He has helped me before and his advice is good this time as well! Pulled the fuse and after several days, ride height is still normal. This must mean it's a sensor or compressor issue and not a strut leak?

 

I wonder if it's the exhaust valve on your compressor that's leaking? Not something to take a gamble on as expensive as those compressors are, so it would be great if you can find somebody in your area with a tool that will allow you to take pressure readings. Then, perhaps you could pull fuse 23 again, but use the tool to monitor pressure over time. The pressure sensor is located on the compressor side of the reservoir valve block... meaning that if all valves are closed and in good shape (which it seems since your car didn't drop previously), then if the pressure drops over time, it must be leaking from the compressor itself.

 

Wouldn't that also require a control-valve from one of the suspension corners to be opened as well? I'm not sure if the exhaust valve is designed to hold working pressures - ie. if a control valve is leaking, it's possible that it might leak past the exhaust valve slightly anyways. As you stated though, as the system issues various corrections it might be hard to tell what/where it's actually starting though.

 

Well, he stated that he pulled the fuse and let it sit overnight with no drop. If we're assuming that there is a leak somewhere, then the fact that it didn't drop tells me that everything from the main “inlet valve” forward on the front valve block is holding air okay. Same for the rear valve block. Those areas of the system should be pressurized to around 150psi if I remember correctly. The rest of the system (reservoir, main lines, etc.) should be pressurized to around 240 psi or something like that. I don't know the exact operation, but I assume that the reservoir valve gets opened, the entire system is pressurized to 240 psi and then the reservoir valve is probably closed, after which the compressor vents some of the residual pressure in order to facilitate starting the next time it's needed. Either way, from the manual, the exhaust valve is designed to handle high pressures and is supposed to prevent overpressure of the system by automatically opening at "333.5 to 370 psi”.

I believe the only way for air to escape in that closed part of the system (between front and rear valve blocks) would be through the compressor (exhaust valve or bad o-rings around some of the pipes) or through an air line leak (again, more likely bad o-ring seals somewhere as opposed to an actual leak in the pipe). I guess a bad o-ring (voss connector) in the reservoir block would result in the same thing... don't know how you'd narrow it down to reservoir block or compressor.

 

I see what you're saying, but I'm just not sure the test can be taken as totally meaningful yet. The fuse just prevents the system from correcting, the leak (wherever it is) should have still been present. For it to not have leaked that day just means (IMHO) that it wasn't going to leak anyways that day.

From my experiences sometimes they just don't leak (well, OP even said this happened many nights) especially when it's warmer (or not "cold" at least) - hell when it's hot, sometimes they increase press when sitting w/ expansion and need to dump air lol. I just don't think it means much - the leak is there, I'd just re-try when colder.

I only mentioned valve block because usually after shock replacement, the valve block is the #1 fix of leaks - I don't know if I'd throw parts at it either though, I'd rather know what's really happening - that's just what the indy guys tend to do.

I don't THINK the system maintains pressure between block/compressor? Personally it just sounds like it dumps all of the air. FWIW when I did my software update at indy it STILL doesn't do the purge like my RRS did, but I think his software versions were out of date (I know TCM was because it told me my current ver. was newer, so I'd assume same goes for rest).

I don't know what benefit you'd get from keeping partial pressure other than reducing the likelihood of leaks internally (from one side of a solenoid to other side of solenoid, not to atmosphere).

I think suspension pressure is much lower than you stated, but again I could be wrong. I put digital pressure gauges in my DII and typically it's 65ish but never more than 85 even when I was towing a 20' boat with stuff in the back.

Anyways at the end of the day, I don't know how it can be the exhaust valve simply because air has to get TO the exhaust valve - for it to get there, another valve or valves must have failed. If your explanation of the system is correct - it would still empty the link from suspension valve blocks TO the exhaust valve. I guess you're thinking once that pressure drops too low, the suspension valve blocks aren't designed to handle the pressure differential with nothing on the other side of the valves?

I'm still leaning more towards the main gallery / suspension valve blocks because it got worse when towing, and the only parts that see any increased pressure during towing or heavier loads are those first initial control valves for the suspension corners. Or like you said, some o-ring or leak on that same side of the system.


I'm gonna do some digging.

Disco SLS diagrams are super easy to find - not so much with the new stuff!

 

So, there is another possibility -- As I understand it, the desiccant (air drying beads) get old, and start to break apart. As I understand it, some of those little crumbs can get into the system and start causing grief... sticking a valve not completely closed, etc.

Have you done a rebuild of the air dryer portion of the compressor? It's something on my list to do this spring on mine, and I have found on 2 occasions where it was simply down to the bumpstops after 2 days -- and it doesn't leak a drop of air for a week at a time, generally.

Justin @ Lucky8 did a video about this:

Just food for thought,

Dave