Hi guys,
just adding another Air suspension thread, i already spend multiple hours going through other threads in this forum, i already spend a good amount of time and money replacing parts but i still get Faults, but iam definetly not willing to give up the Air suspension.
Its the 2006 Jaguar xj8l, 4.2 V8.

Last year i had a badly leaking front strut, i replaced the two front struts, after that i drove about 8k miles without Air suspension fault and a good ride, then it came back and it actually turned on Damper firm sometimes. I noticed that one Rear strut was leaking back and the car dropped overnight, i replaced the rear strut. In both cases (front rear) i bought rebuild OEM struts (Green, Comfort)
But the Air suspension light came back on, it is not damper error firm, but it is not the good soft ride i experienced before.

The Error code i get is the is the famous Reservoir plausibility error. C2302
All struts seem to be leak free, the car does not drop, i took multiple exact measurements before and after the car was sitting for a while, noch change at all.
Of course the Air suspension fault disappears after sitting for a while but most of the time it comes back one quite quickly a few minutes into driving.
I used the Data stream (Carsoft I930) to track some data, basically to track the compressor status, Air pressure sensor and the the two solenoid valves.

The compressor starts as soon as i go over 25mph, it starts increasing the pressure, but sometimes it comes on put the pressure does not increase and than the air suspension light comes on. In other cases it starts increasing the Air pressure up to 12-13bar (needs about 2 minutes) then it shuts off for a while comes on again (starts at maybe 11 bar) runs again and usually then i get the Suspension fault (if i didnt get it before)
The air pressure with compressor off is usually somewhere between 6.5 bar (pretty stiff ride) to 7.5 bar (much better ride)
I also turned of the car and run the compressor manually by jumping the relay R1, i went up to about 14.4 bar (took about 2.5-3 minutes), then the exhaust manifold opened and there was a clear air hissing sound. But when i run the air compressor manually for example to 13.5 bar and than turn it off the pressure goes down 13.4, 13.3, 13.2,... within seconds.
If the compressor turns off while driving the drop is from like 13.4 bar to 2.5 bar or so, is this normal? (Reservoir solenoid from OPEN to CLOSED)
I just try to find the bad part and right now it is really a bad time to spend money on things i dont need.
So should i replace the compressor or rebuild (did this last year but would try again since its not a lot of work and not expensive), is my valve block leaking?

Just replaced front control arms and the rear tie rods and sway bar links, i want to get my nice comfort Jaguar ride back... please help!
Would be great to get some opinions and also it would be helpful to learn what Data stream numbers are appearing when everything is ok.

Jonathan

 

The pressure in the reservoir shouldn't have anything to do with that actual ride quality; it's simply a source to inflate the struts. Low pressure means the struts can't be raised, though, and you get the plausibility error because the compressor runs but the pressure doesn't come up. That's the reason your ride is better with higher reservoir pressure; it's able to air up the strut and raise it.

When you ran the compressor manually with the car off, the Air Suspension Module would be off, and there should have been no valve action. I don't think you should have been able to pressurize the reservoir, but I might be wrong. I know the module has constant power and switched power, so maybe it "knew" what you were doing and allowed the reservoir to pressurize.

6.5 or 7.5 in the reservoir is too low. If that's all you get while driving, there is a problem and something's leaking somewhere.

Also, once the plausibility error appears while you're driving, the system shuts down and makes no attempt to do anything else until the car is shut off and restarted. It won't run the compressor, it won't raise or lower strut levels, it won't do anything.

I can't help you with what anything should be other than what info is in the air suspension sticky, because it wasn't worth the money to me to replace EVERYTHING, which was how bad mine was with leaks, water in the system, compressor ick, and so on, so I put a set of Arnott coilovers on it and never looked back. I've never experienced good air suspension, so I can't compare to what should have been, but the car is vastly superior to how it was on the failed air system. you see so many people saying "Don't give up on the air system, it's fabulous when it's right!" It's just not worth doing, in my opinion, when it's a third or half of what the car's worth, and will still need redoing in the future. Air suspensions have a much more limited lifespan than steel springs.

 

the car rides better on s-type coils period end of story. it’s time to throw in the towel

unfortunately you have a 2006 so you need to buy from arnott or suncore to turn the light off

 

Iam not there yet, i think the Air suspension is actually not that bad and no difficult design (mechanically) i will build now a easy testing fixture so i can test each single component for leaks.
- Each strut by its own
- Reservoir
- Valve block
- Air compressor

That should be pretty easy with the valve block in the trunk. Does anybody know the thread sizes on the valve block in the trunk, i want to get some caps, so i can block the single Out/Input off during testing the different cycles/components.
I do now that front struts have 6mm tubing and rear has 4mm tubing.
My plan is to pressurize each line with about 12-14bar using an air compressor and than i should find where iam loosing air.

Jonathan

 

Just want to close that post...
I still believe in my air suspension and i also got it fixed, it turned out that the valve block in the trunk was the issue and was leaking bad.
I developed a good way to diagnose the complete Air suspension system and explained the whole procedure including referencing part numbers, see link below (thread #40)
https://www.jaguarforums.com/forum/x...2/#post2459923

After spending some time understanding the Air Suspension system i think it is a fairly easy system and easy to diagnose. To maintain it is also not too expensive if you dont buy at Jag dealer and do the repair yourself, obvisouley Jag dealer costs are a nightmare.
I bought Rebuild OEM struts from RMT Mastertech, that these struts fail after some time is kind of normal since the rubber wears out, even normal struts fail at some point, struts are always a part that wears, thats just the nature of struts. RMT sells rebuild OEM struts for about $240 each, thats not to bad, and rebuilding them is really not such a big deal since they basically only replace the Airbag.
Replacing struts on the Jaguar is really not difficult (except if you have to fight with a corroded strut bolt), changing other parts like air compressor or the Valve in the trunk is also super easy. RMT does has a "Lifetime" warranty but they honor their warranty only if an ASU certified mechanic signs off on the installation, i assume most people who buy these install themselves, and you dont have to be a certified mechanic to install a strut on a XJ8 since it is really easy. Maybe if you have a friend or relative with a car shop they are willing to finally "sign off" on the installation, just a thought ;-)...
Rebuilding the compressor with a $25 rebuild kit is also very easy and most of the time the necessary cure in case of air compressor failure.
Only corrosion of bolts can make all this a pain in the a**... guess how i know living in Wisconsin!?

Everybody has the right to have his Opinion, i think the air suspension is great when it works and know after spending some time and test everything with a very easy test-setup i know how to act next time when i have an issue or error. Overall i think the Air suspension in the Jaguar is actually very in-expensive to maintain and a simple design, especially with all the components easy access, compared to other vehicles.

Not meant to start any discussion i just want to help other people in the future and i hate to browse through forums and all posts just to end up with the last post were you hoped to get some kind of answer but then it stops there...

To come back to my question above:
As one member mention the pressure of the pressure sensor has actually nothing to do with the ride pressure, in my case it appeared to be different because the valve (where the sensor is located) was leaking so bad.
In general when you start the car it should start filling up the reservoir once you go over 25mph, in this status you should see the pressure building up on your i930 carsoft reader, the reservoir solenoid valve should be open while the compressor status is "ON", the compressor runs for 2 minutes and should fill up to 14.4 bar before it shuts down. Depending on how empty the tank was it may takes two cycles. In this case the compressor runs for 2 minutes, stops for i believe 45 seconds to cool down and then runs again to fill up to 14.4 bar.
When the compressor is off the reservoir solenoid is usually closed an the pressure on the sensor doesnt really matter and varies between 2-7 bar.
The above behavior is what i watched during a drive without any Air suspension faults popping up so i assume that the behavior you are looking for.
i think it is helpful to know what are the "good"-values you want to have when you have somekind of error in any system, since it can help to find the issue.

As mentioned above you see the link were i put together a extensive manual and procedure how to test the different components for leaks, including lines and all connections.

 

Replacing an air spring diaphragm is essentially the same as replacing a broken steel coil spring, it just costs more !
I had very little trouble with the air suspension on my two X350s I owned between 2010 and 2019. The first, a 2003, had to have a compressor at very low miles (35k), but the replacement was still on the car and working at 115k when I part-exed it for an X358, the restyled version.
It was the very short life of some of the suspension bushes that got me cross. This issue was never sorted out by Jaguar, and is, essentially due bad design.