I have a 94 150 with the straight 6. Rebuilt the motor and now i have no oil pressure. Thought it was the sending unit replaced it still didn't change so i bought a mechanical gauge and it's only read bout 5-6 psi. already pulled the pump and checked it and ran with out the gauge hooked up and oil came out, put the gauge back on and still 5-6 psi. Is that spot where the sending unit goes even a pressure spot. any feedback would help out.

 

sounds like you left out a plug in a oil galley or a mis aligned bearing.

 

Could also be a defective oil pump right out of the box. Look for the loose plug or a block fracture or oil pasage blockage and try pressure testing the pump before you put it in - then you can trace where the pressure is going (if the pump's OK). Never install an oil pump dry - it can burn up by priming it from dry at even low RPM.