Chasing and exhaust leak that preventing my from getting my tuner finished. 08 Sierra Denali w/ 175k miles, 6.2, ls9 cam, 1.75 stainless headers, 3" stainless y pipe. Can't find even a trace of it at idle even using a hose as a stethoscope. Exhaust shop had no luck either. Not there at idle but can see it intermittently under heavy load in long term fuel trim and hear feel it under drivers floor board. Almost as if it only leaks when engine torques over against motor mounts. Any body seen anything like this before?

 

Are your motor mounts in good shape? I'd imagine at that mileage they could stand to be replaced if they have not been already.

 

Did they try a smoke test?

Like putting a smoke machine into the rear rail pipe and pumping the exhaust up with smoke to see all the tiny leaks.

 

Didn't do a smoke test but did find out the drivers side motor mount is trashed. Engine lifts a good ways under load.

 

Brake stall it with someone checking for leaks...

Sounds like you probably found the culprit though. Time for some solid mounts.

 

Made the motors mount "solid" with some plate welded on both sides, resealed the band clamps and its been leak free ever since