LOUD air leak under dash M931A2

[DocPA]

I have a 1990 931A2 that was a rebuild. I've found bad grounds, air lines crossed on the transfer case and some plugs not plugged in. BUT I have a loud air leak under the dash that starts at higher rpm's and gets very loud when the turbo spools in. It appears to be under the driver side and I just can't find it. It could possibly be a sucking noise cause when I'm driving and hear it and put my hand under the dash I really can't feel any air movement. Air tanks are running at 120psi and the air drier is cycling. Like I said it only does it at high rpm's when the turbo kicks in. Thoughts ??

 

[dmetalmiki]

Well I for one don't see any connection between the turbo and in cab piping. I'm wondering if pehaps you are hearing a waste gate overblow? That problem must be driving you nuits. At what (exact and repeated) R.P.Ms. does the noise "kick in"? If it was a saracen I would suggest cooling turbine noise.

 

[DocPA]

This is the 8.3 cummins. Starts coming in around 16-1700. Comes in loud between 18-2100. Soon as the trans shifts it goes away till you get back in the turbo power band again. Can't reproduce it with the truck sitting and tromping it to the floor. Only under load driving. Never heard anything like it.

 

[MtnSnow]

Check the air line that goes to the "filter-minder"

 

[Suprman]

Maybe an intake vent line is plumbed wrong and under high rpm the engine is drawing that much air that you hear it.

 

[DocPA]

Where's that filter minder line plumbed to?

 

[MtnSnow]

The minder is plumbed into the engine compartment and is connected to the air filter piping that comes up between the engine & frame from the air filter housing under the drivers door.

 

[wreckerman893]

The windshield wipers are air powered and the plumbing is behind the dash around the steering wheel. Might want to check the lines and the position of the wiper switches.

 

[Scott88M]

Also there are ctis air hoses under the dash too.

 

[Shirehorse]

Is there a line under there for the air gauge like on the older M809 series? Mine was damaged at one of the fittings, and leaked air from around said fitting. Not enough to cause the light and low air buzzer to activate, but enough to be annoying.