Ctis 94 lmtv

[m-35tom]

The 94 is a single channel system? My front and rear seem to do things independently of each other.
Also with the HGY mode set the engine fan cycles in cold weather with a cold engine, wet tank losing pressure?

 

[Ronmar]

It should be single channel. For the independent operation, have you checked that all three solenoid valves on the PCU are operating properly? While playing with the valve opertion on mine I was able to get the front to deflate by itself/at a higher rate than the rear...

well the fan air does come from around the PCU, but that does sound weird. Do you have leaks in the CTIS system? It should check the air every 15 but is it having to dump a bunch of air in every 15?

The fan is controlled by a thermal switch in the upper radiator pipe right above the fan. If it is cool enough this may be normal cycling, and an indication that you may need to block off some of the radiator surface...

 

[tennmogger]

The CTIS and fan air do share a common source, the wet tank. Air for both must make it through the protection valve, that 'regulator' looking thing on the rear side of the wet tank. So if air is lost in the CTIS then the wet tank will deplete and the fan turns on.

Because the Protection Valve is in line, the wet tank only has to drop to 70 or 80 psi to turn off the air supply to ctis and fan (not priority circuits).

A guage on the wet tank is a great diagnostic tool. Hint, a 't' fitting at the tank can provide a place for an air quick coupler, into which a test gauge can be plugged. If you install NPT swivel fittings you can do future work on that pipe/fitting assembly with much less pain.

On the discrepancy of operation between front and rear systems, a bad Quick Release Valve can do that. If one is bad, the front and rear dump air at different rates and retain different pressures. When 'dump' mode ends, the system tries to read pressure but the front and rear are equalizing through the wheel valves and the pressure is changing. The CTIS won't like the changing pressure and tries again. This continues and a lot of air is wasted.

Thats my understanding anyway.

Being a cold morning is a strong hint. A CTIS air seal in one of the axles may be prone to leak when cold.

 

[m-35tom]

Another clue is that the air used when inflating starts strong but very quickly slows down, like a restriction on the source side of the air. If I just turn the power switch on the rear often tries to deflate without the front. RF tire has leak so every few days it is lower than the rest.

 

[Coffey1]

Run idle up to 1000rpms and the tires will fill quickly

 

[Ronmar]

Yea, fill at idle is pretty slow. Mine fills the same way, The pressure reading at the PCU falls off pretty fast to, I am assuming, the protection valve set point. Then you only get whatever volume the compressor is delivering above the protection valve pressure. Big tires... Havnt monitored wet tank pressure while filling might be interesting to watch.

what is the engine temp gauge looking like when the fan is cycling?

Quick check to see if the fan cycling is CTIS related, take it for a drive and duplicate it, then stop, shutdown and disconnect the CTIS. Restart and drive some more and see if it is still doing it...

 

[Coffey1]

Fan in cold weather takes forever to come on even using ctis. Mine comes on right at 200 mark runs about a minute and shuts down. And stays off for good while.
I drove to rally at 62mph @ appoxmently 45 degrees and fan did not come on for about an hour. If your fan is cycling that much you have air leaks.
Cab air bags can leak really bad.

 

[Andyrv6av8r]

If you have a leak somewhere so bad that your wet tank pressure drops so much that your fan cycles on then you would have low air warnings on your panel. The PPV pressure to open SHOULD be around 75psi unless someone has been monkeying with it. I installed air gauges off of my wet tanks in the cab in all of my trucks.

 

[m-35tom]

I can find no info on how to adjust the protection valve. The supply to the PCU is very slow to build pressure, I need to allow everything to stabilize and then open the supply port to see what the volume is. I cleaned the 3 valves in the PCU but they were not that dirty. Found a big air leak at the LF knuckle, one that would leak a lot or none at all depending on steering angle.

 

[m-35tom]

.

 

[Coffey1]

Bad wheel seal for ctis. Disable ctis until you repair seal.
With power off take connector off ecu.
Check tire pressure. Add air if needed.