I know this isn't what this crowd's expertise is in but I figured I'd pick a feew brains.
My buddy has an 01 Siverado with a DMAX. He tells me that if he romps on the trottle a little he hears a sound that he explains is like a burst hissing air compressor line. He told me that it will only do it when the truck is in gear. He said he checked all the lines and hoses with no leaks. The only performance drop he noticed was a slight drop in power when towing.
Now my best guess not being a diesel expert is a waste gate going south. But wouldn't that be the opposite symptom? (A loud hiss when letting off the throttle)
Any input with this would be cool, he keeps coming to me like I'm the Diesel expert
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What you describe is exactly what an intake leak sounds like on a turbocharged engine. It will only leak under boost (ie in gear, under load). Some turbo intake leaks can be difficult to find, because they only open up under load. If you're lucky, you can get enough boost up power braking it (if it's an AT) to quickly hear and ascertain the location -- you can't power brake an AT very long, they overheat quickly.
I recall a Volvo turbo I had to find an intake air leak on -- it was a cracked weld on the intake!
The most common places are, of course, where hoses transition. Although I've been under the hood of a Duramax, it's been a couple of years and I don't recall the layout, but look at soft parts and clamps first. If that doesn't yield results, you may need to simulate a dyno on a lift (or use a real dyno). Brakes don't like this. Do your diagnosis quickly.
Power loss and more smoke than normal, plus the hissing, are the symptoms of lost boost. Also the symptoms of a failing turbo, and also of an exhaust leak between the head and turbo (but the sound is less like hissing and more pulsed, like the exhaust it is). Although, now that I think of it, the modern engine management systems probably compensate low boost pressure better than the old systems, so maybe just lost power and noise, not more smoke.
Heck, Google "Duramax turbo air leak" or something like that, if it's a common problem or Q, maybe you'll learn something.
