Sensor help

I'm hoping someone in here can help me identify a sensor I busted off pulling out my engine last night.
It's a 89 4.0, the sensor is located at the bottom of the block drivers
side right above the oil pan in the block itself. it's about the size of my thumb.

I'm fairly sure I need this to start my engine today so I'd appreciate any help.

knock sensor it will run without it however the engine may ping

thanks I'll get a new one at the pull a part yard

It is not needed to start or run the Jeep. I have run 4 years with out one, so has 5-90.

It retards timing advance through the ECU when it signals the ECU that it senses an engine knock, like under heavy trailer towing load up hill in the wrong gear.