New CTIS issue on a trip.

[aw113sgte]

CTIS is set at 85 PSI on an MTV, after filling and the light going solid, the quick release valve going between the front axle and the two rear axles, the one that's mounted next to the transmission on the frame rail, remains open draining the front tires down a bit before it closes. This resulted in the rears being up to 95 PSI in the front's being 82 PSI.
Seems to me like the quick release valve is faulty and draining pressure from the front side when it should be closing after filling. It was doing this the other day but there was only a few PSI difference, was a little colder and now It's much more significant difference. All tires on every axle are perfectly balanced left to right side.
Only other thought is possibly an obstruction in the line causing the quick release valve to see a pressure differential due to the flow.

Any thoughts? I have removed the filters in the wheel valves. System's been working perfectly up until this point.

 

[GeneralDisorder]

You have a partial blockage - if it's both front tires then it's probably between the QRV and where it splits to go to either front wheel. The pressure between the QRV and the tires is not dropping off to below 5 psi to close the wheel valves. At higher pressures you need more flow and if you have a partial blockage then it will drain down to where the reduced flow can drop the pressure below 5 psi and close the wheel valves. That's the dump you are hearing after it does a pressure check.

Remember that the only way the QRV can vent tire pressure is if the wheel valve is being held open. And that can only happen if the valve is faulty or there is non-zero pressure being held against it from the chassis side. Since you have two that are draining down to the same pressure I give the probability of the wheel valves actually being the culprit very little chance. And the QRV is just doing what it's designed to do - vent air coming from the tires.

The QRV is VERY simple. You can remove and clean it but it's not likely to be your issue.

I suppose it's possible that the line to the QRV is holding some pressure and keeping just that one QRV open..... but since it's not affecting the rear I think that's unlikely and the entire system from the PCU to the QRV's is just a single line.

 

[Ronmar]

I agree, sounds like it is probably a blockage/restriction. The line from the PCU comes down to a T behind the transmission and splits to feed the input of the front and rear axle QRVs

The QRVs are simply remote pressure requlators. Using a sliding core like a 2way check valve, They match whatever is on their input to their output, by feeding input across to output when the core is pushed that way, or returning output to input AND venting output down to match input When the core is pushed the other way until the pressures equalize or drop low enough to close the wheel valves/source…

same kind if thing can happen with a clogged PCU vent line. The system pressure cannot drop below the wheel valve close pressure. So the QRV/dump valves on all axles continue to dump and can feed back enough pressure thru the QRV’s to keep the system above wheel valve close pressure And continue to vent with the wheels supplying the air.

if the core on the front axle QRV beside the transmission slides OK, you could swap it with a rear axle valve and see if the issue moves to a different axle. If the problem moves, its the QRV if the problem stays on the front, then it is an issue with the connection to the front axle QRV…

 

[aw113sgte]

I'm remembering when I got the truck this QRV was missing...there was a mud dobber nest in the tube going to the front. I pulled out the dirt and flushed it out but maybe the remaining crud screwed up the new valve (old valve from Midwest)

 

[GeneralDisorder]

I'm remembering when I got the truck this QRV was missing...there was a mud dobber nest in the tube going to the front. I pulled out the dirt and flushed it out but maybe the remaining crud screwed up the new valve (old valve from Midwest)

Pieces of it are probably still lodged somewhere in the line before (wheel side) the QRV. This is a flow issue holding the wheel valves open not a QRV issue in my opinion.

 

[Skyhawk13205]

Do your tires take a while to air down where you get the in between mode error? My truck has the same problem but does it when it is cold, I think it makes the wheel valves more sensitive to unbalanced flows. I think I have an obstruction in the lines or in the rear axle CTIS hub port causing a differential flow causing wheel valve to stay open. When it gets really cold all my tires start doing it, I eventually reactivated my CTIS off switch to keep from draining the tires. When I do my rear seals next summer it will give me a chance to T/S for blockages.

 

[aw113sgte]

I have gotten the "between modes" dual lights before. Wasn't with this situtation.

I went through and checked the QRV - had a tiny bit of crud in it(cleaned it out) but that was it. Took apart the wheel valves and noticed a little silicon grease migrated from the outer lip inward so maybe that was causing a little sticking of the diaphragm. Also swapped out the springs with some less compressed/slightly stronger ones.

System aired up just fine with no issues. Not clear on what was the issue but it's working...for now. Does seem like the m1096 and m1085 would be a bit more sensitive on the front axle as the lines are longer so more restriction and volume. I thought there was a thread where a spicer guy was talking about issues with the longer wheelbase trucks. Listening to the QRVs, I can't tell any difference in the sound - all seem to bleed off pressure at about the same very rapid rate. Before they would do this, but then there would be a lower flow from the front one for a while till it closed.