

TDI Beetle dashpod

I took measurements, and early-on thought about how I could retrofit a TDI dashpod into the bus dashboard. The VW Beetle dashpod is a single mostly-circular (shy of 270* of a 360* circle) face with a thick surround. It could not fit without some modifications to either the dashpod or the bus dashboard or both. I also own a Jetta of the same vintage and took measurements of that dashpod. I probably could have fit that, but then I would have had to re-think a few things, starting with the speed sensor. More importantly, the ECU and TDI fusebox were in the spare tire well 10 feet or more behind the driver seat. In order to get all of the signals to the dashpod, I would need to extend 30+ tiny wires and hope for no signal loss. Instead, I left the wires alone and buried the dashpod in the spare tire well. The engine will not operate without the dashpod wired in, by the way.

FuseBox and Relays

fuse box image nicked from "PopScreen"

As you work your way through the circuits you don't need, eventually you will work your way to the relays. You don't need many of them. Of course, you need the 109 power relay and the glow-plug relay, but as you remove the things you don't need (cooling system pre-warming glow plug circuit, for example), the support stuff falls off along the way. I have both the fusebox and the remaining relays, still in their respective relay holders, living in the spare tire well.

As I mentioned in the secondary electrical post, I will be re-visiting the wiring in the spare tire well as part of my seasonal readiness this Spring. I would like to re-run the wires from the front-to-back using a single cable as well, making the wiring seem more purposeful.

Idiot Lights
I mentioned that the original bus has 2 warning lights (well, 3 if you include the brake warning light). One says your engine is toast and the other says your electrical is fried. Not very useful, but they're better than nothing. The TDI has a few things worth warning you about too. First is a Check Engine Light (CEL), sourced from pin 24, it gets voltage when a code is thrown. Second is the glow-plug light. This will tell you when the engine is ready to start when it's cold. It will also flash at you when certain error conditions occur. This second reason makes the case to have something. Next is the coolant light. This lets you know when you're low on coolant and on the TDI cluster it flashes for some error conditions. Again, good to have. Last of interest are your charging system and oil pressure, just like the old bus had.

If you look back through the blog, you will not find any posts about this. Why? Well.. truth be told, I didn't do any of these. I run the UltraGauge and that alerts me of any code being thrown, so I don't need a CEL independently. I don't run the bus when it is cold, yet, so I don't need a glow plug light yet. When I do, I will tie into the glowplug circuit to light when it is energized. That's a cheap way of getting there. Others have tied into pin 40. For the coolant level warning, I will tie directly into the 2-prong sensor in the coolant bottle. Frankly, I probably should have done that a long time ago. The charging system could be a simple relay that sends a signal when the difference between the battery posts is below 12V. Alternatively, you can create a "real" alternator light by sending switched 12V to one side of a 12V bulb and the other side to the "exciter" terminal on the alternator (labelled D+ or L). The oil pressure is actually complicated because the TDI cluster determines whether the oil pressure is low for the engine speed. If you really want an independent oil pressure message, it might be worth getting an after market gauge. I haven't decided whether I want that or not. I like the simple dash I have now, though the UltraGause does not include oil pressure. So, this is a continuing risk, for now.

I hope these retrospectives were useful. I realize I neglected to re-iterate the deep details that appeared in the original posts. That seemed excessive. Instead, I focused on the big-picture things that worked, expecting interested readers to leverage the search function in the blog or to follow the links when I did it for you.

Prior related posts:
Preparation
Fuel System
Physical Mounting
Vacuum System
Air, Intercooler and Exhaust
Primary Electrical
Cooling
Secondary Electrical

Now that these retrospectives have been completed, I expect my postings to drop off for a while. I have a number of projects all starting up at once, so while I will be generating content, it will be a while before any of them reach a point of post-worthiness, much less align on the weekly cadence I've been on for the last 2 years.

As always, thanks for following along, and I'll get back to posting when there's something complete enough to write about. Peace, Love and Smiles-