How long and easy is it to rebuild oil pump on 94 grand caravan 3.8l

Don't bother. Replace the unit.
3.0 liter
The oil pump assembly used on this engine is mounted at the front of the crankshaft. The oil pump also retains the crankshaft front oil seal.

1. Remove the accessory drive belts.
2. Remove the timing belt cover and timing belt. Refer to the timing belt removal and installation procedures in this section.
3. Remove the crankshaft sprocket.
4. Remove the oil pump mounting bolts (5), and remove oil pump assembly. Mark mounting bolts for proper installation during reassembly.

1. Clean the oil pump and engine block gasket surfaces thoroughly.
2. Position a new gasket on pump assembly and install on cylinder block. Make sure correct length bolts are in proper locations and tighten all bolts to 10 ft. lbs. (14 Nm).
3. Install the crankshaft sprocket and timing belt. Recheck engine timing marks.
4. Install the timing belt covers. For more details, refer to the timing belt cover installation procedures.
5. Install the accessory drive belts.
6. Refill the crankcase and start the engine.
7. Check for correct engine oil pressure and for any oil leakage.

1. Disconnect the negative battery cable. Remove the dipstick.
2. Raise the vehicle and support safely. Drain the oil and remove the oil pan.
3. Remove the oil pickup.
4. Remove the chain case cover.
5. Disassemble the oil pump as required.

1. Assemble the pump. Tighten the cover screws to 10 ft. lbs. (14 Nm).
2. Prime the oil pump by filling the rotor cavity with fresh oil and turning the rotors until oil comes out the pressure port. Repeat a few times until no air bubbles are present.
3. Install the chain case cover.
4. Clean out the oil pickup or replace as required. Replace the oil pickup O-ring and install the pickup to the pump.
5. Install the oil pan.
6. Install the dipstick. Fill the engine with the proper amount of oil.
7. Connect the negative battery cable and check the oil pressure. Check for any oil leaks.