I have a 91 XJ that loses power steering after warming up and at low speeds, also getting some popping sound that I can't locate on the front left. Does not appear to be coming from the steering box. Fluid level is good in the power steering but does smell slightly burnt. Bad pump????

 

does the click happen when you turn the wheel back and forth while stopped or only when moving. Might be U-joint.

 

Both, I just put in a front locker and the u-joints seemed fine.