No Oil Pressure

I just changed thge oil pump on my 97 ford expedition, and still there is no oil pressure, I had a head job done right before this problem, the truck run for abou a week and then the oil pump went, any ideas

Does it really have no pressure or could the oil pressure sensor be bad?

Did you pack the oil pump with grease before installing it? If not, it isn't primed. Standard procedure is to pack the pump with lithium grease first.

The oil pump may need greasing.