hearing strange sucking(?) noise when i let off accelerator to downshift in hard pull. dont hear it when i'm going through gears or giving it throttle, but if i'm pulling hard loaded into a hill, i hear it briefly (but noticeably) as i let off the pedal quickly to downshift. checked all the red and blue intake hoses, and everything seemed ok, but continue to hear sound. should i go back and check them again? could it be somethin in the CAC, or the wastegate in the turbo flapping?

 

What is the year & make of your truck & engine? The more info the better, has any work been done to it recently, etc

 

2000 frtlner classic, c12, no recent work

 

Just had my Turbo Gasket go out yesterday. Mine started 3 days ago making a sound only when it was winding out loaded above 1500 rps, and then when I let off the pedal and the Jakes would kick in.

When I let off of it it reminded me of a old farm tractor. When it started it was barley noticeable, but then it got louder each day and I could not find it, until yesterday.

Put my hand around the turbo gasket while running (BE Careful that dude is hot) and found the air leak.

Mine is a C-15 Cat.