CTIS issues

[VikingatWar]

Gentlemen, my 91 M925 CTIS seems to be cycling but not actually filling tires. Upon starting the truck, the system builds up pressure on both gauges but once it reaches operating pressure the system seems to keep recycling. A relief valve or something under the dash seems to bleed off a quick burst of air every 10 seconds or so.

Also, I had a very slow leak on a rear tire at the valve which I repaired. I figured that starting the truck would get the CTIS to fill the now empty tire. The CTIS system had no effect on the flat. I had to fill the tire manually.

The CTIS on my H1 works much differently. It will fill tires from flat and is not "computer" controlled.

Any help on this would be appreciated. I know many just unplug the system but I like everything to work and work correctly.

 

[Gunzy]

Another example of why I am not a CTIS fan. My truck is old school, gladhand tire hose for air.

 

[VikingatWar]

Yes, sometimes simple is better. The CTIS system has many advantages that make it worth having and maintaining. Besides the ability to "air-down" or back up on demand as necessary for traction conditions, the system provides the ability to keep rolling with a big tire leak. Who wants to call a tow truck?

On my Hummer, I had a sidewall leak in a front tire. I isolated the tire on the CTIS system and left the compressor running. The tire maintained about 30 PSI even with air blowing out of the hole in the side wall. I was able to drive home and make repairs. This saved me quite a bit in towing fees.

Additionally, that CTIS system allows me to hook up a hose and fill other peoples tires or fun stuff like tubes and rafts when camping.

 

[Gunzy]

I admit CTIS does have it's place. I can also air up other stuff with out having CTIS. And in case of flat I have AAA RV Plus to call if needed. If they will cover a 40' bus chassis motor home they should cover my M923.

 

[VikingatWar]

Triple AAA covers stuff that big? That's good to know. I wonder if the roadside assistance on AMEX covers large vehicles. Still hate getting towed.

I see you have a Bricklin. My friend has one, green.

 

[Gunzy]

AAA RV should cover it. Basic AAA won't. But it needs to be privately owned and not use commercially. Of course now I'm going to call and check. They will cover a BIG honkin' Motor home, my 5 ton shouldn't be any different.

 

[Mercunimog404]

The American industry just can't seem to get ctis working. Unfortunately. The soviets had it back in the what 70s and it worked as with the Germans on the Unimog.

 

[Iggy913]

CTIS is a great idea, just a somewhat poor execution. The computer in the loop and all the excess filters and fittings are problematic to say the least. On my truck I can start it 10 times in a row and the CTIS works as advertised, then it seems to go on a run of as many starts where it doesn't even come on at all.

American Industry does have CTIS figured out, it's commercially available and used on dump trucks, logging trucks, and concrete mixers without issue. The CTIS on all the military trucks prior to, what an H1, was just a little too fancy for it's own good. I bet if you knew what you were doing you could set up a "manual" CTIS system with a line from each tire to valves located in the cab. I mean look at all the air suspension systems on the market, most are adjustable inside the vehicle with a command module of some kind.

 

[Mercunimog404]

CTIS is a great idea, just a somewhat poor execution. The computer in the loop and all the excess filters and fittings are problematic to say the least. On my truck I can start it 10 times in a row and the CTIS works as advertised, then it seems to go on a run of as many starts where it doesn't even come on at all.

American Industry does have CTIS figured out, it's commercially available and used on dump trucks, logging trucks, and concrete mixers without issue. The CTIS on all the military trucks prior to, what an H1, was just a little too fancy for it's own good. I bet if you knew what you were doing you could set up a "manual" CTIS system with a line from each tire to valves located in the cab. I mean look at all the air suspension systems on the market, most are adjustable inside the vehicle with a command module of some kind.

I'm not sure whats wrong with the military then. But the again the Ctis we have in the lmtvs has been reliable.

 

[Suprman]

M939a2 trucks are 20 plus years old. If you went thru the entire system and made sure there were no leaking lines, put new o-rings all around including the valve body, rebuilt or replaced the wheel valves, made sure the hub seals were all new and sealing tight and then verify the controller was properly working then I'm sure it would work fine probably for some time. But like anything else on these trucks it needs to be maintained and I think it's one of those things that the military units overlooked and then over time it just got a bad rap.

 

[Suprman]

If the wheel valves are all working properly, there shouldn't be much air seepage. You are going to get a little over time but the system is supposed to come on automatically and top off the tires each time it is run. I believe highway pressure is around 65psi. Dump pressure is a constant 20psi this keeps the wheel valves open and will allow tire pressure to escape. The fill side air lines are the main source of the ctis issues. Air comes out of the valve body and goes out to the 3 axles, thru the 3 quick release valves and splits off to each hub. It goes in thru the hub and then out the front thru a line coming out of the hub, then thru the wheel valve and then another line going to the wheel stem. Plenty of places to develop issues unfortunately.

 

[BrainP]

CTIS is a great idea, just a somewhat poor execution. The computer in the loop and all the excess filters and fittings are problematic to say the least. On my truck I can start it 10 times in a row and the CTIS works as advertised, then it seems to go on a run of as many starts where it doesn't even come on at all.

American Industry does have CTIS figured out, it's commercially available and used on dump trucks, logging trucks, and concrete mixers without issue. The CTIS on all the military trucks prior to, what an H1, was just a little too fancy for it's own good. I bet if you knew what you were doing you could set up a "manual" CTIS system with a line from each tire to valves located in the cab. I mean look at all the air suspension systems on the market, most are adjustable inside the vehicle with a command module of some kind.

I'm thinking about trying this. More or less a regulator and guage to start.

 

[HASSON1911]

My CTIS likes to act up, but after getting the spicer manual I've learned that if one light is blinking(the setting you have selected) dont worry its working fine even if it blows a relief valve. Now every now and then it has four blinking lights, I just reset it about 5 or 10 times and it goes again, Why it does this who knows, the manual gives very vague description for quick diagnostic. I'll keep pick till it stops working then disable it when she finally goes, its a very nice thing to have but for private hands I don't think most wallets could handle the repair bill.

 

[Suprman]

You would need a regulator so you could send 20psi thru the system to dump air and then an air supply to fill probably set to around 60psi so you dont accidentally overfill. But if the fill side is working properly then the system more than likely will be working. Most of the fault issues are in the fill side air feed from leaks.

 

[chp925]

how do you reset the ctis mine has all 4 blinking lights

 

[HASSON1911]

when that happens to mine i either reset it till it works or i hit the emergency and let it fill for about 2-3 min. then hit highway button again, from what I understand one or more tires is below the recommended tire pressure that the computer is set at and it will go into safety mode to protect the other tires.

 

[chp925]

what i am getting is all 5 lights blinking i tried today to let the air build pressure the shut the truck off then back on and hit run flat and it lite up for a second then they all start blinking again so i tried it again this time i hit emergence and the emerg. light and hwy stayed on. now every time i hit a button i here the valve in the cab click then i hear the valves outside the truck dump air for a second then it waits a few seconds then dumps again and that is it. then all the lights start blinking again anyone have any idea's i really want to get it working
thanks
rob

 

[chp925]

and what do you do to reset the system???

 

[Suprman]

Look for air leaks around the wheel valves when it does its pressure check. If the tires are low manually air them up. The rear wheel valves come loose sometimes. The system is reset by shutting off and restarting the truck.

 

[ZZ4x4]

Gentlemen, my 91 M925 CTIS seems to be cycling but not actually filling tires. Upon starting the truck, the system builds up pressure on both gauges but once it reaches operating pressure the system seems to keep recycling. A relief valve or something under the dash seems to bleed off a quick burst of air every 10 seconds or so.

Also, I had a very slow leak on a rear tire at the valve which I repaired. I figured that starting the truck would get the CTIS to fill the now empty tire. The CTIS system had no effect on the flat. I had to fill the tire manually.

The CTIS on my H1 works much differently. It will fill tires from flat and is not "computer" controlled.

Any help on this would be appreciated. I know many just unplug the system but I like everything to work and work correctly.

Viking,
Your CTIS is working properly from what you've described. The system waits from pressure to build in the tanks and then starts the fill process. The air valve in the cab sends air to the three quick release valves at each axle until air tank pressure decreases at which time it pauses as the compressor refills the tanks. The filling is much better at higher RPMs after you get underway. At idle the system will turn on and off the fill every ten seconds or so ( as you described). The fact that you can't fill an empty tire is normal. You need above 20 psi in the tire and in some cases more. The system does a check of air pressure at each QD valve. A flat on one tire will cause an error and you will get blinking lights on the CTIS panel. Fill all tires to normal operating pressure manually and then start the truck. You should be able to raise and lower pressure using the buttons.