I worked in the collision repair industry for 28 years. The only reason we ever used a pressure washer on a vehicle was when we wanted to remove paint from it. Your average water hose has more than enough pressure to remove bad paint, no reason to add another 1,700-3,600 PSI to really get things moving.
Get the vehicle wet first, keep it wet, use the proper soaps, and everything should rinse off with a gentle spray. Places like Chemical Guys are in business for a reason.
I'd also pass on the average black spray bomb. Chances are it's an alkyd enamel and it will eat into the exposed edges of the water base paint like paint remover.
My hands were shot and we were 3 years into water based paints when I got out of the business. Don't miss it at all !