I have a 95 Nissan truck with the KA24e 4 cylinder. I can drive the truck a few weeks with no problems. If I let it sit for a few weeks I have no oil pressue when cranked. I pull the oil pump and prime it, reinstall distributor, and I got oil pressure. The first time this happened I'd crank it daily with no problems just to make sure I had oil pressure. So I let it sit for about a month. The other day I need the truck to pull a trailer and again no oil pressure. Yanked the oil pump, primed, replaced and viola - oil pressure. So whats the deal?