strange one. so once it gets to 5000 rpm, it wont go above that, and soon as it gets to 5000 rpm, the boost drops to 0?? once once you slow down, and then speed up, im assuming it just repeats this? dump valve, , but youve changed it? wastegate gettin stuck open. youve dropped to standard boost, so is this happening, at a certain rpm, or a certain level of boost, for example, it always happens at 0.7 bar? or it always happens at 4500 rpm?