My car was working fine, BB engine just a few years old and always run fine and maintained. I changed oil & filter with a Napa 51515 filter, pressure normal for about 30 miles then zero pressure on mechanical gauge. I check the drive gear and it was fine, removed valve in pump on BB and it was fine, no grit in there. Still zero pressure. I tried a new filter and pressure came right up, nd has been fine for years now. Bad filter somehow. Try that first and see.