Just finished my motor swap with a used engine. Start the engine oil pressure hits 40 then falls to 0. I checked the lifters and they are dry. I didn't replace the pump on the engine because I primed the engine before I put it back together and it seemed fine
Should I replace the pump? Anything I can check first? I also put a new oil pressure sender on before I installed the engine and deleted the oil cooler. Thanks

 

I would use a mechanical gauge to be positive before you pull anything apart. It usually take a few seconds to pump the lifters up and a bit more to get oil up top (and some rpm for my engine).