What info. I have found tells me a specific scan tool would be needed to check ecm that feeds a pulse width through the alt. exciter wire and checks instrument electronic circuit that controls ecm.
Most likely you can take a look at that with any old oscilloscope and monitor the pulse width and determine if it follows a set pattern or is all over the place.
I just bought a $60 hand held scope on Ebay from China for stuff like that and it's pretty neat.