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Manual CTIS, electric over pneumatic.

Ronmar

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Ok, so my CTIS ECU is a brick with 5 solid lights and if I spend too much more on this project my wife will probably bury me in it:) That being said, I am also a bit of a control freak so I am converting to manual CTIS.

I have looked at the valve and regulator method but decided to go about it a little differently. I am going to keep and use the solenoid operated PCU for a few reasons:
1. PCU seems reasonably robust and repairable.
2. Can check tire pressure on demand.
3. Such a large truck, so little dash space. The manual control fits where the ECU was.
4. Only permanant mod is a single 3/8” hole behind the ECU.
5. When not in use the PCU depressurizes the system automatically.
6. It is fairly easy for me and cost about $35.

How I did it:
well I scooped out the guts of my dead ECU, carefull not to damage the cannon plug. Then I installed a 0-100PSI Automotive oil pressure gauge in the face, and 3 momentary pushbuttons on the top. I removed the passenger kickplate and unmounted the PCU so I could remove the bottom cover. This allowed me to get a wrench on and remove the pressure transducer. I capped it and re-attached it to the harness and zip-tied it to the harness in case I ever want to go back to an automated system. I installed the hose adapter compression fitting from the oil pressure gauge into the pressure port(it is 1/8” NPT) and re-installed the bottom cover and PCU. Using a fiberglass fish-tape, I fished the 1/8” poly oil pressure line thru behind the heater to below the park brake housing. Carefully marking where the pressure gauge port is on the ECU, I drilled a 3/8” hole behind where the ECU mounts for the line to reach the port on the back of the gauge I placed in the ECU. Mind the air lines inside the park brake compartment, none were in the area I chose to place the gauge, and I had plenty of clearance, but be carefull as you dont want to damage any of those.

On the cannon plug in the ECU, 24V is applied on pin H. Pin R, B and C leave the ECU to the solenoids on the PCU. Pin R is the Control solenoid, Pin B is the Supply solenoid and pin C is the Deflate solenoid.
I connected pin H to the input of the control pushbutton. The output of the control pushbutton goes to pin R and also feeds the input of the supply and deflate pushbuttons. The output of the supply and deflate pushbuttons go to pins B and C respectively. Thats it, I will eventually add the gauge light to the output of the control pushbutton, but have not done that yet.

In order to operate correctly the PCU needs two solenoids activated together. I believe this was done to prevent a single short circuit or stuck valve from overinflating the tires. The resulting explosion from an over-inflated 47” split rim would be nothing short of catostrophic. If you go the manual route, this is one of those details you do not get a second chance to get right, so pay attention to how you manually inflate tires. That is why I used momentary pushbuttons. This requires fingers on 2 buttons to operate, and you cannot just turn it on and forget it...

How it operates:

As I mentioned, it needs two solenoids. In testing I discovered the Control solenoid by itself will slowly apply pressure, the Quick Release valves will squeel/ partially open at some point and eventually close as the pressure builds and eventually you will be left with tire pressure on the gauge once the wheel valves open. This takes 30+ seconds. Releasing control vents the system and all the valves close. Supply by itself jumps to tire pressure then decreases to a point where the QR valves start to squeel and dump. Deflate by itself does absolutely nothing but click the solenoid. Since it requires control, I wired the power to the supply and deflate buttons from the control button.

To Check pressure, depress and hold Control and momentarilly press Supply to apply air to the system and open the wheel valves. When you release Supply the gauge will stabelize on the current tire pressure as soon as the tires equalize.

To Inflate, depress and hold control then check initial pressure as described above. To inflate again press and hold the supply button along with control to feed high pressure air. The gauge will jump up around 80 PSI then drop rapidly to read 5+ PSI higher than the tires while filling. You can recheck actual pressure at any time by releasing the Supply button only. And of course this goes a little faster with increased engine RPM. You can press the Supply button as needed to top off the tires to the desired pressure.

To Deflate, Press and hold Control and then Supply briefly to check initial pressure. Then while continuing to hold Control, press and hold Deflate. This will cause the gauge to drop from current tire pressure to around 6-8 PSI. This drop causes the QR valves to open fully and start venting tire pressure to the atmosphere(woosh sound, not a squeal). To check pressure, release Deflate and momentarilly press Supply to close the QR valves and display current tire pressure...

In the first pic, I am holding the now capped presure transducer and harness in my hand and the compression fitting is installed in the port where the transducer used to live.

The second pic is the modified ECU housing with gauge on the face and new top plate and 3 buttons installed
433ABB5F-BCB8-46B6-9F7F-FC2C07194C35.jpg46F9B46D-17C7-467B-9294-794B98025CBB.jpg

 
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m-35tom

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it would also be very easy to build an electronic micro computer version to replace a failed CTIS control box. but I agree a manual system is better. it it possible to over inflate with this?
 

coachgeo

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... it it possible to over inflate with this?
from his write up

Ronmar said:
...In order to operate correctly the PCU needs two solenoids activated together. I believe this was done to prevent a single short circuit or stuck valve from overinflating the tires. The resulting explosion from an over-inflated 47” split rim would be nothing short of catostrophic. If you go the manual route, this is one of those details you do not get a second chance to get right, so pay attention to how you manually inflate tires. That is why I used momentary pushbuttons. This requires fingers on 2 buttons to operate, and you cannot just turn it on and forget it......
I suspect somewhere in the line that feeds the whole thing one could put a max psi valve that would pop open if total pressure reached 90lb?
 

m-35tom

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I would think it should have redundant safety's since the result could easily be life threatening. I can think of other fairly simple ways to automate the system but this is probably the easiest for most people. Yes a pop off valve and also a close on high pressure switch with a buzzer may be prudent.
 

Ronmar

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It is possible to overinflate with ANY manual system. Might even be possible with an automated system unless the software limited the fill time of a system chasing a false pressure transducer reading... not sure what if any the original CTIS used for safety beyond requiring 2 solenoid circuits to operate... Even an air hose if connected and left unattended/forgotten. It is less likley if it requires direct human intervention. I think I would have to hold those buttons a very long time to overinflate 4 tires. My arm getting tired will do a pretty good job of reminding me to check I think:)

I think it would be fairly easy to add a “T” and a pressure relief valve down in the wheel system feed. Right where the line T’s to go to the fore and aft Quick Release valves perhaps...
 
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Ronmar

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Holy freaken nice job..very clean/safe. I vote sticky if i may.

Some pics of the inners would be nice
Thanks. I will take some pics inside when I make a little more ergonomic case. This was an inexpensive proof of concept and the gauge is a little hard to read setting in the drivers seat. Not much inside, 3 switches, 6 wires a cannon plug and gauge.

Been thinking about it a bit and I might also make one change and add a pressure switch to the gauge line that will open the supply circuit if a max pressure is reached while inflating... Fairly inexpensive mod...
 

coachgeo

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Thanks. I will take some pics inside when I make a little more ergonomic case. This was an inexpensive proof of concept and the gauge is a little hard to read setting in the drivers seat. Not much inside, 3 switches, 6 wires a cannon plug and gauge.

Been thinking about it a bit and I might also make one change and add a pressure switch to the gauge line that will open the supply circuit if a max pressure is reached while inflating... Fairly inexpensive mod...
Updates if any?

question on control button...... 1. could the control button be swapped to a toggle switch on/off? 2. what if you forgot to turn control button off? hopefully most in here would understand what would happen if you forgot to take fingers off of the inflate and deflate buttons.

hmmm.... do they make a two way momentary toggle switch? push one way to inflate..... auto return to center is off, push other way to deflate.
 

Ronmar

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No real update, I unfortunately have a lot of projects and I am building a house. Am typing this while taking a break from struggling to put a windshield in the beast right now:)

Yes you can use a toggle, if you leave control on, the system stays pressurized after checking the pressure/inflating and could leak down and activate the dump valves while driving. Besides leaving a solenoid energized, best to turn it off and purge the system when not actively using it.

They make all kinds of toggle switches...
 

coachgeo

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No real update, I unfortunately have a lot of projects and I am building a house. Am typing this while taking a break from struggling to put a windshield in the beast right now:).....
Sorry to hear your fighting the winshield battle too. Am also dealing with a windshield... trying to get her windshield re-installed. It popped part way out.

Note to self (and others) .. don't leave your cab in tilt over mode overnight.... you risk your windshield working its way part way out.
 
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Keith Knight

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Great solution! Even though my system is working after replacing the ECU 2 years ago. As I start my camper build knowing I need heigher tire pressure to support the added weight I will be converting my old ECU to this method.
Thanks for figuring it out.
 

Grond

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Utah
Great solution! Even though my system is working after replacing the ECU 2 years ago. As I start my camper build knowing I need heigher tire pressure to support the added weight I will be converting my old ECU to this method.
Thanks for figuring it out.
Hello sorry to dig up dust I have built and installed the unit but for some reason I can't push past 45 psi in tires other then that it inflates and deflates fine thoughts?
 

Ronmar

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Hello sorry to dig up dust I have built and installed the unit but for some reason I can't push past 45 psi in tires other then that it inflates and deflates fine thoughts?
First off, Are you sure it is not filling? the tires consume a huge ammount of air. Once you energize the control solenoid(closes its valve) and energize the supply solenoid(opens that valve) to let in air, the wet tank on mine drains to the protection valve cutoff point(85 PSI) in about 3 seconds... It then takes 9-12 seconds For the wet tank to recover back to 120 PSI. It takes a long time to fill the tires from 20 to 60 PSI...

how is your air system working? Charges to 120 PSI in the pri and sec tanks in a reasonable amount of time? CTIS pulls air thru the wet tank protection valve So if that has an issue delivering airflow, you might have trouble feeding the tires, If you disconnect the airline coming out of the protection valve Y0u should be able to get an idea how well it is flowing air...

do you have any leaks in the system? Leaks get worse as pressure increases so a bad enough leak might hit a point where it cannot feed the tires above a certain pressure. When you close the control solenoid, the system should be airtight. When you give a shot of supply air, that pressure should open the wheel valves and the entire system should set at tire pressure as long as the control solenoid remains energized. If you pressurize the system with the engine turned off, you should be able to go over all the plumbing and find any leaks...
 

Grond

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First off, Are you sure it is not filling? the tires consume a huge ammount of air. Once you energize the control solenoid(closes its valve) and energize the supply solenoid(opens that valve) to let in air, the wet tank on mine drains to the protection valve cutoff point(85 PSI) in about 3 seconds... It then takes 9-12 seconds For the wet tank to recover back to 120 PSI. It takes a long time to fill the tires from 20 to 60 PSI...

how is your air system working? Charges to 120 PSI in the pri and sec tanks in a reasonable amount of time? CTIS pulls air thru the wet tank protection valve So if that has an issue delivering airflow, you might have trouble feeding the tires, If you disconnect the airline coming out of the protection valve Y0u should be able to get an idea how well it is flowing air...

do you have any leaks in the system? Leaks get worse as pressure increases so a bad enough leak might hit a point where it cannot feed the tires above a certain pressure. When you close the control solenoid, the system should be airtight. When you give a shot of supply air, that pressure should open the wheel valves and the entire system should set at tire pressure as long as the control solenoid remains energized. If you pressurize the system with the engine turned off, you should be able to go over all the plumbing and find any leaks...
I believe I have a mixture of blockage and leaks been tightening everything down made a direct manual valve today to feed air from the truck constantly as I do not have access to shop air currently. found a couple loose fittings but haven't found any other significant leaks yet. will test and look for more tomorrow
 

MrMikey4026

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An automotive leakdown tester is a godsend for troubleshooting CTIS. Just remove the air line on the left side of the PCU, attach the Leakdown tester and pressure to 50 psi. Go over the air system with soapy water and a spray bottle, paying particular attention to the vents on the quick release valves.
You won't believe how many leaks you will find. The original CTIS computer will detect any leaks and fault out with all lights flashing.
Probably a good plan even if you are converting to a manual system.
 
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