Ultimately, I ended up having a burnt out compressor motor, and rather foolishly (however unsurprisingly) had mixed up the RH outlet and supply inlet hoses on the front valve block.
Fix was replace compressor with new Hitachi (NOT hitachi-type) unit, and de-fudge my air line mix up.
Lesson being; always tripple check your work.
See below for the shenanigans.
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Hi all,
So I've been chasing EAS woes for a while now. When I bought the vehicle, it had an aftermarket Hitachi-style compressor that was on its way out. Randomly but increasingly got the "gallery pressure does not decrease when venting to atmosphere" code, to the point where it just would not go away truck has about 150k on it, CA or NV vehicle its whole life, and appeared to have never been driven on anything more fun than a gravel driveway.
Below is what I've done, in sequential order:
-Replaced desiccant in old assembly- slightly clumpy, no minimal dust; no change until my dog stepped on the ride height switch, causing the vehicle to lift. When attempted to lower, front comes down but rear stays high. Code persists.
-Replaced o-rings in all three valve blocks (OEM blocks or very good counterfit) - some silica dust but not an alarming amount; now the compressor will run until ride height switch is pressed, causing gallery pressure does not decrease code. Vehicle sitting below access height. Doors open/closed trick changed nothing.
-Realized that in replacing air lines to central valve block I had flipped the rear valve block and reservoir hoses; got a huge rush of air at the same PSI causing compressor to stop running; corrected this and back to previous state. Doors open/closed trick changed nothing.
-Replaced compressor with used "verified good" OEM unit from a trusted source with roughly 125k miles, replaced desiccant and felt filters; I checked that the pressure coming out of the compressor was strong enough to push past my fingers when placed over the red and blue ports on the dryer. Used unit was significantly quieter than old unit.
-Compressor will engage, run smoothly to about 50psi, then begin to slow. Continues to slowly build to roughly 60psi and cut out, amber warning light on dash with "pressure increases too slowly" code.
-I've checked for leaks at all accessible junctions (ears, eyes and soapy water), replaced the cap on the dryer because the connections were bubbling. This did not improve or deteriorate anything. No other leaks found.
-Monitoring PSI on my Autel (my GAP tool is halfway across the country, don't ask, no I can't get it sent here), pressure rapidly decrease to around 15psi when compressor cuts out, then slowly build to around 70psi. The system would fart, dropping pressure back to around 15-20psi, then slowly rebuild to around 70 without compressor running. This would happen about 3 times, getting slightly slower each time, then hold at about 65psi.
-I pulled the air supply unit connection line (blue connector on air dryer) to see if it was pushing air out of the canister. Instead I got a rush of air from the hose (coming from the central valve block) and after about 5 seconds "pressure increases too slowly" code. Shut the vehicle off, started again, put finger over the hose end and got "pressure increases too rapidly" code.
-Removed compressor and tested for pressure. I used a jobsite compressor gauge, extra 6mm od tubing, hose barb/1/8npt fitting and a coupler to make a test tool. Less than 20 bucks. Use 12v power supply to power the compressor. Motor would die at 120psi, roughly the same as on the truck.

As I mentioned, no I do not and can not at the moment have access to a GAP tool, just my Autel 805, which fortunately reads everything, albeit on a kinda dumb basic display. I know this isn't ideal but it's what I'm working with.
My next thing to try is pulling the compressor out, hooking it up to an external 12v power source, and seeing if it will run continuously and consistently when not hooked up to the vehicle. Hopefully, that will tell me if I need to rebuild the compressor or chase other components. Before you ask; I bought a used OEM unit because I had some unexpected other expenses come up after getting laid off from work.
Normally, I would either buy brand-new parts, or buy and rebuild a used one, but at the time I was working with unforeseen constraints on my budget. That's changed now, but I would rather not spend 500-900 dollars on a brand new Hitachi pump when this one could be rebuilt, or there's another component that needs to be addressed first. I know Land Rovers are not inexpensive to own, but sometimes life just throws you curve *****. Or, all the time, lately.

Thank you all for the wealth of knowledge and inspiration on this forum!

 

Brand new Hitachi come up on Amazon warehouse for about $200 time to time, FYI. Still not super cheap, but at least it is OEM quality. Same for Arnott, which is AMK style. They come up also.

Some things to know:

Unable to vent is generally an exhaust issue on the compressor itself. On the aftermarkets the solenoid that works the pilot exhaust can easily fail or get weak. That solenoid can be swapped.

Gallery pressure should drop by design. That is why the system farts. The compressor can not start if the gallery is under high pressure, it is just too small and weak to fight pressure to initially get going. So a little odd that it sometimes seems to hold ~65psi - that seems a bit high.

During a compressor cycle event, it runs to bring the vehicle to a specified hight and only then will the reservoir open to fill. Once full, the compressor stop and the gallery pressure is dumped. Just an FYI.

The center valve block only has a spot for the pressure sensor to read the gallery. The gallery is the tube from center to front valve block, form the center to rear valve block and the supply line into the compressor all the way to the piston head and exhaust port. The center block in no way controls air from front to rear, etc.

If the gallery pressure is building with the compressor not running, you have a leak at a valve block. Either front, rear or reservoir. Air is coming from somewhere. You could pick up some high PSI (at least rated 300psi) inline 6mm OD push connects. I will link an example, shop around cause I dont think the Amazon ones can hold high PSI. With these you can do simple diagnostics. You can cut and put these inline to the front valve block and rear valve block. Then you can close then when the compressor is not running and observe if pressure is still increasing. So if both front/rears are closed and it does, you know the center block is letter the reservoir dump its air. If not, then you can open the front or rear and observe. It is just a quick and dirty way to diagnose things physically. ALSO, with both valves closed you can run the compressor and see if it gets up to about 200psi. After all you have pretty much isolated everything but the reservoir which during a lift event should not be open to gallery. However you can still read pressure and it should go up REALLY fast. You can also jumper the compressor relay and observe pressure. The compressor exhaust port will blow and pressure exceeds about 280 psi and the excess air will vent out exhaust. You will hear the compressor suddenly sound differnet. Also if you get a third valve installed at the supply line from the compressor you can build up gallery pressure and close it to see if the gallery pressure drops - with that valve closed it should not because the only escape if through the compressor. If it does, you have some sorta external leak at a valve block, damaged line, etc. You can also get end caps to cap off lines if you need to for some reason. 1/4" fitting may work, but 6mm OD is best given the pressures.

So with those things known, at face valve it looks like you have a couple issues. You have air dumping into the gallery from somewhere when not running and need to figure from where.. If the truck is dropping, then it could easily be a strut. This would be a valve block issue. But it also sounds like you also have a performance issue with the compressor. This could be a sticking exhaust plunger or totally worn piston, etc.

I dunno, read some of that and see if you get any ideas that could help. Also you could always get a Schrader push on valve, like a bicycle valve, and fill the system with a shop compressor. Assuming your Auto can manually control valve blocks to open then up and get the air into the struts. It is a way to at least get it up and drivable with fingers crossed there are no major leaks.

For you or anyone interested, heck I should pick up a couple, this is the ideal ball valve - a type 6560. These are all metal and can take a lot more PSI, almost 300:

https://www.ebay.com/itm/174833740124

 

Dude. That was incredibly helpful, thank you. Gives me a lot to think about and chase.
It makes sense that the center valve block would be allowing air back into the compressor, given that I'm getting a rush of air from the valve block through the disconnected supply hose.
Before things really went sideways, when I was able to raise but not lower easily, there was no sign of leaking from the bags. There currently is no bubbling at the hose fittings on any of the bags when the system is trying to pressurize, and no audible loss of air (with engine off).
The truck is currently sitting as low as physically possible; can not raise, and therefore can not lower.
Seeing as the center valve block is easy to access, I'll start there. I wonder if I unknowingly damaged something when servicing it, but there isn't too much to damage in there...
My Autel is not a bidirectional model. That would make this too easy.
Will report back.

 

Yeah, you will get a rush of air. You are also getting air out of the compressor when you pull the line but it is SO much less by comparison. Double check all your line fittings. Also know this, your front and rear valve blocks are not interchangeable. Some sellers sell them as for front or rear, this is not true. But based on your issues, I dont think this could be an issue...

I have attached a workshop file that gives some details on system operation but also, poorly, shows valve block line configurations.

 

Sweet, that is very helpful.
Are you saying that I should get the rush of air under normal/correct operation? I get the air rush while the compressor is running, and it right when the compressor shuts off.
I can feel that I'm getting air out of the compressor, but not hear it.
I serviced the valves one at a time, so the shouldn't be backward.
Would dumping any air from the reservoir tank via the 24mm plug and then running with the supply hose disconnected from the compressor serve any diagnostic purpose?

 

Yeah. Pretty sure every time I pull one of the lines off the drier there was some residual gallery pressure. Not crazy like 100psi remaining, but some. I dont think it really bleeds out 100% unless the truck has been sitting a long time. It just bleeds enough that the compressor can fire up and not fight high pressure - hence that fart thing it does time to time.

 

I don't have a way of measuring the burst of air I get, but it is a lot more than bleeding out of the system. Also, it happens when the compressor comes on and the hose is already disconnected from the compressor.

 

Yes because when the compressor runs it generally wants to fill a strut or two in order to raise the truck. So a valve block is opening and since the line is not hooked up, you are in fact dumping more air out of whatever strut or struts it is trying to inflate.

 

I'm struggling to understand the airflow path of this system, specifically if the air supply unit line is pulled from the dryer can. How is the compressor supplying the system if that line is disconnected?

 

*double post*