I have a 90 Cherokee with a 4.0l. When it gets to operating temp it starts knocking. What is going out? It sounds like it is deep inside the motor.

 

hopefully it's just the knock sensor?

 

oil level is ok? oil pressure is ok? try this, take a screwdriver, a long one, hold the handle to your ear and place the other end along the valve cover,while the engine is running, BE Careful, no loose clothing. do you hear the noise from up top? does it seem louder as you move down the cover. with the wheels blocked, go under and do the same to the oil pan and block if you can reach them. the noise will transfer down the screwdriver, just like a steth-i-scope[wrong spelling] this may point out where the noise is coming from. top end or bottom end. good luck.

 

Oil level is good, oil presure ok not great on the low side, maybe bad sending unit. Screwdriver trick gets louder on the low end but can hear from the top side.