CTIS...soo close to working properly

[aw113sgte]

My truck didn't come with a CTIS controller but I found a "probably broken-untested". Plugging it in and it seems to work as it should, electrically at least. I had a missing quick release valve for the front axle, then both hub breathers were disconnected, then found a hub seal leak, then the front CTIS fill line was porous, then the vents for both rear axles were plugged.
Fixed all of those, rebuilt the PCU (well the o-rings and verified the vent was clear), now it fills as it should, but has some issues when deflating. It give me the two solid lights and stops deflating. I know it has a clear vent (actual vent is clear, and the seal on the plastic housing sure wouldn't hold air anyways - not sure if that is important but it doesn't look like it cause cause this issue. I didn't do anything with the relief valve so that's my next place to look as it seems it could cause issues if it is just a little clogged or something. I'm guessing it's the brass almost plug looking part on the side of the PCU? Any other ideas?


Video of failure:

 

[Ronmar]

The brass relief would be the place I would look. When it starts a deflate cycle you should get an initial woosh out of the relief as it vents pressure down to its set pressure(~6.5psi). It will then vent air slow and steady as it purges the air being fed back from the dump valves to maintain that releif pressure inside the manifold...

As with any testing, it is easier to manually control the PCU solenoids with jumpers at the controller connector to monitor PCU operation and look for leaks.

With everything pressurized energizing the dump sol should get a brief woosh from the reliefe and loud steady woosh from the dumps..

 

[Suprman]

If you have an a1 truck, with that black controller you can plug in and see whats going on.

 

[aw113sgte]

The brass relief would be the place I would look. When it starts a deflate cycle you should get an initial woosh out of the relief as it vents pressure down to its set pressure(~6.5psi). It will then vent air slow and steady as it purges the air being fed back from the dump valves to maintain that releif pressure inside the manifold...

As with any testing, it is easier to manually control the PCU solenoids with jumpers at the controller connector to monitor PCU operation and look for leaks.

With everything pressurized energizing the dump sol should get a brief woosh from the reliefe and loud steady woosh from the dumps..

It does sound like it's working properly, the controller just doesn't like that a pressure is slightly out of bounds on the relief valve. Atleast my best guess at this point. Manually actuating all the solenoids, all are functioning properly best I can tell.

 

[aw113sgte]

If you have an a1 truck, with that black controller you can plug in and see whats going on. View attachment 906858

Getting a new software and hardware to do that is on my list of things to do, still waiting for my title and registration to process through before I spend more money though

 

[Ronmar]

That doesn’t sound like a very aggressive deflate. it looked like it ran a full deflate cycle then faulted as it checked pressure. If that relief were partly plugged, it would not vent the manifold down to that low 6-7 PSI. The dump valves dump based on pressure differential, if the relief didn't drop the manifold pressure as low as normal, the dumps would not vent air as fast And the controller might not see what it is expecting to see when it halts the dump to check tire pressure.

You can just hear the dump valves slowing down near the end of this video, as the manifold pressure increases when I de-energize the dump solenoid, before I give it a shot of air to halt the dump.

 

[aw113sgte]

Checked the relief took it off and manipulated it, it's in great shape, no clogs, moves freely. The system does deflate the tires quite quickly and quick release valves seem to work as intended.

1) Faulty PCU relief valve - Checked and as far as I can tell this is good to go.
2) Leaking upper control lines - Doesn't seem likely as all tires are dropping pressure about equally and seemingly quickly.
3) PCU internal leaks - it's always possible...everything looked in great shape though.
4) Deflate solenoid poppet stuck in non-energized position - since it does deflate I don't think this is the problem
5) Poor ground connection to PCU sensor or faulty sensor - Need to look around and see if I can find the sensor specifications to check manually, although when filling it does hit very close to the 55psi pressure target for highway.

 

[Ronmar]

Checked the relief took it off and manipulated it, it's in great shape, no clogs, moves freely. The system does deflate the tires quite quickly and quick release valves seem to work as intended.

1) Faulty PCU relief valve - Checked and as far as I can tell this is good to go.
2) Leaking upper control lines - Doesn't seem likely as all tires are dropping pressure about equally and seemingly quickly.
3) PCU internal leaks - it's always possible...everything looked in great shape though.
4) Deflate solenoid poppet stuck in non-energized position - since it does deflate I don't think this is the problem
5) Poor ground connection to PCU sensor or faulty sensor - Need to look around and see if I can find the sensor specifications to check manually, although when filling it does hit very close to the 55psi pressure target for highway.

Ok, that was one of my other questions, does it fill to the correct pressure. It uses a 0-5v 0-100PSI sensor. It has 3 wires. It gets ground and 5VDC from the controller and it returns 0-5v to the controller based on the pressure it sees.

when you were working on the PCU did you remove the sensor? It is usually considered poor form to install this type sensor pointin straight up like they did as they can collect moisture and debris in the sensor that can effect operation…

When you were manually testing the solenoid valves, if you closed control and gave a shot of air to pressurize the system, you would have known pretty quickly if you had any significant leaks. As soon as the air pressure in the truck side of the system leaks below tire pressure, the dumps will start to vent tire pressure to match the truck side system pressure.

When I pressurize the system, the first place I go and look at are the vent horns on the dump valves(beside trans and over rear axle). If there is ANY air coming out the vent horns, then you have a leak somewhere…

 

[aw113sgte]

Ok, that was one of my other questions, does it fill to the correct pressure. It uses a 0-5v 0-100PSI sensor. It has 3 wires. It gets ground and 5VDC from the controller and it returns 0-5v to the controller based on the pressure it sees.

when you were working on the PCU did you remove the sensor? It is usually considered poor form to install this type sensor pointin straight up like they did as they can collect moisture and debris in the sensor that can effect operation…

When you were manually testing the solenoid valves, if you closed control and gave a shot of air to pressurize the system, you would have known pretty quickly if you had any significant leaks. As soon as the air pressure in the truck side of the system leaks below tire pressure, the dumps will start to vent tire pressure to match the truck side system pressure.

When I pressurize the system, the first place I go and look at are the vent horns on the dump valves(beside trans and over rear axle). If there is ANY air coming out the vent horns, then you have a leak somewhere…

Awesome, that give me a few things to check out. No I didn't remove the sensor but knowing that data I can bench test it. I know I have some very small leaks on the wheel valves I haven't rebuilt but they are very slow (tiny bubbles slowly forming).

 

[Ronmar]

You should be able to probe the sensor wires to see ground, 5v from the controller and whatever the return voltage the controller is seeing coming out of the sensor. Of course it needs a good wiring path between controller and sensor…

 

[aw113sgte]

You should be able to probe the sensor wires to see ground, 5v from the controller and whatever the return voltage the controller is seeing coming out of the sensor. Of course it needs a good wiring path between controller and sensor…

Do you know if that sensor is gauge pressure or atmospheric? I get .553V with no pressure in the system, truck off. If atmospheric I should have .739V for my elevation. If gauge, that means there could be pressure on the sensor, faulty sensor, or we don't have the correct scale for the sensor. I'll have to pull out the PCU to remove that sensor, don't have the time for that today.

 

[Ronmar]

I believe they are absolute so at .05v per PSI, 14.something psi atmospheric pressure should yield .7 something volt return.

Dont forget garbage in=garbage out.
Those voltages above assume a proper 5.00v input. A different input would yield a different response per pound when divided by 100...

 

[aw113sgte]

I believe they are absolute so at .05v per PSI, 14.something psi atmospheric pressure should yield .7 something volt return.

Dont forget garbage in=garbage out.
Those voltages above assume a proper 5.00v input. A different input would yield a different response per pound when divided by 100...

For sure on proper input. I tapped the wires so reference voltage was being supplied by the controller.

 

[aw113sgte]

Wonder if the CTIS unit I bought is programmed for a different relief pressure? Anyone know what that additional sticker means?
This was for an lmtv and I have a MTV so there are 3 dump valves vs 2....wonder if there is a programming difference causing the issue.

 

[Ronmar]

Well a 24p manual might show you if there is a difference in part numbers on the PCU components between the different trucks. I would not think there would be though, as the relief pressure really needs to be that low(just above the pressure that opens the wheel valves) to deliver the fastest deflate.

There shouldn't be that much difference, especially dumping… The dump valves are remote pressure regulators. They simply copy whatever pressure is applied to their input onto their output. Since each axle has its own dump valve, it shouldn't matter how many axles, as 2 axles should deflate as fast as 20 axles would

now timing could be an issue when filling, as it would take significantly longer to fill 3 axles over 2 axles, but I doubt this as CTIS has no idea what the compressor output is, so I suspect it is OK seeing positive pressure changes at each check…

it faulting right after a deflate cycle does indicate that the controller is not happy with the pressure feedback, either the pressure is not right, or the sensor feedback is not right… if you google the relief part number one of the NSN suppliers like part target may have the detailed specs showing what its relief pressure is supposed to be. You will have to measure PCU pressure to confirm what presure that relief is holding thue PCU at during a deflate cycle… then confirm the sensor is returning the proper voltage for that pressure atmospheric +7?

you already have indications that the sensor may not be reporting properly…

 

[aw113sgte]

Well a 24p manual might show you if there is a difference in part numbers on the PCU components between the different trucks. I would not think there would be though, as the relief pressure really needs to be that low(just above the pressure that opens the wheel valves) to deliver the fastest deflate.

There shouldn't be that much difference, especially dumping… The dump valves are remote pressure regulators. They simply copy whatever pressure is applied to their input onto their output. Since each axle has its own dump valve, it shouldn't matter how many axles, as 2 axles should deflate as fast as 20 axles would

now timing could be an issue when filling, as it would take significantly longer to fill 3 axles over 2 axles, but I doubt this as CTIS has no idea what the compressor output is, so I suspect it is OK seeing positive pressure changes at each check…

it faulting right after a deflate cycle does indicate that the controller is not happy with the pressure feedback, either the pressure is not right, or the sensor feedback is not right… if you google the relief part number one of the NSN suppliers like part target may have the detailed specs showing what its relief pressure is supposed to be. You will have to measure PCU pressure to confirm what presure that relief is holding thue PCU at during a deflate cycle… then confirm the sensor is returning the proper voltage for that pressure atmospheric +7?

you already have indications that the sensor may not be reporting properly…

Unfortunately without sensor specifications I'm guessing on proper sensor voltage. Heck the 0-150 sensor is .5-4.5V for the recommended versions. Being that my sensor does inflate the tires to 55psi on highway that makes me think it may be okay but it's possible low pressure readings are not accurate. There are diagnostics I can run with the software but I don't have that yet.
The pressure relief valve looks like it can actually be adjusted but since it's causing valves to dump I'm not throwing that variable in the pot.
Next steps - visually watch relief during deflate, spray PCU with soap to check for leaks, pull sensor and inspect for crud in orifice. If all that checks out I'll plumb in a pressure gauge at sensor. If none of that indicates anything I guess I'll swap in one of those known good "high pressure sensors 0-150 psi" to see what happens.

Interestingly, the LMTV and MTV have different part numbers for the pressure transducer - 673221, 676505 respectively. The relief valves are the same part number. EDIT: part numbers are compatible, found this cross reference:



No luck finding any pressure/voltage specs on it though. NSN 6695-01-509-9496

 

[aw113sgte]

Checked the sensor, had some gunk, also inspected all orings in the PCU. Reassembled everything and same error.
Did check the relief valve while functioning and it appears to be correct as pushing or pulling on the plunger resulted in less dump valve air release. One time the controller continued deflate on it's own but after that it kept erroring out.
Checked sensor to ensure it varied voltage at low pressures and it did. I'll try another sensor next, unless I get the setup to communicate with the controller.

 

[Ronmar]

I dont think the troubleshooting guide goes as far into it as you have. They the assumw the controller is ok, so they say If 5v from controller is ok, replace the sensor.

Was recently helping someone with a failure and worked our way to the pressure sender also...

 

[aw113sgte]

Haven't found any actual manufacturer specs on the pressure sensor. So I picked up a Dearborn interface. Pretty nice software that Spicer made for the CTIS. Atmospheric pressure is reading 14.0 and it should be reading about 14.6 per my location. On deflation is reading about 5.5 PSI and it should be reading about 8 psi, the 8 PSI is per the reference documentation for the part number of the relief valve. Looking through the Spicer documentation for troubleshooting it states it needs to be within one PSI. That's likely where the error is coming from. Unfortunately this does not indicate that the pressure sensor is bad or the relief valve is bad. Obviously the pressure sensor is not reading quite accurately, but that doesn't mean they relief valve can't also be incorrect.

 

[Ronmar]

Mine runs about 7PSI when deflating. 5.5 seems a bit low and closing in on the point where the wheel valves close… If you held a little pressure on that relief with your fingertip, you should see an increase in that deflate pressure…