CTIS Pressures up Light goes solid then drains the tires

[Worldsworstfish]

CTIS problems, tried troubleshooting on my own but have hit a wall.

When I plug in the CTIS and start the truck, the tires will inflate and the Highway Light will go solid. Within 15 seconds of the light going solid I hear solenoids clicking and the system will start venting until the tires are flat. It vents from the rear port and next to downpipe through the fitting I have pictured. If I shut the master off during this venting it will still continue to vent until tires are flat.

I filled up my tires with shop air and they stay up. So I assume that the wheel valves are holding, confirmed by loosening banjo bolts with no air leakage.

I took a wheel valve apart to figure out how it works, and still do t have any idea how it works so my second question is cansomeone explain how it works.

 

[aw113sgte]

That quick release valve looks different than mine, although that could be okay.
When mine continued to vent it was due to leaks to the wheel valve. The hoses had small holes visible when sprayed with soapy water.
There are other things that can cause this though, leaks in pcv for example.

 

[Ronmar]

Ctis closes control to seal the system, then gives a shot of supply to pressurize the system. The dumps are remote pressure regulators, whatever they see on the input they match on their output by passing input to output or venting output down to match input. When output is greater and while it is dumping it also feeds a little air back to the PCU.

when the supply adds pressure, the dumps pass it to the wheels. When the wheel valves see ~5PSI, it pushes the diaphragm out and exposes the passage to the tires. Now tires are tied to the manifold and pressure can be measured, and air added or removed. Supply opens to add air, the deflate solenoid connects the manifold to a 6.5 PSI relief Valve. This acts as a pressure regulator and drops the manifold pressure to ~7PSI. The dumps mimmic this 7PSI to the wheels. It is enough to keep the wheel valves open but Since the tires have more air pressure, air flows back to the dumps and they dump it trying to get it down to the input 7PSI. To stop a dump the controller closes the deflate and gives a shot of air and the system stabelizes at tire pressure.

when everything is done, the controller releases the control solenoid and it vents the manifold to 0, the dumps mimmic this to the wheels by dumping briefly. 0 is not enough to keep the wheel valves open and they close and hold air in the tires.

the control vents into the lower plastic cover on the PCU, it is connected via a line down to a floor port. If the control valve doesn’t open cleanly or If this line or floor port is clogged then the pressure cannot vent low enough to close the wheel valves and the tires will drain. That port thru the floor behind the grill likes to have bugs clog it, have diagnosed a few of these lately…

that pic looks like a normal tire dump/qr valve except it is missing an outlet horn that clips over that large lower opening…

 

[Worldsworstfish]

Ctis closes control to seal the system, then gives a shot of supply to pressurize the system. The dumps are remote pressure regulators, whatever they see on the input they match on their output by passing input to output or venting output down to match input. When output is greater and while it is dumping it also feeds a little air back to the PCU.

when the supply adds pressure, the dumps pass it to the wheels. When the wheel valves see ~5PSI, it pushes the diaphragm out and exposes the passage to the tires. Now tires are tied to the manifold and pressure can be measured, and air added or removed. Supply opens to add air, the deflate solenoid connects the manifold to a 6.5 PSI relief Valve. This acts as a pressure regulator and drops the manifold pressure to ~7PSI. The dumps mimmic this 7PSI to the wheels. It is enough to keep the wheel valves open but Since the tires have more air pressure, air flows back to the dumps and they dump it trying to get it down to the input 7PSI. To stop a dump the controller closes the deflate and gives a shot of air and the system stabelizes at tire pressure.

when everything is done, the controller releases the control solenoid and it vents the manifold to 0, the dumps mimmic this to the wheels by dumping briefly. 0 is not enough to keep the wheel valves open and they close and hold air in the tires.

the control vents into the lower plastic cover on the PCU, it is connected via a line down to a floor port. If the control valve doesn’t open cleanly or If this line or floor port is clogged then the pressure cannot vent low enough to close the wheel valves and the tires will drain. That port thru the floor behind the grill likes to have bugs clog it, have diagnosed a few of these lately…

that pic looks like a normal tire dump/qr valve except it is missing an outlet horn that clips over that large lower opening…

Ronmar thank you for the response, I have read a lot of your posts and really appreciate all of your posts you have written. Was hoping to get a response from you.

Just to make sure that I have things right, the 5psi that the system initially sends opens the wheel valve because the surface area of the diaphragm is so much larger than the small hole coming from the tire. So the PCU puts some pressure in the wheel lines, which allows the wheels to back flow into the pcu. The PCU reads the tire pressure, If the pressure is low the PCU takes air from the wet tank and sends it to the wheels. So during inflation the tires fill because of the pressure difference. To deflate the PCU keeps 7 pounds on the wheel lines to hold open the diaphragm and the wheels being higher pressure the wheels flow back to the dump valves.

Still confused on operation of the dump valves. They can send air to the wheels or they can dump the air to atmosphere. Do they work based on where the higher pressure is? So if they are draining from the wheels the pressure is higher on the wheel side so they dump to atmosphere and when the PCU is sending air to the wheels the higher pressure in on the fill side so they pass the air to atmosphere? The dump valves have no electrical solenoids on them?

So your diagnosis is that after filling the tires initially the CTIS runs a check on the tire pressure, it sends the small amount of pressure to open the valves and then reads the pressure, but the PCU fails to vent the pressure from the wheel valves and the tires deflate.

I will check on the plugged line from the PCU, could it also be a bad solenoid on the PCU if I don’t findline plugged line?
Really appreciate your help will be next week before I have time to check things out.

 

[Ronmar]

On the wheel valves, the air from the truck is fed into a port off to the side of center so fills in that area of most of the inner/inside face of the diaphragm. The outer face of the diaphragm is vented to the atmosphere, and there is a small spring in the center. Anything above 5PSI is enough to lift the diaphragm center off the port to the tire. So anytime the system is over 5PSI, the wheel valves are open. When checking pressure, the PCU sends way more than 5 PSI. If it sent less than the tires have the dump valves would try to match it by dumping. The truck side volume is tiny compared to even one tires volume, so the tires simply absorb it and the system stabilizes at tire pressure. That is why it is important that the tires are all the same pressure. If one is low, once all the wheel valves open the 4 tires will equalize, and this can cause unstable pressure at the PCU, and if it is fluctuating too much the controller will fault.

Yep, thats exactly how the dump valves work, all air manipulation, no electric whatsoever.

yes the PCU must vent cleanly to 0PSI. If it cannot vent the air faster than the tires are returning it, then it can hold the wheel valves above 5PSI and as long as they stay open the dumps will deflate them to the lower pressure seen on the truck side.

a control solenoid that is not opening cleanly/fully could also cause this, but more often than not it is a clogged floor vent pass-thru/port… the quick test for this is to simply disconnect the hose where it attaches to the plastic cover and let it vent directly from there. I have a private discussion going with someone who has this exact issue. He blew the port clean and now his is venting properly. I have a friend with an A1R 6X and they ran out of floor ports so simply vented that lower PCU cover right into the under-dash area…

 

[Worldsworstfish]

On the wheel valves, the air from the truck is fed into a port off to the side of center so fills in that area of most of the inner/inside face of the diaphragm. The outer face of the diaphragm is vented to the atmosphere, and there is a small spring in the center. Anything above 5PSI is enough to lift the diaphragm center off the port to the tire. So anytime the system is over 5PSI, the wheel valves are open. When checking pressure, the PCU sends way more than 5 PSI. If it sent less than the tires have the dump valves would try to match it by dumping. The truck side volume is tiny compared to even one tires volume, so the tires simply absorb it and the system stabilizes at tire pressure. That is why it is important that the tires are all the same pressure. If one is low, once all the wheel valves open the 4 tires will equalize, and this can cause unstable pressure at the PCU, and if it is fluctuating too much the controller will fault.

Yep, thats exactly how the dump valves work, all air manipulation, no electric whatsoever.

yes the PCU must vent cleanly to 0PSI. If it cannot vent the air faster than the tires are returning it, then it can hold the wheel valves above 5PSI and as long as they stay open the dumps will deflate them to the lower pressure seen on the truck side.

a control solenoid that is not opening cleanly/fully could also cause this, but more often than not it is a clogged floor vent pass-thru/port… the quick test for this is to simply disconnect the hose where it attaches to the plastic cover and let it vent directly from there. I have a private discussion going with someone who has this exact issue. He blew the port clean and now his is venting properly. I have a friend with an A1R 6X and they ran out of floor ports so simply vented that lower PCU cover right into the under-dash area…

Ronmor,

Many thanks had time to lookat the CTIS today. You were exactly right. I pushed , out about three inches of some kind of bug (First Picture). One bit of advice for peoplein the future, the place where the vent goes out the cab is the second picture. The third picture is where the vent used to come out of the control box that sectionis plastic use a wrench on both the nut and the 90!

Once the bugs where gone the CTIS worked perfectly! Ran through all thesettings and all work perfectly all the ties were even pressure. I now need to search for the higher pressure sensor trick. Would like Highway mode at 75 lbs or a little higher if I can.

 

[Ronmar]

Oh darn... you can probably glue it... at least it works