Just to be clear that we are talking about the same thing. The PTU (Power Transistor Unit) aka the ignitor, aka coil driver is not a sensor of any kind, it receives the signal from the ecu and changes it to the proper signal to fire the coil (as transistors do) and absorbing the heat and surge associated with firing a coil, when it craps out, you get no spark, sound about right?
These are a common point of failure as these cars age, I'd have a good look at my engine and chassis grounds, IIRC there is a chassis ground near the drivers headlight on the frame rail. If everything looks good I'd upgrade to the pathfinder unit
http://z31performance.com/forum/basic-r ... istor-unit