I bought a 6.0 E450 Bus a few months ago. When i bought it it would crank but not start. I cleaned the IPR valve with wd40 and compressed air (Dieseltechron procedure) and it started right up. The problem is that the IPR valve keeps failing for some reason, bringing back the crank no start condition. I drive the bus for 4-500 miles and the problem reappears. Every time i get the valve out to clean it, the screen always look free of debris to me. I also replaced the gaskets and screen of the IPR in hope that would solve my problem but no change were noticed after the service. So my question is, is it possible that the valve is damaged and don't seat properly, or is it possible that debris can stil get in through the screen? Can i repair it or does it need to be replaced? Thank you for your answers.