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M1083 dumping air

U

Ultra Mag

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Culpeper VA
rolled cab over today to fix water pump. started it up to see if it leaks water. Right away it started dumping air , ctis HWY light flashing. help please thanks.
 
R

Ronmar

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Dumping air from where exactly? If it is CTIS, the dump and wheel valves are controlled by air pressure. It takes a certain amount to open the wheel valves(6-7 PSI). The dump valve is basically a remote pressure regulator. When you decrease pressure on the supply side of the valve the valve dumps tire side pressure to match. So a leak or valve issue around the PCU could cause ALL the dump valves to activate. So where is it dumping air from.

The best way to troubleshoot CTIS is to connect shop air to the emergency gladhand in front so you can look for leaks without the engine running. Chock the wheels as applying air there also releases the park brake...

If it is the controller causing it, simply unplugging the controller should stop the dumping.
 
U

Ultra Mag

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Culpeper VA
Ronmar said:
Dumping air from where exactly? If it is CTIS, the dump and wheel valves are controlled by air pressure. It takes a certain amount to open the wheel valves(6-7 PSI). The dump valve is basically a remote pressure regulator. When you decrease pressure on the supply side of the valve the valve dumps tire side pressure to match. So a leak or valve issue around the PCU could cause ALL the dump valves to activate. So where is it dumping air from.

The best way to troubleshoot CTIS is to connect shop air to the emergency gladhand in front so you can look for leaks without the engine running. Chock the wheels as applying air there also releases the park brake...

If it is the controller causing it, simply unplugging the controller should stop the dumping.
Click to expand...
Ronmar said:
Dumping air from where exactly? If it is CTIS, the dump and wheel valves are controlled by air pressure. It takes a certain amount to open the wheel valves(6-7 PSI). The dump valve is basically a remote pressure regulator. When you decrease pressure on the supply side of the valve the valve dumps tire side pressure to match. So a leak or valve issue around the PCU could cause ALL the dump valves to activate. So where is it dumping air from.

The best way to troubleshoot CTIS is to connect shop air to the emergency gladhand in front so you can look for leaks without the engine running. Chock the wheels as applying air there also releases the park brake...

If it is the controller causing it, simply unplugging the controller should stop the dumping.
Click to expand...
 
U

Ultra Mag

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Culpeper VA
OK my bad its a 96 M-1081 with 3116 . hoked up clad hand no sound of air, unhooked then started, no air dumping now, ctis hwy blinking,20 min later air up to 50psi hwy light solid now. everything seems normal now but would like more psi
 
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Ultra Mag

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Went back out started truck same thing again hwy flashing dumping from valve in back right in front of pintle hitch nut, disconnected ctis it stopped dumping. Pluged ctis in stopped dumping
 
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Ronmar

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The front dump valve is beside the transmission, passenger side. The rear dump valve is on the back side of the frame crossmember behind the rear axle. Both these valves receive the same control air pressure from CTIS so if that valve only is shifting to dump, it probably has a problem like debris in the valve causing it to shift/stick in the dump position inappropriately. I would pull it apart and clean/inspect it to decide wether it needs to be replaced.

I should have mentioned when you apply shop air to the emer gladhand, it has to be above the 115 PSI switch pressure of the ctis sw on the wet tank. CTIS wont do anything untill that switch closes and tells it the wet tank is near full pressure. That sw opens around 89 PSI to tell CTIS it is out of pressure/wet tank is empty. You of course also need to turn on the main sw to power CTIS so it can operate.

Once CTIS sees the pressure sw close, it closes the control valve which seals the PCU(pressure control unit) manifold then it gives a shot of the supply valve to pressurize the system. This passes thru the dump valves and opens the wheel valves. With all the valves open, tire pressure should be seen on the manifold. The controller is looking at that pressure via a sensor on the PCU manifold. An unstable/changing pressure = a leak somewhere or a low tire) If it doesn't see a stable, in-range pressure, it faults. If it sees a stable in range pressure, it will inflate, deflate or do nothing as necessary to reach its commanded pressure. Then it opens the control valve to vent the system and close the wheel valves until its next scheduled pressure check.

Probably the easiest way to raise wheel pressure with a working CTIS system is to replace the pressure sensor on the PCU. The controller dosnt know pressure it is looking for a voltage being returned from the sensor. The stock sensor is 0-100 PSI and returns a voltage based on that span. say 0-5V that with 50 PSI = around 2.5V. If you put in a 0-150 psi sensor, that 2.5V point is now 75PSI(a much better highway pressure for the tires IMO) There is a thread on here somewhere about doing it. It is about a $10 part, plug and play...
 
U

Ultra Mag

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I will pull valve in rear cross member tomorrow to see whats going on hopefully. I will get back to you when done . thanks for your help and Marry Christmas.
 
U

Ultra Mag

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I will get back on it once I get back up and running. had to order new water pump. Started several times yesterday trying to find leak with no dumping issues.
 
R

Ronmar

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Port angeles wa
Coffey1 said:
I had a 939 that was only dumping rear because of pcu dump valve
Click to expand...
That would be weird... the quick release valves are controlled by air pressure(basically remote controlled regulators) and they should all see the same air pressure coming from the PCU. The dump valve in the PCU connects the manifold to a 7PSI relief valve on the side of the manifold and is normally closed. You can see this relief on the PCU near the pressure sensor. The dump valve sends air to that relief which acts like a regulator to lower the manifold pressure to around 7-8 PSI(Just enough to keep the wheel valves open).

The qr valves for each axle see this pressure drop on the supply side and dump air out of the vent from the tire side to try and match it. One QR venting in this situation would still indicate a QR valve problem...
 
Coffey1

Coffey1

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Could be all I can tell you is it was dumping from rear only.

Took pcu apart cleaned and replaced bad dump solanoid problem solved.
 
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