I have a family member that is look at buying a 08 ford 6.4 an he said when you kill it has like two short burst of air. he said it sounds like an air dryer on a big rig when it builds so much it just pops for just a second he said that's what it sounds an he as an 08 one ton that doesn't do it any help would be great

 

Its the mechanical portion of the VGT. On the 6.0 the turbo had a cylinoid that controled the plate in the turbo and it would go bad causing no noticable problems or sounds other than a lack of full boost at take off. On the 6.4 they modified the VGT by loosing the cylinoid and replacing it with a mechanical system thats controled by the computer. When it starts going out it usualy will get sticky and stay opened until the motor shuts off and the waste gate releases the back preassure. Its not too hard to fix but it is costly.