Hi folks,

Have spent a good few hours perusing the forms for air suspension issues, and haven't quite found a match for mine. Curious if anyone had any thoughts as to where to look next with this issue?

For context - 2006 XJ LWB, so only one front sensor - was sitting low one day after sitting for a good while. Not unusual, but it didn't raise appreciably after a good half-hour drive despite the compressor being audible a few times. Much faffing about with SDD revealed a C1889 code, which initially turned out to be the left front height sensor flapping about because the casing had actually cracked around one of the screw holes (!). On replacing the sensor - and on further inspection - the ground wire at the sensor connector was damaged so that's been replaced too.

Now, the actual problem is - the front of the car rises majestically to somewhere near its max height and just kinda sits there. An SDD 'calibrate suspension' failed after the second measurement loop, and the 'deflate front axle' task completes each time - but lowered the front end about 20mm the first time, about 5mm the second time, and subsequent runs didn't go any lower.

I've measured the output voltage from the front sensor at the sensor itself and at the ASU, and it ranges from about 1.5v (practically on the stops) to 4v or so (massively high), with no obvious jumps in between. I know every car is slightly different in this regard, but this seems pretty normal to me.

So, my question is.. how exactly does the air suspension "deflate"? Is there an exhaust valve somewhere, on the compressor perhaps? Do the corners evacuate to the tank, which in turn evacuates "outside"? I've tried 'vent reservoir' in SDD, but this makes a couple of noises from somewhere under the front end but there's no obvious air escape.

I had found a few forum threads about sticky exhaust valves, but they all seemed pretty inconclusive. Is this actually a real thing that folks have experiencing, or is this just masking something else - and does this sound like a dicky valve block in any way?

Thanks for reading this far.. comments very much appreciated!

 

The only outlet for air is a vent solenoid in the compressor. That solenoid must be commanded to open, and the valve between the reservoir and the high strut and the valve between the reservoir and the compressor are also commanded to open, allowing air to flow out to atmosphere. Any of those valves could be rusted and either partly or fully inoperative if water has been in the system for any appreciable amount of time. The important piece is that the vent solenoid in the compressor is the ONLY outlet for air to be allowed out of the system.

 

Ah - I see that one in the circuit diagram now; it looks like it's part of the compressor.

Now I'm wondering if there's a specific order - and if the struts vent via the reservoir which then in turn vents, or simply straight out via the compressor? The behaviour I see implies they're venting to the reservoir, but then the reservoir isn't venting via the exhaust valve. Only one way to test I suppose.

No problems with the air suspension prior to this, but it seems that system is really, really good at covering up little issues until it turns into a big one!

 

My issue with the system is that there is no way to remove water that gets into the system, and the dryer is not a separately serviceable part, being integral inside the compressor. Without a periodic disassembly of the compressor to get new desiccant beads in there, you WILL get water in he air system lines, into the reservoir, and into the struts, an valves will corrode. I gave up on mine when I took the compressor out and the dryer section was literally a water tank, and the vent solenoid was rusted solid. If it's storing water in the "dryer," it's pumping it throughout the system.

 

Thank you! I wish I had read this golden bit of advice several years ago!

I went thru drying the desiccant beads, bead blasting the rusty parts plus the good ole Bagpipingandy's re-ring kit for the compressor. Untold number of SDD hours with a reoccurring nightmare about "plausibility errors"! Still problem after problem including the classic leaking "olives". Car was always sitting funny the next morning.

I finally went to the spring suspension and was done with it for good!
2006 XJ
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That was my attitude. "This simply isn't worth the effort and cost to put right, considering the actual value of the car, and even if it did get put right, it will be a continuing maintenance headache needing to be repeated at some point not too far off in the future."

 

Just wanted to come back with a quick update to this.

After taking the exhaust solenoid valve cover off and discovering it resembled a big blob of rust, I removed the compressor and checked the rest of it out. The big spring was a similarly big blob of rust, and the desiccant container appeared to be filled with nasty green water with ***** floating in it. The filter, of course, was blocked solid. I am absolutely amazed it wasn't throwing any compressor or solenoid fault codes, but it did sound fine and it would (somehow) inflate the car.

...so it's now got a shiny new compressor in it, and it'll pass an SDD suspension calibration in about 15 minutes total.

However...

It still won't deflate on the 'deflate front' task, but 'deflate rear' works just fine now (it didn't before) - so I know I can exhaust from the system in some controlled way. With an ear stuck under the boot floor, I can tell the following:

1) When 'deflate rear axle' is run, there's a click from the valve block, the sound of rushing air from the front of the car, and the rear deflates.
2) When 'deflate front axle' is run, there's three rapid double-clicks from the valve block, and nothing else happens.

Obviously I'm now concerned that my valve block (and who knows what else) is full of nastiness from the decomposing compressor. Does anyone know what the 'three clicks' from the valve block signifies - does the ASU retry each operation three times, perchance? Next step, read up on "how to test the valve block!"

Also obviously, those coil conversions look pretty attractive.. but I really really want to understand what's going wrong.

 

Unscrew the valves of each airstrut to let most of air out . Start car let it rise ,drive .
do that a couple of times . You will get wet hands

 

I did try that over the weekend, and yes - got quite a lot of "wet air" out of the front ones. However, it rose majestically back to about 3" above normal height within about a minute of starting her up. I mean, it always rises to the exact same place now.. so it's doing *something* right. Honestly, all that I'm left with now is "something's up with the valve block"!

 

Or your front ride height sensor is giving incorrect information back to the system?

 

Guys I bought new height sensor 80€ front a piece.
160€ piece for the rear because of the longer stick was a bit too much.
so I bought another couple of front ones and switched the longer sticks to those.
10-15% improvement compared to before normal comfort ride.
had the two on the right side shot during winter so replaced them first with secondhand ones. Super stiff, super high 460mm on the rear airstrut gone . Only a month ago when I asked for the price of new ones did I just order.
2003 xj8 360t km.

 

Like I said earlier, there is NO WAY to get the water out of the system once it's in there. You get a wet spray opening the air lines like you did, but there's still water in there. The fact that the front rises means the valve works. There's not a separate valve for raise or lower, it's just the one valve for each strut; it's the air flow that controls whether it goes up or down.

The compressor feeds a common line in the valve body, and solenoids controlled by the Air Suspension Module can be commanded to open valves, one to each strut and on to the reservoir. The final solenoid is the vent solenoid in the compressor.

BTW, my description in post #2 above is incorrect. For some reason I was describing it as if the reservoir were between the compressor and the struts, and it's not.

So to pressurize the system, the solenoid to the reservoir opens and the compressor runs. To raise a strut, the solenoid to the reservoir is open and the solenoid to that strut. The reservoir supplies that pressure, not the compressor. (The compressor only runs if the reservoir pressure drops below a threshold.) To lower s strut, the solenoid to the reservoir remains closed, and the solenoid to the strut is opened along with the vent solenoid in the compressor, allowing air in the strut to escape.

The fact that the front raises, but too far, sounds like a bad height sensor. Both front struts share a single height sensor. The valves to the fronts open correctly, or they would not inflate. The fact that they do not deflate sounds to be like the height sensor is reporting a low height rather than the actual height. I see h2o2steam's post asking about the front sensor reading, and I'm curious about that, too. It feels like the height sensor is lying to the system.

 

Ah this is all great stuff - thanks, guys. For what it's worth, I did have problems with the front height sensor - as per my original post in this thread. I also put the voltage range I see for the front sensor at the ASU connector in the same post. What I wasn't able to really establish is what those readings *should* be - a range of 0.5-4.5v seems to be acceptable in general, but that's just based on reading other forum posts. The rear sensor readings don't seem to vary as much (maybe 0.8-3.5v); with everything manually at the "correct height", the front sensor reads just under 3v and the rear ones read about 1.5v.

Surely the actual voltage at a specific height isn't all that relevant provided it's "sane", as that's what the calibration routine is for? In other words, no two height sensor setups are quite the same?

I do still have a spare (aftermarket) front sensor that I could put back on.

Also curious if it's possible to manually actuate the individual valves. I swear I saw a screen in SDD many years ago that let you do exactly that - it had a crude diagram of the car showing the various voltages across the suspension system, and allowed you to open/close valves, run the compressor on/off cycle, and so on. Alternatively, I'm assuming each valve just wants 12v on the relevant pin of the connector to actuate!

 

Listen to wfooshee's! I had the same long repair path on a 2008 XJ I worked on for several weeks. I just did not realize that the desiccant beads are not enough to handle the water the system generates. I also live in a hot and humid place which makes it worse. Everything I opened was wet and dripping if not rusted all up!
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