S4000 Turbocharger surging
Turbocharger surging where one turbo speed increases and one decreases, a wave pattern in noted on Diasys recording. This can be a little as 50 rpm and up to 300 rpm. Air inlet temperatures before turbocharger increases, exhaust temperature before turbocharger increases. Engine de rate occurs. A partially blocked intercooler is the cause of this issue, in this case it was exhaust being drawn into the air cleaner