2002 Peterbilt 379 where is my air leak?

I did have the signal line off with air in the tanks, but without the truck running. I'll pull the line again in the morning and see if its leaking while idling.

 

C15. No check valve between the wet tank and the gov or air dryer and wet tank. Trust me I looked, lol.

 

Oh trust me I get that new isnt always good, but hopefully this isn't the case with that part.

Im guessing if I pressurize the supply side from the air compressor with an external air source I can probably get it to replicate the issue without the engine running.

 

Ok, some quick googling shows me the unloader valves in my compressor (Tu-flo 550) seem to be a pretty easy repair. There is a cover on top and the rebuild kit is like $30. Im good with trying that and from what Im seeing, all my signs point to the unloader.

But to be sure, is there a check valve in the air dryer under the filter?

 

I havent pulled my filter yet because I dont have a large enough filter wrench for it, my fuel filter wrench is just barely too small.

Tomorrow Ill pull it and check for any kind if check valve, plus pull my air inlet on my compressor to see how the unloader valve is operating.

There are no other leaks that I can find and my air system has leaked down less than 5psi in almost 4hrs since the last time I checked it. It usually leaks 10psi in 10hrs and will hold a steady 100psi till I start the truck. I have a feeling replacing that check valve on the passenger side will cut that in atleast half.

 

Ah, I misread your post. I'll check it out too.