Where is the crank shaft sensor on your 1990 Chevy silverado?

Chevy did not USE a CRANKSHAFT sensor on there engines in 1990. It don't have 1

If it's not firing, Then the most common problem would be the ignition MODULE in the distributor. Could also be the pick-up coil / poll piece in the distributor. Check COIL WIRE, mAY EVEN BE THE COIL ITSELF. If you don't find your problem in these areas Then please ask your question again. If you have bad plug wires it can also BURN a hole in the rotor button and cause it not to fire.