no spark on my 93 lumina apv, tried everything i can think of new crank sensor, about 4 used ecm modules and tested all the wires for spark circuit , so i was wandering how to back probe cam sensor to make sure it is sending signal to the ecm any ideals?

I assume you have teh 3800 engine, as the 3100 has a distributor. IF you unhook the electrical plug, and hook an ohm meter to the two terminals on the cam sensor, as you crank the engine, your reading should fluctuate as the magnet passes the sensor.