Where is the oil pump located on a 92 jeep 4.0L 6 cylinder?

ALL OIL PUMPS are inside the pan, at the bottom of the engine. You'll need to remove the pan to get to the oil pump. But you should know that they seldom go bad. Amost ALWAYS, low oil pressure is the result of worn main and/or rod bearings. If you are having oil pressure problems, immediately change the filter only, check and top off the crankcase. BUY a QUALITY filter, not the same brand you are using. A certain brand is known to have poorly chosen materials in the construction and they will fail, eliminating oil pressure to the engine on a random basis. Paying extra for a good filter will never add up to the expense of a ruined engine, it's no savings if you saved $5 on a filter and paid $1500 to repair it. If the pressure is not dangerously low, but you want to improve it, use a teflon based oil additive as they will pump up the pressure 15 to 20 pounds. Keep in mind that 20 pounds of oil pressure on the gauge at idle is normal for many cars when warm.