Min TCU wiring for 82' e21 with M52TU and Auto transmission

[bimmeup02]

Hey all, I'm brand new here and have a question that I couldn't quite get answered in the search.

I have recently acquired a 1982 e21 (US spec) that had been previously converted, very poorly, to M52TU with a GM 5L40 Auto gearbox from a 2000 e39 528i. The car runs and drives, but whoever did the swap did not build a proper swap harness, instead they took the entire cockpit wiring harness and carried that over in a bundle on the passenger floor. As stated, the car runs and drives, so the engine harness was done correct...enough, but that's it.

Not only is this interior mess unsightly, but it's rather dangerous. Well, I am working to clean up this mess by removing everything but what is needed to run the car and make the transmission work. After I get this sorted out I'll take it one proper step further, I have purchased a proper swap harness for the e21/M52TU combo, but have not installed it just yet as I also have recently purchased a standalone ECU (DIY-EFI Core4 Speeduino) that will be installed permanently once the wiring is sorted. The ECU from DIY-EFI is a plug-n-play unit, I've already tested it out on this messy harness and it works fantastic...throttle response is amazing. I can blip the throttle 3x in the amount of time it takes for one stock rev. Anyway, I'll report on the results of the Speeduino unit at a later date, gotta get this transmission sorted first.

Additionally, I do plan to swap in a 6-speed gearbox in the not too distant future, but those are hard to find and/or expensive, and my job has me traveling very frequently, so until then I will need to make this slushbox work better than it does. One problem I can definitely see is that, since the gearbox has no sort of vehicle/wheel speed reference being sent to the TCU (no ABS in 1982) it shifts through all of the 5 gears by the time I reach about 30 mph (50 kph). Until just recently I could move the gear lever into the Sport position and shift gears manually, but in my attempts to clear out unneeded bits of the e39 wiring, I must have disturbed some wire(s) that the gearbox needs? I took great care to not remove anything associated with the Transmission Control Unit or the shifter, all harnesses are intact, and as far as I could find, the factory MS42 ECU did not play a role in the operation of the auto gearbox, but now I only get indications of sport mode, no actual shifts happen?

Anyone out there have any experience doing a similar M5x Auto swap into an e21 and care to help me parse out what little bit I need to make the gearbox work in Sport (manual) mode? I really don't care much about working in full auto mode unless there's an easy solution. I've read all sorts of info about Can-Bus inputs, and needing to program the TCU, but there's gotta be an easy way to make this box work in one mode or the other...WITHOUT needing ton of wires from the donor car.

So to sum it up, I have the proper M52TU Engine Harness and ECU, I have the Automatic Transmission and TCU along with it, but I also have the whole e39 front cockpit harness coiled up on the passenger floor, likely because the original swapper didn't want to deal with the EWS Delete and the work needed to trim down to the bare necessities of the cockpit wiring. Thanks in advance

[Jeroen]

Welcome here, out of my league though haha. BTW moved your posting to the Tech section.

Feel free to make a little presentation of yourself and your car in the owners gallery!