1984 Chevy Cavalier fuel system

i work at a local automotive repair shop, and we are all stumped. we have never seen anything like this before. the 2.0 caviler we are working on, we had originally thought had a bad fuel pump. we have put in two new bosch fuel pumps now and are still having problems. we have tested the wires and even tho the fuel pump is supposed to have a 12 volt feed, we are recieving between between 8.30 volts and 9.27 volts. there are three wires runing to the sending unit, a tan wire, a red wire and a black wire. the red wire should be the power supply for the fuel pump, which is feeding the 8.30 to 9.27, the tan wire should be the fuel gauge wire, which is not reading any voltage, and the black wire is of course the ground. now i know that on this model, the power supply for the fuel pump is supposed to run threw the oil pressure sensor, and that if the oil pressure drops, it will cut power to the fuel pump and shut the car off, so i checked the oil and it was about a quart and a half low, so i added some and still no results. we have also tried applying a strait 12 volts from another battery to the female connection for the sending unit, and you can hear the fuel pump doing something, but when the fuel filter is disconnected there is no fuel being pumped threw the lines. i also think i should add that the sound the fuel pump is making is more of a quiet grinding rather than the typical sound of a fuel pump. we have also tried changing the fuel pump relay, which was sort of difficult to find since the chiltons manual list that an 84 caviler with a 2.0 had no fuel pump relay, and that changed nothing. the car will run if you spray starting fluid into the throttle body, so i'm thinking it has toeither be something in the computer or something in the wiring from the conector to the sending unit. but recently i have been swayed to beleve that it may also have something to do with the relay or conductor that the wires from the sending unit to the fuel pump are run off of. as i said earlier in the letter we are all stumped, and running out of ideas to try. PLEASE HELP!!!!