The CAN is needed to communicate with the cluster and ECU and key, if you have an immo delete you can run CANless, though you would still need the gateway to communicate properly with the ECU through VCDS.
I am running a common rail in a beettle, naked so to speak, no cluster and just using the original gauge for oil and charge lights. There is no room for the Jetta cluster, and no need either. I did retain the can for ECU speak, and the cluster wiring. I did have it hooked up at first for testing.
Cool build. I have been following it with much interest.
Common rails run so good in other cars it is almost addicting to want to put them in. I have a couple projects planned in my mind already.
Nice to see more CR swaps! You don't actually need the CAN gateway to communicate with the ECU via VCDS. My engine ECU is immo deleted, and has no other modules present. The CAN lines from the ECU do nothing but go directly to the OBDII port CAN pins, and VCDS works perfectly.
So no gateway, or anything other than the ECU is needed to run the CR engine and use VCDS. However, if you want to make use of the CAN system for the cluster etc, obviously more is needed. I have a cheap bluetooth OBDII adapter plugged in day to day, and read boost, EGT's, rail pressure, etc. That has also never given me issue despite the direct connection to the ECU.
For the instrument cluster, I kept the vehicles stock ECU for the time being. Water temp is given by the stock water temp sensor being plumbed into the cooling system, oil temp/level bolted right into the AWM oil pan I used, and RPM is given by a 60/2 reluctor wheel mounted behind the crank damper with the stock (2.7t) VR pickup mounted there. The TDI ECU uses it's original Hall Effect sensor at the rear of the crank.
I'm still working on a cleaner solution. I have a Teensy and CAN transceiver installed so I can pick up data from the bus, but I'm still sorting through what I've collected. As time allows I'll finish up that part of the project, eliminating the extra ECU and cleaning up my setup a good bit. In the meantime, I do have 2 OBDII ports. One for the TDI's ECU, the other for all the other modules in the car. The stock ECU is still accessible, and throws an impressive amount of codes, lol.