Got an M1078A1. New tires, the purge valve (center of vehicle right side above exhaust tubing) always stays open and slowly drains the tires flat. Changed ecu (flashy thing on drivers side with buttons), manifold thing (passenger side kick panel), sensor and regulator thing (just off the wet tank), and the valve itself. It's still draining tires...what's next?
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You might have gotten a little better response if you had posted this in Current Conflict, FMTV. Can't always know where to put things - and for all I know - as a new member this (Conversations) may have been the only place you could post. ANYHOW, link below is where you should find discussion threads about your truck.
Post up your Family of Medium Tactical Vehicles Q&A here.
www.steelsoldiers.com
That purge valve on the air dryer sometimes sticks open. Guessing that you have the "factory original" piece. Many times, you can get the truck running, air up to about 60# or so, then climb down and put the flat (palm) of your hand up to the black plastic blowing air and push up. Sometimes that will seal the purge. Disassembling it and cleaning it will fix what the "hand trick" won't do. Picture below.
Now, as for the CTIS draining and emptying your tires... I think you have two problems.
Purge Drain is
Problem One.
CTIS draining your tires are
Problem Two.
MY OPINION is that you need to solve Problem One before going any further. You need to be able to turn off the truck with full air tanks. The motor makes too much noise to allow you to find any other air leaks. If you have "house air" (an air compressor and a hose) available attaching a glad hand to the left front glad hand. That will allow you to quietly hunt for leaks. First by sound, then with Dawn dish soap diluted with water and a spray bottle.
Several CTIS components are under the dash on the right side of the truck. You hay be able to hear it clicking and clacking - opening and closing air valves. A picture of basic components is below. That number TM-9-2320-363-20-1_199_1 is the Technical Manual that may be really useful.
There are several threads in the LMTV section about troubleshooting the CTIS air system. If you can't find anything using SEARCH, let me know and I will post a few links or some of the things I have downloaded from other members.