pex plugged?

Try this mystery.
Car runs fine on d2. Switch to grease and filter gauge goes to 25 in. Of vac and car dies no fuel. Changed filters pulled oil thru all lines with mighty vac fine. Took line off pex at filter stuck it in a jug runs fine. Drained tank no crap in bottom. Copper element spotless like new no poly. Blew out line 150 psi both directions put it all back together primed lines same thing. Ran a temp hose front to back hose on hose style threaded a pu tube and fitting through hatch. Works fine now. How can the pex flow air but not grease. Any thoughts on this mystery. Chunk of poly from cap? Permatex from the hatch? The air should have blasted any junk out of the line.Dose pex collapse? Im stumped