Has there ever been silicone based wax used on the vehicle? Even a minuscule amount of silicone, which can penetrate all the way to the base metal, can produce the problems you're getting. Unless a panel has been stripped all the way to bare metal, silicone contamination is difficult to remove. Also, oil in your compressed air, not water, can be a huge problem. If your compressor has some piston ring wear, it can be contaminating the air you're using for your spray gun. The air filters that use a roll of toilet paper are pretty effective at catching oil from a compressor. That's what we used on the air lines to the spray booth at a couple of body shops I've managed.

McMaster-Carr catalog reference: Part numbers 9841K91, 92, or 94, depending on the pipe size of the fittings.

www.mcmaster.com/catalog/130/1237/9841K91

Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!