Palio 1.2. Why is there no oil pressure?

Very low or no oil pressure reading does not necessarily mean the oil pump is not working and if you replaced the oil pump because of low oil pressure does not mean the original pump had necessarily failed. It may have but it may not have. Oil pressure is not created by the oil pump but by the resistance to oil flow. If you have very low resistance to flow you will get very low oil pressure no matter how well the oil pump is pumping. If you have a very worn engine, especially the bottom end main bearings and conrod bearings, tolerances increase very significantly, there is little resistance to flow and you will achieve very low oil pressure and metal parts will touch. Oil flow to the upper part of the engine may also suffer. If your engine is gummed up with oil sludge due to too few oil changes some oil passages may be blocked as well.