Chasing Air Leaks...?

I've been having some issues with air leaks.

Issue 1: For quite some time, my air dryer has been "leaking" from the purge valve. With the engine off, the purge valve will continue to hiss for about 2-3 minutes with no air loss. I have been told by a Peterbilt technician this is "normal," despite the fact this dryer has never done this before, until it started doing so. I was further advised to replace the air dryer filter, which I did, yielding the same results.

Issue 2: Yesterday, I replaced a bad shark bite from the supply line going into the primary air tank. This fixed that leak, but now I noticed a new "leak" coming from around the foot control pedal, but not the actual foot pedal itself. I can feel air near the frame, but I cannot see any air lines, let alone any air lines or fittings that may have been compromised. Even more puzzling, the hissing will stop after the PSI reaches 110 for both tanks, with the engine off.

I performed an air brake test and everything passed. However, after sitting parked overnight, I lost half of my air pressure in both tanks. If I let it sit all weekend long, all pressure is lost.

Has anybody else ever had this issue before? Any ideas what it could be? Any help on this is greatly appreciated.

 

Thanks for the help, guys. I replaced the dryer purge valve, which helped (air "purge" time dropped to about 30 seconds after the cutoff.) Unfortunately, the "leak" or "purge" is still happening after the governor activates.

Oddly enough though, if I manually purge air by pumping the brakes a few times, it stops. Also, if I turn off the engine before the governor kicks in, no "purge" or "leak."

This truck is nothing special at all, just a 2014 337 single-axle flatbed. I'll definitely look into getting the plumbing schematics for this thing though. I believe I've narrowed it down to the discharge line from the compressor to the dryer, but I can't see what exactly I'm touching. Just praying DOT doesn't put me OOS for what would otherwise be a "normally functioning" air system.