M923A2 CTIS gives not more than 45PSI to the tires

[engele]

Hi together

i had my first weekend trip yesterday with my A2. Not long, only 50km.
The Beast swing sometimes. If i start the truck the tires fill up (one or two tires lose air if it´s longer as a week not startet).
But the the HWY lamp flash and show that it fill or try to fill. After 1 hour the HWY AND XS-C lights the hole time!
If i push the XS-C buttom the truck release air and the XS-C light constantly.
I checked the air pressure in the tires after i pushed the HWY buttom (flashs only the hole time and show that he fill up) and wait 30 minutes, the tires have only about 45PSI and goes not higher. If i shut off the truck i can fill it manual up to 80psi.
My air pressure instruments in the cab go up to 120-130PSI. The compressor can not be the problem.

I filled up the both front tires up to 85PSI manual now and wait till today afternoon, check the pressure again and start the engine. I think the pressure will go down with the running engine and pressed HWY button down to 45PSI agian.

Can i adjust the pressure? Or an other idea? Can´t find something in the manual!
Hope you can help me.
Best regards Alex

 

[MtnSnow]

First off. DO NOT manually "overfill" a tire(s) from the Hwy setting (usually around 60psi) as what happens the CTIS does a pressure check and see's tire(s) higher than needed and sends out the deflate signal the problem is it will also deflate the tire(s) that are/were at the correct pressure and you help create a viscous cycle in the system chasing correct pressures.

The reason your CTIS ended up showing the XC & Hwy lights is the system "timed out" trying to get to Hwy pressure. All that needed to happen is a re-press of the hwy button to allow the system to start trying to inflate.

If you can find someone with the spicer/dana programming tool you can have them set new tire pressure settings.....but good luck on that! I still haven't found anyone with one....Including the local NG unit near me.

 

[engele]

mmmmhhhh. In HWY mode only 60psi? it´s not a lot.
I tried to push the HWY button again if the XC & HWY lights are showing. They flash and try to fill the tires, after 30 minutes both lights stady again. Pressure is to low (about 40-45) and the truck/tires swing.
I think it´s not possible to find someone with this tool here in south of Germany (( ! To find one with special tools for an Unimog oder Man is not problem. But the M939´s a very rare here.

 

[Suprman]

Did you clean the catch filter on the air feed to the ctis valve body? Its possible the pressure transducer is bad and telling the system you have reached 60psi when really there is only 40. You could also have several small leaks that can confuse the system but not big enough leaks to fault the unit on initial pressure check.

 

[Coffey1]

I have two ecu and they are both set at 55 psi

 

[MtnSnow]

http://connection.ebscohost.com/c/a...es-5-ton-trucks-ctis-updates-highway-missions

Newest settings are 90 psi for M936A2 wreckers and 70 PSI for all other M939A2 models

As you can see from the attached PDF they also mention that 60 psi was the prior CTIS setting for the non-wrecker models of the M939A2 trucks.
View attachment PS_Magazine_Issue_726_May_2013 - Page 8 & 9.pdf

 

[Suprman]

This is a recent model ecu

 

[engele]

Hi,
i disconnected the ctis at the rims and filled up to 80psi and drove. A new car, no Swings, and faster!
I know that 2 rear rims have Problems that they are empty after a week. I will Chance the o-rings in the two rims first and try it again. I thinked if they have Problems at the rear Tires, they fill up the front ones complete or not?
First thanks to all for the help and support! I will give you an update in the next days after i change the o-rings.
best regards alex

 

[MtnSnow]

While you have the rims broke down to do the O-rings also make sure that the turret valve (valve stem) is tight as these seem to get loose pretty often as well.

 

[Coffey1]

70 and 80 lbs will that bounce you right out of the road if you hit a good bump in road