no rpm signal

I have a 1987 chevy iroc z28 with a 5.0l tuned port injection, has 52054 miles on it. IT will not start. I checked for spark and fuel , got nothing. Changed the module and coil still no spark or fuel. Put scan tool on and shows no rpm signal. I would like to know where does the rpm signal come from. all test say it should have a rpm signal to continue.
Thanks
Don s