If you plunger gets stuck at the bottom you will have to great a oil pressure. If it gets stuck in the middle (more common) you will have very low oil pressure. I would suspect you may have a cracked pickup tube and a scored oil filter adaptor (If its new just remove the plunger and clean). You should also be able to see the plunger from where the oil filter screws on. You can use a small screwdriver to pry it back a 1/4" and then it should slide out. If it doesnt well that may have been the issue.