I have a2013 tahoe 5.3 ls engine. blew it up. bought a used engine put a new timing chain, oil pump, pick up tube etc etc. My son put it all on and dropped the engine in. Problem is we cannot get any oil pressure. We filed it with oil and also tried filling the oil pump from the port on the side of the motor by the pump and turn it over and still cannot get oil pressure. what are we missing or doing wrong or what can we do. I need help this is our only vehicle I spent a ton of money putting this used engine in and still owe a ton of money on this car. we haven't been able to drive for 6 months help