LMTV CTIS Question

[Suprman]

Just unplug the controller for now

 

[lrholding]

Yep, thats the way I have been running it.

 

[coachgeo]

...New to site, so not sure if we should have this conversation off of this thread????

Keep it here.... we are all selfishly learning along with you and others who come along in the future to read this will learn too.

 

[Stellaevil]

Two things can cause the wheel valves to dump air when trying to inflate. The pressure between the PCU and top of the QRVs is not getting above the tire pressure. Big line leak, pressure switch failed closed allowing the system to function with too low of supply air. Second if there is a big tire imbalance and the pressure switch is opening frequently the pressure in the higher tires will dump but only when the switch is open. The lower lines and air seals are fed by the tires when they wheel valves are opened for inflation, air-leaks in this part of the system cause slow inflation's and tire pressure imbalances not air dumping out the QRVs. The Run Flat light coming on warns of large imbalances in the tire pressures but can be caused by a leak in the upper control line from the PCU to QRVs.

 

[lrholding]

Stellaevil, thanks. I never could find any discussions or information about HWY and RUNFLAT flashing at the same time. I assume a faulty QRV could cause this?

 

[Awesomeness]

There is a CTIS controller manual posted around here, and I think it has all the flashing error codes in it.

 

[Stellaevil]

Stellaevil, thanks. I never could find any discussions or information about HWY and RUNFLAT flashing at the same time. I assume a faulty QRV could cause this?

QRVs are pretty bullet proof. Run Flat light is looking for large tire pressure imbalance >30 to 50% but a upper air line leak can fool the system into thinking it has the imbalance.

 

[Stellaevil]

There is a CTIS controller manual posted around here, and I think it has all the flashing error codes in it.

www.steelsoldiers.com/showthread.php?175911-Central-Tire-Inflation-System-(CTIS)-AXTS-0015-2018

 

[lrholding]

Should be able to get back to working on this later the week, will let ya know what I find.

 

[wandering neurons]

Thread hijack - CTIS issue... My M1081 didn't have a CTIS ECU in it when I got it last year. I installed one, but system isn't working right (why would I hijack this thread otherwise).
I'll have to check when starting the engine normally. But when putting shop air at 125 psi into the Emergency front glad hand, hitting the master-power switch on the dash, brake pressure gauges show 120 psi: ECU powers up with flashing HWY light. HWY light flashes twice, then all five lights start flashing simultaneously. I've tested the wet tank pressure switch and wiring, it opens and closes correctly, as checked on the ECU plug in the cab. I've replaced all three solenoids on the PCU, two were bad. Six-pin PCU plug ohms out correctly.
I get no "burp/pressure test" from the PCU except when I power-off the master switch, and it does this whether the ECU is plugged in or unplugged. I've got good pressure to the supply line at the PCU.
I get no noises under the cab at all (other than some leaky rear brake chambers, that's next to fix).
I've used electrical contact cleaner on all connections.
I've pulled the PCU again, am going to disassemble and test the solenoids and valves electrically and mechanically..
So, over to the experts - thoughts on anything else besides ohming out wires? I can't see any way to test the three-pin PCU switch.
Thanks!

 

[wandering neurons]

double-post

double-post - ignore

 

[coachgeo]

Thread hijack - CTIS issue... My M1081 ....

A0 or A1?

 

[wandering neurons]

A0 - "Classic LMTV" M1081 from Ft. Bragg. Small rear air chambers too, but that's a different post...

A0 or A1?

 

[Stellaevil]

If the system comes and flashes Highway one time and then 5 lights without checking the tire pressures it doesn't like the atmospheric reading from the pressure sensor on the PCU. Connector pins, wiring, the +5 volts from the ECU. There is a link to the manual a couple of posts back.
If the system comes up flashing the highway light and then the PCU cycles once and the 5 lights start flashing...the system did not get a good tire pressure reading it was below 5psi. Large air leaks in lines or the inner axle air seals. The pressure check only lasts 2-3 seconds so you can only check for air leaks during the check.

 

[wandering neurons]

Actually, I get two flashes from the HWY light before all five start flashing.

I disassembled my PCU this evening with the following results:
Used two 12v batteries in series for 24v and tested the three solenoids - all clicked as expected. Shorted my test leads momentarily and got a nice flash. I was quick enough that nothing got scorched other than my pride. Lots of energy in RV batteries.
Split the aluminum PCU block and tried pushing on the three poppet valves. One pushes in and pops up freely, two don't, and the worst one is in the middle position. Which is think is the deflate valve and appears to be internally plumbed into the PCU sensor. I was able to pull out all three poppet spools and test by feel. Two of them do not freely move up and down in the spool, but seem to stick in the down position. Was able to disassemble the worst, tried cleaning the bore but the valve but there is still a lot of "sticktion" between the poppet and the outer spool. I'm now thinking that the rubber/Viton ring has gone from round cross section to rectangular, and hanging in the bore. And when this happens during ECU/PCU test, fails the system.
Which if sticking open, could explain why I get a "burp" from the PCU when I power the truck off even with the CTIS ECU disconnected.

Questions for the experts now: Am I barking up the wrong tree thinking that the spool valves are sticking open or possibly on the right path? Has anyone dug this deep into a PCU?

I still need to ohm out wires, but will be traveling next week. Had the truck very stuck in the muddy yard and want to get CTIS working...

Thanks!

If the system comes and flashes Highway one time and then 5 lights without checking the tire pressures it doesn't like the atmospheric reading from the pressure sensor on the PCU. Connector pins, wiring, the +5 volts from the ECU. There is a link to the manual a couple of posts back.
If the system comes up flashing the highway light and then the PCU cycles once and the 5 lights start flashing...the system did not get a good tire pressure reading it was below 5psi. Large air leaks in lines or the inner axle air seals. The pressure check only lasts 2-3 seconds so you can only check for air leaks during the check.

 

[Suprman]

There used to be rebuild kits for the m939a2 ctis valve body. I think it had new poppets and o rings. Maybe something available for the lmtv.

 

[wandering neurons]

Interesting! Though the M939A2 -24P-2 shows two different valves: two of one, one of the other part number. I found a kit on a well-known auction site and ordered same. Will report when I receive it and reassemble. Again,thanks for the support here and there.

There used to be rebuild kits for the m939a2 ctis valve body. I think it had new poppets and o rings. Maybe something available for the lmtv.

 

[Coffey1]

You can make a 939 series pcu work in a Lmtv.

 

[DiverDarrell]

For what it’s worth, my ctis has been a central tire deflation system for a long time. I finally got around to working on it and found when it would go into a deflate cycle it wouldn’t stop until the truck was off and tanks drained, also had 5 flashing lights. I took the pcu apart, cleaned it all up and re installed to only find the same issue. Under a hunch I went and took the vent line off the pcu, and bug guts flew out as the line depressureized. Pressure in a vent line, clogged due to bugs. With the vent line off, ctis works great! For now that is.

 

[wandering neurons]

Vent line is a easy check, can try the PCU without it connected, or just push air through the line from compressor. Thanks for input.

Coffey1, also good to know about interchange, will keep that in mind if needs must

For what it’s worth, my ctis has been a central tire deflation system for a long time. I finally got around to working on it and found when it would go into a deflate cycle it wouldn’t stop until the truck was off and tanks drained, also had 5 flashing lights. I took the pcu apart, cleaned it all up and re installed to only find the same issue. Under a hunch I went and took the vent line off the pcu, and bug guts flew out as the line depressureized. Pressure in a vent line, clogged due to bugs. With the vent line off, ctis works great! For now that is.