CTIS Troubleshooting Question

[KN6KXR]

So I'm after my M936A2 CTIS system. Trying to get it operational. It fails and flattens the tires. I have a major leak or error someplace. The control solenoids are good, I've refitted the updated transducer, works as it should. Now I'm updating all the wheel QRV's and lines to the new style. As I'm doing this I'm trying to come up with ideas to isolate parts and I thought of this:
-If one were to install schraeder valves in the lines from the QRV's to the tire then will it still do the check and pass as if it were normal? This assumes the tires are only in inflation check, below the target pressure, and would not be able to deflate. Still work?
-If one were to install a tank valve with schraeder and cap in the end of the hose to the QRV (essentially dead ending it) would it still pass the same inflation start up check?

I'm trying to come up with something easier to detect something like a hub leak. Easier than the process outlined in the TM. Something that can be done from the outside of the rim without finding the right plugs for the lines and adapters and whatnot. Any advice or experience appreciated!

 

[Mullaney]

So I'm after my M936A2 CTIS system. Trying to get it operational. It fails and flattens the tires. I have a major leak or error someplace. The control solenoids are good, I've refitted the updated transducer, works as it should. Now I'm updating all the wheel QRV's and lines to the new style. As I'm doing this I'm trying to come up with ideas to isolate parts and I thought of this:
-If one were to install schraeder valves in the lines from the QRV's to the tire then will it still do the check and pass as if it were normal? This assumes the tires are only in inflation check, below the target pressure, and would not be able to deflate. Still work?
-If one were to install a tank valve with schraeder and cap in the end of the hose to the QRV (essentially dead ending it) would it still pass the same inflation start up check?

I'm trying to come up with something easier to detect something like a hub leak. Easier than the process outlined in the TM. Something that can be done from the outside of the rim without finding the right plugs for the lines and adapters and whatnot. Any advice or experience appreciated!

.
Couple of things to consider:

The truck makes a racket when it runs. All of them do... Bypass that with a gladhand attached to the front drivers side of the truck from "house air" if you have a compressor. Turns off the truck and lets you hear what is going on. Maybe it is a leak that you can solve.

Another idea is schrader valves like you mentioned. You can air up the tires with an air chuck attached to that same gladhand on the front of the truck. Letting air out is pretty simple. Bypass the entire CTIS with the schrader valves in place and buy air down caps. You screw them onto the schraders and it lowers the pressure to a preset poundage. There are static settings and adjustable poundage caps. Lots of "Jeepers" do it that way...

At least until you find the problem - that will work.

 

[KN6KXR]

Thanks yes I've setup a separate regulator off my shop air and string 125psi air over. Added an additional inline moisture separator as well. My compressor is in a location that can barely be heard where I work on my rig. Whatever the leak is it's pretty big. As the truck airs up my 5hp Quincy with a 60 gallon tank cycles A LOT. More than it should. The strange thing? I can't pinpoint the air leak! Pretty sure the right rear front has a bad hub seal but the area around the drum is so large it's just hard to tell. The system will make it (or look like it will) if the tires start close to target and are aired to HWY but if you go to any lower setting it'll flip out and air them all down to basically sand. 20 to 30psi then flip out and the 5 blinking lights of death..... The thing is the only way to air them back up is by hand and after going from 25 to 80 all around time and again this shit is getting really old.

I ordered a couple of hub seal kits from Big Mike's Motor Pool. I'll go after the suspect hub first. I expect I'll be doing more. Also looks like I'll have to do the leak down tests per the TM. Those hubs should take 80 and drop to no less than 70 over 1 hour.

Truck is a minty reman BUT did sit outside for 4 or 5 years and then live in a aircraft hangar for another 6 or 7 years. Story is the CTIS worked when picked up in '16 but failed on the 900 mile trip home then never got fixed. Vehicle had 2090 miles when I got it. You can tell different guys were working at the depot and some were better than others. Left axle bolts were all to torque spec and had wavy lock washers; right side axle bolts all loose with split locks. Funky. I'm guessing between the workmanship and age I'll be after them all and many other things as time goes by.

 

[Mullaney]

Thanks yes I've setup a separate regulator off my shop air and string 125psi air over. Added an additional inline moisture separator as well. My compressor is in a location that can barely be heard where I work on my rig. Whatever the leak is it's pretty big. As the truck airs up my 5hp Quincy with a 60 gallon tank cycles A LOT. More than it should. The strange thing? I can't pinpoint the air leak! Pretty sure the right rear front has a bad hub seal but the area around the drum is so large it's just hard to tell. The system will make it (or look like it will) if the tires start close to target and are aired to HWY but if you go to any lower setting it'll flip out and air them all down to basically sand. 20 to 30psi then flip out and the 5 blinking lights of death..... The thing is the only way to air them back up is by hand and after going from 25 to 80 all around time and again this shit is getting really old.

I ordered a couple of hub seal kits from Big Mike's Motor Pool. I'll go after the suspect hub first. I expect I'll be doing more. Also looks like I'll have to do the leak down tests per the TM. Those hubs should take 80 and drop to no less than 70 over 1 hour.

Truck is a minty reman BUT did sit outside for 4 or 5 years and then live in a aircraft hangar for another 6 or 7 years. Story is the CTIS worked when picked up in '16 but failed on the 900 mile trip home then never got fixed. Vehicle had 2090 miles when I got it. You can tell different guys were working at the depot and some were better than others. Left axle bolts were all to torque spec and had wavy lock washers; right side axle bolts all loose with split locks. Funky. I'm guessing between the workmanship and age I'll be after them all and many other things as time goes by.

.
Sounds familiar. These trucks definitely seem happiest when they are used regularly. Sitting seems to kill things for no good reason... Glad to hear that you have easy access to shop air. That will help for sure and hopefully a few rubber parts will make it happy again.

There were "hacks" in the military just like in the real world I guess. I have been working on two M108x trucks for the past 18 months slowly fixing things like you described. Some proper and others nothing more than a cobbled together mess. Eventually it improves though with enough time and parts.

There are definitely lots of CTIS troubleshooting posts, so if you get stuck there is a wealth of information out there.

 

[Jbulach]

IIRC, CTIS will time out and go to 5 flashing with shrader valves at all 6 wheels. Not sure how many it can handle and still function.

Block off the line to the hub in question. Hit the emergency button when tracking leaks, that will keep the system from timing out as fast and do pressure checks more frequently.

First put shraders in all the wheels and confirm you don’t have any substantial leaks in the tires/wheels (ie, one or more tire goes down in the normal time the truck sits not used). The nature of the wheel valve on this single circuit system is if one tire is at lower pressure, it will dump air out of the other tires until they get down to or the low tire gets up to equal pressure, or possibly cause a time out if you don’t push the emergency button. Also run the engine at WOT if necessary when airing up.