Tested the pump alone: 0-80 PSI instantly, 80-5 PSI in 5-6 seconds. Bad check valve? Pressure does not appear to leave via the EVAP. So I am not sure what I am hearing in the engine. The leak down does change with the temp of the engine. It is almost instantly when hot and slower when cold. I am installing an external check valve as the pump works fine and is only a year old. I own chevy, ford, toyota, and VW. This truck is the easiest to work on, but costs the most keep on the road.