"Hissing" during heavy acceleration

[chessy56]

I have a 2001 Duramax with ~85,000 miles. Last winter, I began noticing a "hissing" noise (like escaping exhaust), only under "heavy acceleration". I've checked the clamped joint between the exhaust pipe and turbo exhaust (roughly even with the exhaust manafold, right side of the engine). The joint does not show any signs of leakage. I have not as yet, attempted to crawl over the top of the engine to check the exit pipe at the turbocharger.

Has anyone experienced this before? Perhaps a loose exit pipe at the turbo? A tear in the gasket between the turbo and exhaust pipe? The turbo itself?

Any tips or assistance would be greatly appreciated! Thanks much.

"Chessy56"

[JohnC]

How about a leak on the intake side?

[Tutts]

Sounds like you are on the right track. I know that the PCV system can introduce oil into the turbo and associated piping, causing clamped joints to slip. Maybe this is occurring?

[Joe Duffiney]

Check the intercooler piping also. Some have reported the power steering hoses rubbing holes in the pipe down at the bottom drivers side.

[carco]

Your description makes me think first of a turbo pressurized line that has a loosened clamp a split hose or a cracked tube or intercooler. Block the wheels, set the park brake tightly, stand on the service brake, place trans in drive add throttle untill the noise occurs while a friend is under the hood listening for the leak. Be very carefull do not run over the friend, or garage wall. The person under hood needs to be carefull where hands and fingers are placed due to moving objects, say a finger cutting fan, skin cooking manifolds, and egr pipeing. You can feel for the air leaking after useing your ears to help locate the sound. bob.................

[chessy56]

Thanks for the tips guys-
The noise appears to be coming directly from the opposite side of the firewall, near the rear of the engine- perhaps from an exhaust manifold or from the area of the turbo itself! (Maybe the question of an input to the turbo might be first logical place to start looking). After pulling the exhaust pipe off of the tubo's discharge pipe, I find no oil around the clamped joint or, inside of the exhaust piping. The noise definitely seems to be either centered or, closer to the right side of the engine, but just on the other side of the firewall. I'll have a look at everything and get back with you all.

[The Lurch]

When my '01 GMC started to do the same thing, I panicked and sent it to the dealer. He noticed that the intercooler pipe (post intercooler) hasd a hole rubbed in it from the fule filter line. I took it off, and welded it with an aluminum welder, and the problem was solved. Obviously, when I put the pipe back on, I repositioned it so it would not happen again.
Good Luck!

[chessy56]

Finally- got off my dead butt and located the problem. Just as "the Lurch" mentioned, I too had a hole rubbed in my intercooler return pipe from constant contact with the fuel filter's inlet line. Too, I noticed additional rubbing on the oil dipstick tube and the front-most exhaust header mounting bolt. As long as the truck is in the shop for a different issue (first 3 of 5 blower fan speeds dead), I'm attempting to get this replaced under the extended warranty as well. If not, it's an easy fix.

Thanks for the tips guys....