CTIS issues

[Bill Pfeiffer]

Hi folks, I'm hoping that someone can point me in the right direction. I have an LMTV and went out this morning to find all 4 tires flat. I started it up and got 5 flashing lights on the controller. Tried the reset, but the runflat light will not light, it works otherwise. After a while it will start working correctly and fill the tires, then when I shut it off it makes noise from around the transmission area and there is air coming from the poppet valve on the manifold under the right kick panel. I can't feel the source of the leak underneath, and I donated my hearing to USMC field artillery back in the 70s, so I can't pinpoint it. I'm going to get someone to come over to be my ears, but if anyone could narrow down what I am looking for it would be greatly appreciated...

 

[Keith Knight]

When my CTIS was working then stopped working giving me 5 blinking lights. The end solution was rebuilding the control valve body. It’s located behind the kick panel on the passenger side. Pretty simple to do. 18 months later and still working.

 

[GeneralDisorder]

The only way that can happen (all four tires dump to wheel valve minimum), is for there to be air pressure in the control line from the PCU to the QRV's. Which means the spool valves in the PCU are sticking and letting wet tank air get into the control line keeping it at some pressure above the wheel valve close point - which is typically about 5 psi. That will cause the tires to vent.

Another thing that causes this is a plugged vent between the PCU and the cab bulkhead fitting. Mud wasps are often to blame. On later trucks this was deleted in favor of a simple vent on the side of the unit instead of being plumbed to the cab floor.

Rebuild the PCU after verifying that the vent isn't plugged.

 

[Bill Pfeiffer]

Thank you sir, this is exactly the kind of information I was hoping for!

 

[Ronmar]

Yep, either the control valve is not opening cleanly or the vent port from the pcu thru the floor is clogged. If the system cannot vent below ~5 psi, the wheel valves will stay open and empty the tires.

the sound under the truck is tire air escaping thru the fromt dump valve on pax side of transmission and rear dump valve over/ behind rear axle…

check the pcu vent line, sometimes insects clog the port thru floor behind the grill.

 

[Bill Pfeiffer]

Yep, either the control valve is not opening cleanly or the vent port from the pcu thru the floor is clogged. If the system cannot vent below ~5 psi, the wheel valves will stay open and empty the tires.

the sound under the truck is tire air escaping thru the fromt dump valve on pax side of transmission and rear dump valve over/ behind rear axle…

check the pcu vent line, sometimes insects clog the port thru floor behind the grill.

I don't see a vent line, but there is a brass poppet valve in the face of the PCU that vents vigorously when I turn the power off. I'm guessing this is the updated version...

 

[Bill Pfeiffer]

The only way that can happen (all four tires dump to wheel valve minimum), is for there to be air pressure in the control line from the PCU to the QRV's. Which means the spool valves in the PCU are sticking and letting wet tank air get into the control line keeping it at some pressure above the wheel valve close point - which is typically about 5 psi. That will cause the tires to vent.

Another thing that causes this is a plugged vent between the PCU and the cab bulkhead fitting. Mud wasps are often to blame. On later trucks this was deleted in favor of a simple vent on the side of the unit instead of being plumbed to the cab floor.

Rebuild the PCU after verifying that the vent isn't plugged.

Are there rebuild kits available for the PCU, or is it just a selection of orings and such?

 

[Ronmar]

The brass poppet is a pressure regulator. that's how the system deflates. it opens the deflate solenoid and sends system air to that 6.5 PSI brass relief valve. in this case it acts like a regulator and drops the system pressure to just above the wheel valve closing pressure to allow maximum air to flow back out of the tires thru the quick release dump valves. You shouldn't be getting any air out of that unless the system is commanding a deflate... but the PCU uses pilot operated valves(small air control from the solenoid move a much larger volume sliding spool core) and they can do strange things if all the ports are not clear.

the PCU manifold vents to atmosphere thru the normally open control solenoid valve. to start a cycle the controller energizes control to seal the system, then it gives a shot of supply to pressurize the system which opens the wheel valves. then it looks at the pressure sensor(above that brass poppet) on the PCU to measure tire pressure. when done or shut down, The control valve vents into the black or grey plastic cover at the bottom where the solenoid coils are located. there should be a fitting and hose attached to that plastic cover that runs to the floor, or it has a vent fitting attached to that plastic cover.

That's the line you need to insure is clear, because if it cannot vent the system to zero immediately, the wheel valves may stay open and the flow out from the tires will provide enough flow thru the restriction to keep the system pressure above the wheel valve close point and keep the tires deflating.

Superman had rebuild kits for the PCU core valves.

 

[GeneralDisorder]

This is the kit for the PCU:

New Spicer Air Presure Relay Valve Kit CTIS M923A1 Dana Eaton Pneumatic | eBay

Military M923A1. Parts Kit, Relay Valve.

www.ebay.com

 

[Bill Pfeiffer]

This is the kit for the PCU:

New Spicer Air Presure Relay Valve Kit CTIS M923A1 Dana Eaton Pneumatic | eBay

Military M923A1. Parts Kit, Relay Valve.

www.ebay.com

Thank you sir!