CTIS trouble shooting

[Celticlady]

1999 LMTV
All lights flash on the CTIS. I followed the manual to reset. Doesn't help. Guy on YouTube replaced the pressure switch on side of wet tank. Seemed to fix his. But didn't mention the PN or where he got it. I found the manual reference to change that switch. Can't seem to find a PN.

 

[Ronmar]

The pressure switch provides a path to ground when the tank goes above 117 PSI, and removes that ground connection when the tank drops to 89 PSI. I think I would first make sure it is bad before I replaced it...

1. Do you hear any noise coming from under the passenger dash, click of solenoid valves, movement of air? Tank has to go over 117 and that switch close before CTIS does anything. If it is trying to work, the switch is probably OK. If this is the case, you most likely have an air leak. With the truck full of air, shutoff the engine. Disconnect the cannon plug at the CTIS controller and install a jumper from H to R. This will power the control solenoid(It has to be powered for the PCU to do anything. turn on the main switch and with a second jumper briefly jumper H to B for about 1 second then remove it, this will open the supply solenoid you will hear ir flow and all the system valves will open and the tire pressures should equalize. The system will stay pressurized as long as the H-R jumper is powering the control solenoid. Now find the leaks. When you are done pull the H-R jumper or turn off the main switch to open the control solenoid and vent the system/close the valves...

2. If it is not operating at all(nothing happens), Is your wet tank going above 120 PSI. The governor should be set for 125 PSI. and if the tank is not getting that high, the switch is doing it’s job And you have an air supply problem.

3. you can measure the switch contacts with an ohmmeter. Start the truck and let it fill till the governor kicks off/air dryer purges. The switch contacts should be closed/shorted. Shutoff the truck and with the ohmmeter looking at those contacts, open the wet tank drain and look for the contacts to open at some point.

4. if the switch tests bad, you can jumper the connections in the plug and simulate to CTIS a full tank To see if the rest of the system is operational...

 

[Celticlady]

Wow! Thank you. I have my homework assignment

I followed the manual. If all lights are flashing. Shut everything off. Shut off engine.
Turn on the main power swt. Push the run flat. Start engine.

The run flat AND the hwy lights flash. After the engine is running for maybe 2-3 min. All lights start flashing AND there is a solenoid that opens, air vents and closes. This repeats all the time. It sounds like it under the dash on center or the rh side.

there is guy that has a YouTube video of the same thing.

 

[Ronmar]

Wow! Thank you. I have my homework assignment

I followed the manual. If all lights are flashing. Shut everything off. Shut off engine.
Turn on the main power swt. Push the run flat. Start engine.

The run flat AND the hwy lights flash. After the engine is running for maybe 2-3 min. All lights start flashing AND there is a solenoid that opens, air vents and closes. This repeats all the time. It sounds like it under the dash on center or the rh side.

there is guy that has a YouTube video of the same thing.

Sounds like you have a leak. It does something and does not see the expected result(stable pressure during a pressure check, inflate or deflate after that commanded action). I suspect you have a big leak, which will become really obvious after you pressurize the system with the engine off. Mine sure did

you can also charge the air system by connecting shop air to the front red/emergency glad-hand. Just chok the wheels as this also releases the parking brakes...

 

[Celticlady]

First thanks.

That little tip about putting shop air in gladhand was a gem.

yes I have a big leak. I was messaging with someone else about this.
My air brake release valve leaks around the stem below the handle.
The OEM valve leaked some. Especially if you pushed the handle off the side. I bought a new valve from Midwest Military Equipment. It is not a OEM but all the ports were in the right spot. I installed it.
IT LEAKS 10 WORST THAN ONE I REMOVED. You can hear it hissing all the time. If you push the handle off to one side it will blow your hat off.

I have been told that all though “new” it probably sat on a shelf and the o-rings are shrunk/deteriorated.
Its not known if I could disassemble and replace the o-rings.

It was a awful job to replace that valve. Would like to know I have a good valve before I do it again.

I drive the Volunteer Fire trucks. None of their air brake valves leak. So I have been trying to figure out WTH happen.

 

[Third From Texas]

My air brake release valve leaks around the stem below the handle.

Not an uncommon thing for a truck that's been sitting. A shot of WD40 around the stem with the system discharged can often lube the chamber enough to square it away for good (saved me from replacing mine and all three trucks had a slight leak there).

I bought a new valve from Midwest Military Equipment. It is not a OEM but all the ports were in the right spot. I installed it.
IT LEAKS 10 WORST THAN ONE I REMOVED. You can hear it hissing all the time. If you push the handle off to one side it will blow your hat off.

Well, lesson learned. At least they only marked it up 2000% over what the exact same item costs from a civilian supplier.

1) Just because it's "surplus green" does not make it better or even good
2) Any company with "surplus", "military", especially god forbid any point of the compass in their name should be eyed with MUCH scrutiny.

I have been told that all though “new” it probably sat on a shelf and the o-rings are shrunk/deteriorated.

You've been told the truth. There is a reason the government threw this stuff away in the first place. Be *especially* suspect of anything rubber (cab bushings, hose, valves, tires, etc).

It was a awful job to replace that valve. Would like to know I have a good valve before I do it again.

That's a VERY common semi truck part. They can be found as individual valves or dual. Either will work (unless it's an A1R truck which used the dual valve), but the dual valves will require some additional fittings for clearance. Never looked into the rebuild possibilities (it's a $20 part).

 

[Celticlady]

Not an uncommon thing for a truck that's been sitting. A shot of WD40 around the stem with the system discharged can often lube the chamber enough to square it away for good (saved me from replacing mine and all three trucks had a slight leak there).

You are the second to suggest that. Just haven't gotten to it. Will try it today. But this valve leaks so bad not sure it will help.



Well, lesson learned. At least they only marked it up 2000% over what the exact same item costs from a civilian supplier.

1) Just because it's "surplus green" does not make it better or even good
2) Any company with "surplus", "military", especially god forbid any point of the compass in their name should be eyed with MUCH scrutiny.



Well its not green, in fact Its not even OEM part for this truck. Has a blue knob that is NOT interchangeable with old knob. Looks new.
I bought it from the same people I bought the truck from.
It wasn't $20 ($60) so not quite 2000% Oh and that included shipping. So if you have shipped anything in the last 6 mths that could account for the difference.


Regardless. The CTIS problem has not changed, for better or worst.

 

[Ronmar]

First thanks.

That little tip about putting shop air in gladhand was a gem.

yes I have a big leak. I was messaging with someone else about this.

Did you find a leak in CTIS? The park or trailer brake valve leak would not effect CTIS...

 

[Celticlady]

Did you find a leak in CTIS? The park or trailer brake valve leak would not effect CTIS...

Glad for the clarification.

 

[Celticlady]

The pressure switch provides a path to ground when the tank goes above 117 PSI, and removes that ground connection when the tank drops to 89 PSI. I think I would first make sure it is bad before I replaced it...

1. Do you hear any noise coming from under the passenger dash, click of solenoid valves, movement of air? Tank has to go over 117 and that switch close before CTIS does anything. If it is trying to work, the switch is probably OK. If this is the case, you most likely have an air leak. With the truck full of air, shutoff the engine. Disconnect the cannon plug at the CTIS controller and install a jumper from H to R. This will power the control solenoid(It has to be powered for the PCU to do anything. turn on the main switch and with a second jumper briefly jumper H to B for about 1 second then remove it, this will open the supply solenoid you will hear ir flow and all the system valves will open and the tire pressures should equalize. The system will stay pressurized as long as the H-R jumper is powering the control solenoid. Now find the leaks. When you are done pull the H-R jumper or turn off the main switch to open the control solenoid and vent the system/close the valves...

2. If it is not operating at all(nothing happens), Is your wet tank going above 120 PSI. The governor should be set for 125 PSI. and if the tank is not getting that high, the switch is doing it’s job And you have an air supply problem.

3. you can measure the switch contacts with an ohmmeter. Start the truck and let it fill till the governor kicks off/air dryer purges. The switch contacts should be closed/shorted. Shutoff the truck and with the ohmmeter looking at those contacts, open the wet tank drain and look for the contacts to open at some point.

4. if the switch tests bad, you can jumper the connections in the plug and simulate to CTIS a full tank To see if the rest of the system is operational...

3) pressure relief pops at 120. Pressure swt closed. Open at 89.

Had to dig around to find some CP pins.

Jumper H to R
turn on pwr swt.
Momentarily jumper H to B.
loud air venting as long as I hold B. If I hold it -all the air goes out and cab settles in about 10 seconds.

2) compressor pumps frt & r brakes gauges to 90 in about 3 min. Cab raises at 70ish. R brakes gauge indicates 120 at pop off. Ft is about 100ish. Ft gauge is jumpy.

If I am understanding correctly Sounds like I have a hose or seal failure. RH side somewhere. I am going to have to get help. It bleeds off to fast to find by myself.

oil in brake valve is helping a lot in just 2 hr soak.

 

[Ronmar]

3) pressure relief pops at 120. Pressure swt closed. Open at 89.

Had to dig around to find some CP pins.

Jumper H to R
turn on pwr swt.
Momentarily jumper H to B.
loud air venting as long as I hold B. If I hold it -all the air goes out and cab settles in about 10 seconds.

2) compressor pumps frt & r brakes gauges to 90 in about 3 min. Cab raises at 70ish. R brakes gauge indicates 120 at pop off. Ft is about 100ish. Ft gauge is jumpy.

If I am understanding correctly Sounds like I have a hose or seal failure. RH side somewhere. I am going to have to get help. It bleeds off to fast to find by myself.

oil in brake valve is helping a lot in just 2 hr soak.

Yep, loud air venting when you jump H to B(supply) well thats your CTIS problem(one of them anyway). Isn’t it amazing what you can hear when the cat isn’t “Purring” The tires take a lot of air. When inflating on mine at low tire pressure it will drain a full wet tank down to 85 in 3 seconds. Then the engine driven compressor at idle takes about 10-12 seconds to refill it

The regulator looking thing on the wet tank is an air brake protection valve. it only allows flow out when the wet tank goes above 85 PSI. It feeds CTIS and the cab air suspension, so either it is out of wack or your gauge is, as the cab shouldn’t start to raise untill the wet tank and the front/rear gauges go over 85 PSI... it is designed this way so the brakes always get at least 85PSI...

yep, a little oil on the park valve plunger stem can do wonders but you are probably only delaying the inevitable a little...

here is a fairly easy way to check and confirm tank pressure against the installed gauges. Cobbled together with parts in the air drawer of my toolbox. Just jam the rubber tip of the blowgun in against the tank drain while holding the lever on, then open the drain valve...

 

[Celticlady]

Yep, loud air venting when you jump H to B(supply) well thats your CTIS problem(one of them anyway). Isn’t it amazing what you can hear when the cat isn’t “Purring” The tires take a lot of air. When inflating on mine at low tire pressure it will drain a full wet tank down to 85 in 3 seconds. Then the engine driven compressor at idle takes about 10-12 seconds to refill it

The regulator looking thing on the wet tank is an air brake protection valve. it only allows flow out when the wet tank goes above 85 PSI. It feeds CTIS and the cab air suspension, so either it is out of wack or your gauge is, as the cab shouldn’t start to raise untill the wet tank and the front/rear gauges go over 85 PSI... it is designed this way so the brakes always get at least 85PSI...

yep, a little oil on the park valve plunger stem can do wonders but you are probably only delaying the inevitable a little...

here is a fairly easy way to check and confirm tank pressure against the installed gauges. Cobbled together with parts in the air drawer of my toolbox. Just jam the rubber tip of the blowgun in against the tank drain while holding the lever on, then open the drain valve...

View attachment 830583

The lines on the gauges are approx. I’ll pay closer attention to them. I have lots of brass fittings and an assortment of gauges. I will “T” a gauge between the drain valve and tank. I was thinking about putting in a quick disconnect for shop air there.
I have a friend coming over Friday to listen when I trigger B.

I found a container full of cannon plug pin/recepticals. I used to work avionics. So I won’t have to cobble jumpers now

you have been a great help.

Hopefully I won’t need to know about those “other problems “

 

[Celticlady]

Update.

My friend came over to help locate the CTIS leak. While I was waiting the couple of days for his schedule to clear, I plumbed in a gauge and a shop QD. Now I don't need to run the engine to fill the air tanks. The shop air will maintain it while trouble shooting.

Found three leaks. One was a duh monument. I had a rear tire off and the CTIS hose didn't get tighten down. Easy

I had the the dump bed mod done on my truck. Apparently the dipweeds burned 2 holes in the plastic CTIS tubing near the cross beam that the life actuator is mounted on while welding.

There is a regulator or valve (There are NO wires) on the back side of the cross beam above the rear axle. The tube that has the holes in it goes to this item. It was venting a LOT of air. When My buddy put his finger over the burn holes in the tubbing this item mostly quite venting. So I hope when the tubbing is repaired this will cease to be a problem.

Lucky the plastic tubbing is 1/2 so I can go to a hardware store and get some compression sleeve connectors.

RonMar The CTIS plug jumper is a great trouble shooting tool. My 3 way jumper made with cannon plug pins was perfect. Thanks Reminds me of working on 767s

My buddy has FMTV. So he was paying a lot of attention.

I'll update tomorrow.

 

[Ronmar]

Update.

My friend came over to help locate the CTIS leak. While I was waiting the couple of days for his schedule to clear, I plumbed in a gauge and a shop QD. Now I don't need to run the engine to fill the air tanks. The shop air will maintain it while trouble shooting.

Found three leaks. One was a duh monument. I had a rear tire off and the CTIS hose didn't get tighten down. Easy

I had the the dump bed mod done on my truck. Apparently the dipweeds burned 2 holes in the plastic CTIS tubing near the cross beam that the life actuator is mounted on while welding.

There is a regulator or valve (There are NO wires) on the back side of the cross beam above the rear axle. The tube that has the holes in it goes to this item. It was venting a LOT of air. When My buddy put his finger over the burn holes in the tubbing this item mostly quite venting. So I hope when the tubbing is repaired this will cease to be a problem.

Lucky the plastic tubbing is 1/2 so I can go to a hardware store and get some compression sleeve connectors.

RonMar The CTIS plug jumper is a great trouble shooting tool. My 3 way jumper made with cannon plug pins was perfect. Thanks Reminds me of working on 767s

My buddy has FMTV. So he was paying a lot of attention.

I'll update tomorrow.

That is your rear axle CTIS dump valve. It is basically a remote pressure regulator. If the tube feeding it was leaking, and the tire pressure was greater than the line pressure, that valve would dump to try and get it’s output to equal the leaking input line pressure. Basically giving it a deflate command

Bed looks nice...

 

[Celticlady]

That is your rear axle CTIS dump valve. It is basically a remote pressure regulator. If the tube feeding it was leaking, and the tire pressure was greater than the line pressure, that valve would dump to try and get it’s output to equal the leaking input line pressure. Basically giving it a deflate command

Bed looks nice...

Great! So its a differential pressure valve. When I fix the leak it will operate as required.

Thanks. I hauled 25 loads of gravel out my neighbor's creak for his driveway about 3 weeks ago. He wants to buy my truck.... ha ha ha But now I can use his excavator yeah

 

[Celticlady]

Great! So its a differential pressure valve. When I fix the leak it will operate as required.

Thanks. I hauled 25 loads of gravel out my neighbor's creak for his driveway about 3 weeks ago. He wants to buy my truck.... ha ha ha But now I can use his excavator yeah

Update
Replaced about 6 in of black plastic CTIS line that had 2 holes in it from previous welding nearby. I was fortunate it didn’t get into the wiring at same spot.

Using the jumper I could hear air being routed to the tires at each tire. No apparent leaks. Hooked up the CP to the CTIS controller. Turned on the power. Couple of solenoids cycled, the HWY light ONLY illuminated on the CTIS controller. It stayed that way. Started the the engine, hwy light only came on. Checked all the tire pressure. They all agreed, 55psi.

“Replaced damaged tubing. Leak and ops check normal. Return to service.” ...Sir.


I had to use the white translucent hardware grade of tubing. PBA for now. Where do I get the high pressure DOT grade of tubing?

 

[Ronmar]

Update
Replaced about 6 in of black plastic CTIS line that had 2 holes in it from previous welding nearby. I was fortunate it didn’t get into the wiring at same spot.

Using the jumper I could hear air being routed to the tires at each tire. No apparent leaks. Hooked up the CP to the CTIS controller. Turned on the power. Couple of solenoids cycled, the HWY light ONLY illuminated on the CTIS controller. It stayed that way. Started the the engine, hwy light only came on. Checked all the tire pressure. They all agreed, 55psi.

“Replaced damaged tubing. Leak and ops check normal. Return to service.” ...Sir.


I had to use the white translucent hardware grade of tubing. PBA for now. Where do I get the high pressure DOT grade of tubing?

You can order it from a truck supply, but places like NAPA usually have it on hand, or hit up someplace that services large trucks...

 

[Third From Texas]

Good time to get those tires up to working highway pressure and save tread/improve mileage(?)

 

[Ronmar]

Good time to get those tires up to working highway pressure and save tread/improve mileage(?)

Yep, simple change that will get you right around 82PSI in highway mode. much better pressure for these tires to run at on the highway...

 

[ckouba]

Video has link to sources but doesn't specify which pressure rating. Is there a 75 psi one or which specific transducer do we need? Got an actual part number/supplier?