Not wanting to permanently wire into the ECU, I made up a breakout strip
from a junkyard ECU Plug and Socket.
This gets all of the inputs and outputs up readily accessible to make
whatever readings are appropriate.
 This unit plugs in between the ECU and the ECU Harness.
I can then easily connect an oscilloscope or meter to monitor the voltages
and waveforms of the ECU's inputs and outputs.
Also when disconnected from the ECU, I can measure the resistances of the
Injectors, AFM, Etc.
Photo: http://www.dakotacom.net~nhansen/neal/vw_tester.htm
Parts are:
 Plug from Junkyard ECU, Socket also from Junkyard VW,
Terminal strips, multi conductor cable, and a  piece of board. and does not
interfere with the running of the engine.
My personal feeling is that I don't need any more bells and whistles on my
dash. But when it isn't running right I want an easy way to find out what
gives.
Neal