Hi Guys, this is a strange problem!
I have a 55 plate 2.0 TDCI Ghia 115ps (120,000 miles). During acceleration, when the turbo cuts in at about 2000rpm, I get a loud "hiss" from under the bonnet. It sounds like a lot of compressed air leaking out of somewhere.
I have checked as many pipes and clips that I can see under the bonnet and underneath with the under tray removed, but cannot find any evidence of leaks.
It has a new exhaust system and with the engine on tickover, block the tailpipe with a rag and it builds up a lot of pressure without any leaks.
The noise does not happen by just revving the engine while stationary, only when it is under acceleration load. There is no loss of power and the fuel consumption is not affected also no smoke from the exhaust.
The car is standard spec but I sound like a boy racer with a dump valve fitted but I only get the noise when I put my foot down, not on lift off.
Any suggestions would be welcome!