Hello friends. I've finally decided to seek help here as I'm not getting the same answers from any mechanics that I know personally. I have a 1988 Ford Falcon from Australia with a 250CI I6 motor. The motor was recently rebuilt with all new bearings & components including the oil pump. I've driven the vehicle around 400 miles after the rebuild and everything worked just fine. All of a sudden one day the oil pressure light flickered and went away. While driving the next day, the light turned on and stayed on, and I heard tapping noises from the engine. I stopped the vehicle as soon as I could. The next day, I installed a mechanical pressure gauge in place of the pressure switch and started the engine. There is zero oil pressure at idle, and goes up to around 5psi of pressure at higher RPM. I didn't revv it too hard. Tapping noises are from the top of the engine. I shut the engine off as soon as possible after checking for pressure. I have replaced the oil and oil filter since then, but I didn't think to inspect the old oil filter. The engine never ran low on oil as I constantly monitored it since the rebuild. I cannot take the vehicle back to the engine rebuilder because it's half way across the country as I moved since the rebuild. Please let me know what you all think the problem could be. Thank you.