deficiencies in Lubricacion Daihatsu Terios 2001

I request the favor help me with the following problem

a Daihatsu Terios 2001 began with a lubrication problem which consisted that when the engine was started with the vehicle on rise, it started badly and the oil pressure witness did not go out and sounded the engine badly with a small poured, the vehicle was left to leave it leaving it in low and it was possible to start well. Ultimamante The problem exists in any position of the vehicle.

The carter was removed and the Eceite shot was free, the front lid was removed, the pump was found with little wear, however, it was changed, the pipe-pump ducts, filter pump and filter to the butt were processed and were cleared; However, the problem persists.

What can be happening, what do I do ?????

Thank you very much for your collaboration if someone has the service manual of this car would thank you very much if you can send it to me.

If everything is clear, I check that the element that produces or activates the oil pump, is in good condition