No Spark

I have a 91 grand prix 3.1L that won't start. The motor cranks fine but no spark. Here is what I have done so far: I replaced the plugs and wires, tested the coils (they were good), replaced the ICM (this tested bad), tested the crankshaft position sensor (this tested good, the manual said that this plugged into the ICM and that I could just test by measuring voltage accross the harness terminals???), finally I replaced the ECM. Still no spark. I am getting power to the ICM and the ground circuit is OK. I have also checked all fuses. I do not know of anything else to test. Any ideas? Thanks alot.

Tom

OK, I am trying to confirm that I have tested the crankshaft position sensor properly. I believe that it plugs directly into the igniton control module and that I can test it at the plug by measuring the voltage across the terminals while cranking the motor. I actually did this and I was getting a reading that fluctuated between 200 and 500 millivolts. However at the parts store yesterday someone told me that it did not plug into the ICM on these models. It is difficult for me to trace the wires back from where I am assuming the CPS plugs into the ICM. Does anyone know where the CPS is located on a 91 grand prix 3.1L? And am I testing it properly?
Thanks alot,
Tom

here's a link to Auto-Zone's website repair info. The first is general info about how the system works, the second is diagnosis info. I hope this helps.

http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/0e/c6/a5/0900823d800ec6a5.jsp

http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/0e/c6/b0/0900823d800ec6b0.jsp

Thanks for pointing me in the right direction. It did help in regards to the crankshaft position sensor. I am still pretty much back where I started from with no spark.