I'm having a problem with my brakes on my 95 F-250 diesel where when the engine is idling, I have no power brakes. I have checked the hoses and don't find any leaks. I don't know if it's the vacuum pump or the booster so I'm trying to find out how much vacuum the pump should be producing. I haven't checked it with a vacuum guage as yet but I understand that on a gas engine, the vacuum is around 15 inches. Is it the same for a diesel vacuum pump? Thank you.