Loosing air pressure when engine is running.

I have freightliner cascadia 2015 truck is parking .engine is running. slow air built 5 minutes to purge. Start loosing air and purge cycling every 1 minute. When shutting of the engine its hold the pressure. no stattic air leak .for fan cluch I have swith to cut off the air . No change.replaced new air compressor new discharge hoses new tank new air dryer and governor. On gagues the secondary gague start loosing air. Truck is parking and running no brake no transmission engaged.

 

I have ultra sound device for air leak checking .used while engine is off no air leak .

 

Tomorrow I'll disconnect every hose connected to secondary tank an block it from tank . One by one .and see if I have leak or not.

 

New discharge line replaced from air compressor to air dryer.