I have a 2004 XJ8 with 89,000 miles that has an air suspension problem. All four shocks were replaced with ARNOTT air shocks about eight years ago. Just recently both rear shocks have been bottoming out but the front shocks stay in normal position. Sometimes they drop after just a couple hours, sometimes it take overnight and other times they stay up for several days. When I start the car the compressor runs and pumps up the shocks as normal so it appears the compressor is working OK. I’ve checked the connections at the top of each rear shock and at each of the connections to the valve block with soapy water but no bubbles. Since the front shocks are having no problem I’m thinking that the connections at the compressor and the reservoir are OK. Does anyone have any ideas as to where the problem lies?

Thanks for any and all help.

RJFS

 

Are there any warning messages on the annunciator when you (1) turn on the ignition, and (2) when you start the car ? If rear air springs are collapsed, but not the fronts, you should get a warning message. The way the suspension works is the suspension controller always tries to keep the car level, so when the engine is off and the car locked, the suspension controller wakes up at intervals to see if the car is level. The compressor will not be used, so all it can do is let air out of the springs to level the car. Yet you say only the rears are down when you come to restart the car. This indicates possibly a fault with the height transmitters by each rear wheel.
Other thing to look at is the valve block which traps air pressure in each spring and allows that pressure to be adjusted based on the height transmitters. If the valves leak slightly pressure will be lost. Of course when the engine, and hence the compressor is running, such leakage doesn't matter too much, the suspension controller will open valves to allow air from the reservoir into the springs that are losing height, , and start the compressor to pump more air into reservoir. No measurement of air spring pressure is made, the system works entirely by suspension height values sent by the height transmitters.

 

Thank you very much for your detailed reply. The message that appears when the ignition is turned on is that the vehicle is too low. That message disappears after the rear shocks have been inflated to normal height. I used a wrench to check each connection at the valve block in the trunk and they appeared to be tight. I also applied a soap solution around each to check for a leak but no bubbles appeared. You mention the height transmitters by each wheel. Couild you tell me where they are located and how I can check them? Are they something that can be readily identified as bad, and is so, can they be replaced. Perhaps only one is bad and, as you described, the auto-correction height adjustment may be causing the good one drop that side. This sounds like a real possibility.
Again, thank you very much for all your help.

 

I too have had to manage suspension problems. The good news is that they are manageable… the bad news is that your patience can be tried. I found success after my third attempt at soaping the tank manifold/block connector. I sprayed it generously and then walked away for lunch. When I came back two hours later I had bubbles like crazy! I had simply been too impatient! Good luck, Chemosabe.

 

Thank you very much for your reply. I will have more patience when checking for leaks. As I mentioned in my original post the time it took for the shocks to bottom out was anywhere from 1 hour to three days so you are correct about being patient. I will give the test more time.
Thanks again.

 

My opinion is that your problem is 8 year old shocks. That's about the life of these things regardless of how many miles. My experience with solving air suspension on several X-350 jaguars is that it's almost always the shocks. I have seen friends spend thousands of dollars replacing compressors and height sensors and checking for leaks in order to AVOID replacing the shocks. In the end...it was the shocks.

Good Luck
Jeff

 

Thanks Jeff for the information. I agree the air suspension on these Jags is a bit of a problem and very expensive. I'm wondering if replacing them with the coil spring replacement units would be best in the long run.
Thanks again.

 

The struts can leak in two ways:
You hear a bang and there is a hole in the side of a shock.

or often in cold weather there is a small leak at the top.

I have attached a photo of the top of mine:
The solenoid with the two wires has been removed.
If you poke around the inside of the outer ring you can feel it give a little
this is the hard foam seal which can contract and leak so you need to get the soapy water
in there to see a leak.
Fill that labyrinth with soapy water if nescesary

My Jag is 20 years old and on the original struts

sorry it's a bit out of focus

 

Thanks for your reply Meirion1. I live in Missouri and coincidently the weather is changing and the temps are dropping. The cold weather factor may be the culprit as you mention. I'll follow your instructions and see if I can locate a leak.
Thanks again.