Please forgive me if I violate some forum etiquette I'm new to the Jaguar Forums. Last week I purchased a 2004 Jaguar XJ8 with 117k miles from a local dealer who bought it at auction. They were unaware that it had a serious problem with the suspension and of course shortly after buying it, the suspension faulted out and the car collapsed on all four wheels on their lot! Needless to say I got the car for a tiny fraction of what it is worth.

I'm posting my diagnostic process in hopes that I might be able to help someone who has stumbled into one of these cars but has no idea how to service it. While I have a lot of experience working on domestic cars, I have zero experience working on Jaguars.

So far I have been able to use my scantool software to clear the suspension codes and get the car to try and level itself. As it sits (the way it arrived from the dealer) it attempts to elevate the rear axle first after codes are cleared. The pump comes on and runs but I hear a hissing sound coming from driver's side rear shock area and nothing happens. Eventually the car shuts down the pump and throws a fault.

I decided to do the same test but this time I placed a floor jack under the suspect corner. As the air pump ran I jacked the driver side rear corner up to simulate a successful lift. Sure enough I was able to fool the computer and this time the fault did not trip! The computer then activated the pump again and brought the front axle up.

Unfortunately my Autoenginuity software doesn't seem to allow for manual override of the system. I can't force the pump to come on and I can't manually actuate the valve block.

Essentially my task now is to verify that the leak is indeed coming from some part of the shock assembly that is replaced with the shock unit. Once I know that for sure I'll order both rear shocks for it. I'd also like to conduct a test in which I cap off the air line feeding the bad shock and let the system successfully bring up the remaining three corners without my intervention. Finally I plan to build a test rig and actually do a leak down test on all corners to properly assess the condition of each unit.

 

You can replace air shocks singly if the shock part isn't leaking. If it were me I'd look for a used one on eBay, there are plenty around. No need to whack out big money on a car that won't have cost you much in the first place. There are, of course, the Arnott rebuilds too, so consider one of these. The rebuild only puts in a new spring diaphragm, the shock part is not touched except checking for oil leaks. Being Bilsteins the shocks are very long lasting.

 

Andrew,

Welcome to the forum, and congratulations on the new purchase.

At the top of the forum is a 'sticky' link where you can download the Factory Workshop manuals, which you will find invaluable.

The air suspension system, once you get familiar with it, is easier to work on than you might imagine, and the company Arnott makes reasonably priced replacement parts.

Go to the 'HOW TO' quick links also at the top of the forum, there are several air suspension links you should read before you do anything that will save you some time and frustration.

If only one shock is leaking, it will make the car sink as the system seeks to keep the load equal on all wheels. If you find one of your shocks leaking, it isn't an absolute necessity to replace them all or in pairs if cost is an issue.

 

Hi Andrew.

Welcome to the Jaguar Forums!

As Fraser and Mac have already mentioned, X350 air suspension problems are well known, and there is a mountain of information already available in this forum if you use the Search function at the top of this page. Google searches will often refer back to this forum and may find additional threads and posts.

You can test for leaks at the air fittings by spritzing soapy water on them with a spray bottle. Bubbles indicate a leak. Test the air hose fittings on top of each air spring/shock absorber, and all the fittings on the valve block and air reservoir in the trunk under the spare tire. Dry all the soapy water off after each test.

If you find a leak at an air hose fitting, it may just need a new O-ring or you may need to trim 1/2 inch of hose with a good square cut, removing the old brass compression ring or "olive." Fit a new olive, snug the brass fitting back up (do not overtighten them!), and you should be good to go. Our member abonano has posted some good info about O-rings and olives.

If you don't find the air leak at one of the air hose fittings, you can listen in the wheel wells and probably find the leak by ear. Spritzing with soapy water may or may not work because the air bladders are covered by protective sleeves. Some members have found large holes in the corrugated plastic "gaiters," indicating the air bladder has violently burst.

The document at the link below contains the best description of the air suspension that I'm aware of:

http://www.mediafire.com/view/7rdkgg...on_Section.pdf


AutoEnginuity offers a Jaguar module that may give you more control of Jaguar air suspension diagnostics, but it's relatively expensive. Many of us are using a less expensive option with OBDII-to-USB Mongoose adapter cable and JLR SDD Jaguar dealer-level software. See the thread below for info:

https://www.jaguarforums.com/forum/x...dd-pro-134091/
https://www.jaguarforums.com/forum/x...on-sdd-135927/


This post will give you an idea of the capabilities of the JLR SDD system:

https://www.jaguarforums.com/forum/x...e3/#post531488


And the thread below shows how our member lcmjaguar fabricated his own air suspension pressure testers, which he loans out to forum members:

https://www.jaguarforums.com/forum/x...s-loan-126934/


Cheers,

Don

 

Thanks everyone. I do have the workshop manuals already and I have the Autoenginuity scantool with the Jaguar module. Autoenginuity is based in Mesa, AZ right down the road from where I live so I've been using that system since 2004 on my GM and Ford vehicles. When I need software updates I just go over to their office and get it taken care of on the spot. Once I get the air suspension up and running I'd like to take the Jag over to Autoenginuity and find out why it doesn't read the VIN and give me access to actuation / calibration commands on my 2004...

I'm sure I'll be able to sort out the leaky system but I have two key questions that I've yet to answer in the forum / workshop literature I've read so far.

1. How do I recalibrate the system after I replace a leaky component and has anyone successfully done this with the Autoenginuity equipment?

2. What is the thread size & spec for the brass nut that goes into the check valve at the top of the shock/strut?

Answers to those two questions would be very helpful to me. There is a local wrecking yard with a crashed 2008. I want to build a tool that will let me check the integrity of the rear air shocks as they are installed with shop air before I waste my time and money removing them from the junked car.

I'd never want to bring them up to full pressure after they are removed because there would be no load on the assembly.

In other words my plan is to go to the junk yard with an air tank / adapter and gauge and actually bring the rear shocks on the crashed car up to full pressure while they're still in the vehicle. If they hold I'll make an offer to the yard owner.

Thanks

 

A word of caution regarding that plan. When these units start to leak, they tend to do so only in very cold temps and over a rather long period of time. If you go on a nice Phoenix day even in winter, put a test gauge on for a hour or two, they may test fine, but in fact have a leak.

Alternatively, if the car has been in the yard and hasn't been started for a while, you might not need to test at all. IIRC, it gets cold enough there at night to help reveal a deteriorating unit. If it has basically just sat for weeks without the engine starting, and it has maintained the proper ride height, you might be good to go.

If you do test, make sure the owner will let you leave the test gauge on overnight and in the cold.

 

I agree but because it is a junk yard I probably won't have that luxury so I'll just need to get them on the cheap and do the best test I can muster!

So far it looks like those threads are very close to 1/8" NPT but I seriously doubt that is correct. I was expecting the threads to be metric or BSP.

Does anybody know why the shop manual is so insistent about the little check valve never being removed from the shock? When I removed the lines the check valves came off with them... took me a few to figure out that they were two separate pieces.

My car was bottomed out before that retained pressure was released and I'd assume any car with a serious air leak at the shock would lose that retained pressure anyway. What is the problem? Is it overextending a link someplace when the suspension is totally flat?

 

Check these out:

https://www.jaguarforums.com/forum/x...agnosis-42703/

https://www.jaguarforums.com/forum/g...-tester-98790/

 

Great! I'll stick with the 1/8 NPT then I suppose. Thanks for the links.

 

Just want to post an update and let everyone know I bought all of my plumbing components to build two testers. I want to bring the front axle up to pressure first and then the rear and let each sit overnight. I'll provide a full parts list but I've built up a test rig that includes a gauge and a ball valve shutoff with a quick connect for compressed air (times 2... one for each side.) I can use the ball valve to carefully regulate incoming air so I don't "shock" the shocks.

If I have three completely leak free corners and one bad one I'll probably just replace that one corner first in order to get the car on the road and assess it's condition and any other problems it might have. I need to get it through inspection and get permanent license plates on it ASAP. I see a bunch of deteriorated rubber boots on all of the various links... I can see $$$ adding up already!

Junk yard parts are a bust, they want a fortune for the used shocks... beyond ridiculous. I'll post an update with my test rig parts list, sources and specs and some results of my testing.

Thanks for all your help.

 

[QUOTE]they want a fortune for the used shocks... beyond ridiculous/QUOTE]
Like how much ?
Bear in mind even the new Bilstein units available on the internet market are over 600 UK pounds. Jaguar price is completely stupid bearing in mind they are the same unit. Arnott rebuilds are cheaper, of course. Arnott new (but non-CATS), units reasonably priced, but you need to decommission the CATS. Then there are the Arnott steel coil units, of course.

Air Spring - C2C41347 | Jaguar XJ 2003 - 2009 | Jaguar | British Parts UK

 

They want $450 a piece... I can get the Arnott rebuilds on rock auto for $350. I though the Arnott new units retained all factory functions!?

 

I just looked on the Arnott website the new units from Arnott AS2710 and AS2711 appear to retain all factory functions including CATS. They sell for about 450 a piece and the rebuilt factory units sell for about 350 a piece.

 

It is my understanding that the Arnott units do not have the valving and solenoid to switch between Hard and Soft that the OEM Bilsteins have, so don't support CATS, however things may have moved on. If they do support CATS, then one can replace them singly, but if not, they would have to be replaced in axle pairs. The trouble with the CATS is that in the absence of a voltage to the shocks they default to Hard, i.e. voltage to the solenoid switches the valve to Soft.

 

If you watch the Arnott installation video they show the mechanic plugging the CATS connector into the Arnott strut at the end of the repair sequence. If they don't have active valving then they must have a solenoid that "fools" the system into thinking the CATS system is working. One way or another there is definitely an electrical connection to the top of the new Arnott struts. I went through their literature and I can't find anything describing whether or not the struts are active or "faking" the presence of the active unit.

I wouldn't replace them singly because they are pretty different from the OE units but if I can determine whether I have sport or comfort shocks I'll buy a rebuilt OE single unit from Arnott.

I installed my test units on the front axle last night and applied 80psi to both. My gauge is behind the check valve which isn't ideal but if the shock leaks, the air behind the check valve should flow in to replenish the leaking air spring and I should see the pressure drop with time. This morning they were still holding tight at exactly 80psi. I'm going to ramp the pressure up when I get home but I just couldn't run the compressor any longer at night to fill my tank.

The rear driver's side corner should show a much different result but I want to benchmark the good shocks first.

 

I had a look on the Arnott website, and it seems their new air springs do not have Hard/Soft settings, so the electrical connection may connect into some "spoofing" equipment in the shock. Certainly something is needed as the CATS software is buried in the suspension control module, so difficult to remove.

The Arnott rebuilt Bilstein units have the variable damping, needless to say. My view is that CATS is a nuisance as it restricts you to one supplier, (Bilstein), and there aren't any real benefits in CATS as far as I can see.

 

It has definitely been confirmed by Arnotts to at least one of our members that their proprietary air spring/damper units do not have CATS functionality.

One of our members has posted photos of the device on the Arnotts units into which the electrical connector plugs, and it appears to be an inductor coil wrapped in the kind of protective webbed tape you see on solenoid coils. Its purpose must be to provide the impedance the ASM expects from the CATS solenoid (the CATS signal is PWM, at 400Hz if I recall - Cambo posted photos of the signal on a scope.

Cheers,

Don

 

Alrighty! Thanks for clearing that up. Makes sense now that I look at the shape of the top of the unit. I have a system similar to CATS on my Cadillac DTS (variable valving) and the Magnetic Ride Control on my Buick Lucerne (variable viscocity). Between the two systems I far prefer the magnetic ride control. Struts / Shocks for all three cars cost about the same but the variable viscocity units on the Buick really give it outstanding handling characteristics. I'll be really curious to see how Jag's cats system feels.

I found a 1/16" tube fitting adapter that allowed me to pressurize the rear shocks with my test device. As suspected the rear driver side shock had a massive leak. I ordered the Arnott rebuilt unit from Rock Auto Monday and it has apparently arrived on my door step today. I've already removed the old shock so with any luck maybe I'll actually get to drive this car tonight!

As promised I'll post a detailed breakdown of my test equipment for anyone who might want to replicate the setup. I was able to deliver air to both front and rear shocks via the built-in check valve. Three corners held pressure overnight while the fourth leaked faster than I could supply it! Excellent way to diagnose this suspension! I was also able to cap the offending port in the valve block and get the on-board compressor to level the remaining three corners with the help of a floor jack on the bad corner.

 

Reason the whole car goes flat is the ASM tries to keep the suspension level at all times even when the car is shut down and locked. So the car gets levelled to the height of the duff shock. Then of course, on start-up, you get the air suspension fault message.

 

I installed the Arnott shock on the left rear corner and got the car to stand up and drive. Unfortunately now I've got a code for an open circuit on the new damper and I've got a reservoir plausibility error. The frustrating thing is that the pump hardly runs and the variable damper should have been verified during the remanufacture process by Arnott. My autoenginuity software only shows me the reservoir pressure in 1 bar increments (ridiculous) so I don't know if the pump is reaching full pressure. The plausibility code doesn't make sense because it isn't attempting to run the compressor when it throws it!!! I'd love to understand why these systems have to be so ridiculously over complicated. I'm an engineer, at the very least I try to design systems that are easy to diagnose.


In order to diagnose the open circuit code I'll check the resistance of the new shock against the old shock and I'll put the old shock in the trunk and just plug in the connector. If there is a problem with the Arnott unit that diagnostic check should help to narrow it down.


With regards to the plausibility code I'm at a loss. My lines are all tight, the suspension holds pressure, when the pump runs it shuts off in less than 2 minutes... is there anything in the literature that describes what conditions must be met to set a certain code??? I can't find that in any of the workshop PDFs that I have. I'm used to a section in workshop literature that describes exactly what conditions must exist for a given code to set.


Is it possible that the pressure sensor itself is faulty?