Air Pressure Drops When Ignition OFF

I had a blow off gun hooked to the seat line that would drain quite a bit of air.

 

Could be leaking in the hand valves on the dash. Not common, but it does happen. I've also had tiny pinholes/cracks in hoses that were not easy to see. As someone else mentioned, spray soapy water on all lines and junctions with components...

Also... Have you considered this could be an air suspension issue? Leveling valves have been known to cause such things, as have ABS valves.

Also, is it an auto-shift? Most of these are air-controlled and I have seen an I-Sh-t equipped Vulva empty its air supply into the trans case unheard with the engine off. Tried to tell the shop supervisor once I thought of it but they wouldn't listen. Took *THEM* MONTHS to "find" it.

 

Yes, DOT will cite you for an air leak whether the truck is running or not, and what your mechanic is telling you about all prostars doing it isn't going to save you from a ticket when DOT finds the leak. Next time you unload set your trailer brakes (if you aren't doing that already) and see if you still lose air. If you don't, the leak is in the trailer. Does it leak as quickly when it is just parked in the fuel aisle? If not, and you have air suspension on the trailer, is the leveler dumping excessively while unloading? Worst case scenario, you are going to have to get under the thing and spray all the air lines and connections and look for bubbles. Sounds like what your mechanic should be doing instead of making excuses.

 

If the leak is not AUDIBLE, the DOT cannot cite you so long as your air-loss rate is within the parameters set forth by the regulations.

Easiest way to search for a leak is to put a quick-connect fitting on your air tank and hook up to shop air, so that your system can remain at full pressure with the truck shut off even with it leaking. Then, go nuts with the soapy water. If you're losing air, it'll make bubbles somewhere.

 

Don't rule out a leak in the air seat diaphragms either. Most people wouldn't think of this one. And isn't the differential lock/switch air-controlled as well? Also, to extend on my thoughts on the air-supension/control. You DO have airbags cushioning the tractor cab from the frame. Could be one of those is bad.

 

Do your airbags Drop when turning off the ignition that’s what my truck does

 

Welcome to the forum, if you look above posts you can see how long the thread has been dead. For instance this 1 died Oct. 30, 2017.

 

To answer your question, if your air system is not tight and leak free, the bags will in time deflate.

 

I don’t know about the ignition thing, but they will the older they get!