peterbilt trailer valve issues

16 pete 389. The tractor valve pushes in fine, the trailer valve will not stay locked down. If I hold it air flows out the line. I took the line off behind dash and it pushes air out if I hold it down. I replaced the inside valve with the same results. The one I replaced it with was a used unit. Any ideas.

 

No air leaks anywhere.

 

Yes you're right. I have hooked an air line to a trailer, an airline to air up tires and left it open and the trailer valve still doesn't stay engaged. It flows air out of it for like 10 seconds if i hold it in. I thought the same thing on tpv but I replaced it today and still the same thing.

 

No it will not. It won't stay in.

 

Yes I checked that today.

 

I mean there's what the dash valve, tpv and the foot valve. No leaks nothing. Truck was fine when parked and it sat for like 3 months and here I am. I don't have to funds really to take it to pete. I'm going to trough a foot valve in it tomorrow morning and probably return the tpv.