Hey there! I have 93' 3-door 2WD XJ with 2.5L petrol engine and manual gear box.

In the near future I'm planning on swapping engine for BMW's 3.0L diesel M57. And since its 2WD I'm thinking of full swap with BMW's gearbox too.

So, here is my questions:

1. Is it possible to fully delete XJ's ECU and still making speedometer work? (From what I observed, my speedometer only works with ECU connected to engine wiring. With unconnected ECU it lays flat)
2. Is ECU needed for car to works properly? I'm mean like radio, light or anything besides engine? From my tests everything works just fine but maybe there is something I missed.
3. Any ideas how to convert any other gearbox so it can work with XJ's clusters?

Thanks in advance!

 

You have a big project. Yes, your ECU runs the speedometer on your 93. If you delete it, the cluster won't work. The ECU also runs the check engine light and possibly the fuel gauge. You can run the rest of the car without it, but you'll have dummy lights on.
You cannot easily convert the BMW gearbox signal. The best fix is to ditch the Jeep cluster entirely. Use a standalone speedometer that gets its signal from a new sensor on the BMW transmission or from the rear axle.