1994 Cadillac SLS

Engine Mechanical problem
1994 Cadillac SLS V8 Front Wheel Drive Automatic 178.00 miles

i am haveing issuse with my caddy I replaced the water pump temp sensor and thermostate and after three min the computer says car over heat and trys stalling the car out but unplug the temp sensor and it dont chock out. After about five min I stick my finger in the coolent spout and the water is still cold but the computer says over heat and shut engine off but the motor is not even warm I have check to see if the head wear cracked no anfreese in the coolent no smoke from the tail pipe no water from the tail pipe so im confused. Also the number 8 plug wire is not firing I can hold it with a screw driver in the boot of the plug and nothing I think its the coil pack on that but dont know