The Oxygen Sensor on a 1989 Cherokee 4.0L is on the exhaust pipe on the left side of the engine just below the exhaust manifold. You can see it from above but you must replace it from below. It is pretty easy to reach. I recently changed mine and it took only 10 minutes using an O2 sensor wrench.
Need a special socket. They are located in the exaust manifold(s).
It does not have a mass airflow sensor.
It is inside the distributor.
The oil sensor is located above the oil filter next to the distributor.
above the filter
Inside the distributor.
The cam sensor is inside the distributor.
The 1994 Jeep Grand Cherokee IAT sensor can be found attached to the air intake hose. The IAT sensor will be near the air filter box.
in a toilet
It is in the distributor.
It is the two wire sensor next to the thermostat housing.
The cam sensor should be located underneathe your distributor cap. That is the placement on my 98 Grand Cherokee and it should be located there as well on yours.