so we had a car with coolant in a cylinder and i wanted to see if the FLS sensor would show anything in the cooling system that i could sync to spark , so i connected the FLS sensor hanging over the radiator connected to a pressure tester without the pump and in place of the pump , the FLSc sensor . synced to cylinder 5 spark because wires to cylinders 1-4 are buried and 5 was next -
           with igt pulses from the coil negative connector at the dlc and i get this .

a path from combustion to coolant that lines up with Cylinder 4 spark , every 720 degrees a pressure pulse and a vacuum pulse in between , kinda sorta looks like a running compression waveform .