Hi all, looking for a little help to see if I'm going in the right direction or not. I have a 2006 jaguar XJ X350 4.2 N/A LWB that I've owned for around 18 months, it has 109000 miles and has received very little in terms or maintenance, so I'm ploughing through a whole list of things gradually. I think maybe my air damper/shock units are possibly worn out and need replacing, but I'd be interested to know the thoughts of others who have vastly more knowledge of the air suspension system than I have. I've never owned an air suspension system car before and have little knowledge about it.

Ok my issue is going over what would normally be considered small pot holes or small ruts in the road for a regular type suspension system car and hardly felt, my car you feel these ruts holes bumps in the road very hard, also when going over a speed bump near me I have to literally slow down and roll over it at less than 5mph, literally roll over it slowly, any faster and as the front wheels come off the speed bump onto the road the chassis slams down onto the top of the speed hump, where as my wifes corsa can go over it much faster.

Does the above point to my air shocks/dampers having failed the oil part inside or whatever it is that damp the bumps, sorry for my lack of knowledge on the dampers, additionally the car air system keeps all 4 corners inflated to the same height, and in the morning the car is not low on any corner etc so the air system itself seems good thats why I'm suspecting the air damper itself for its possibly lack of sufficient damping capability over bumps.

I hope all this makes sense to someone and I appreciate your thoughts and knowledge in advance.

 

Hi Mark,

I have moved your post to start your own thread since your issues differ from those in the thread to which you originally posted.

I have also added some line breaks in your text to make it easier for others to read without going cross-eyed.

It is possible that even though your air springs are still holding air, the shock absorbers/dampers are failing. Other very common issues are the lower shock absorber bushings, stabilizer bar links, and control arm bushings. A good independent mechanic may be able to diagnose the issue(s) upon inspection.

Cheers,

Don

 

Many thanks for this and the advice Don, only yesterday I brought two new front upper wishbones as one of the ball joint rubbers has split (havent fitted them.yet), and have only just replaced all the rear upper and lower control arms, rear track rods and rear ARB links, and rear wheel bearings. Could potentially be renewing the front end suspension also then.

 

A fault detected in the suspension system and sometimes other things related to on-road performance can cause the air suspension dampers to go into "Hard" mode. Normally they go to Soft pretty soon after moving off in the car. So the first thing to do is check for stored codes, Not all are cleared when repairs are done.

So, have you had any work done at all recently ?

 

Hi Fraser,
No work done on the car other than replacing the rear upper and lower control arms, rear track rods, rear ARB drop links, and rear wheel bearings, due to a couple of worn bushings at rear, so decided to change everything at rear end whilst I was there.

That said the suspension exhibited the same symptoms before i did that work on the rear, and i have no stored codes for the air suspension, this was why i was thinking maybe the damper/shock absorber part is worn and the air spring part is good??

 

The solenoid valve at the top of the struts needs a 5 volt supply otherwise it defaults to hard.

This supply comes directly from the air suspension module.

Try a hard reset of the whole vehicle.

Ensure all air suspension error codes are removed.

Lots of info here:
https://www.jaguarforums.com/forum/x...w-reset-82847/

 

Hi Meirion1
Please excuse my lack of understanding in some areas, when you say do a hard reset, do you mean just to disconnect the battery and then reconnect after a period of time? If so I have done this for working on a few other things and the suspension has remained unchanged in its damping characteristics.

Its been like this for the last 18months that I've owned the car, but ive had a fair few things to get through fixing on the car, but now I'm working on the suspension, as it needs to ride and handle as it did originally when new.

 

Don't worry my understanding is limited too.

The answer may be in removing codes-take it to an independent jag mech if you

have no scanner or a jag dealer as a last resort.

Are you in the UK?

 

I'm in the UK,I have a code reader that can also clear codes as well, I have no air suspension fault codes though

 

Hi Mark,

Most code scanners can only read the generic OBDII Powertrain codes (P- prefix). The diagnostic trouble codes (DTCs) related to the suspension are Chassis (C-prefix), Body (B-prefix) and Network (U-prefix) codes, and can usually only be read by either dealer-level diagnostic systems or high-end third-party tools like those from Autel, Launch, Snap On, etc., or computer-based systems like AutoLogic or AutoEnginuity with the Jaguar expansion module. In other words, the scanners most DIYers own simply cannot read the suspension-related codes.

The voltage to the ECATS solenoids at the top of each air spring/damper unit that meirion1 mentioned has an amplitude of 5 volts, but it is pulse-width modulated (PWM) at 400 Hertz. so it can only be accurately measured with an oscilloscope. However, you may be able to read a small AC voltage at the connector, but only when the car is moving, since the default state of the dampers is firm when the car is in Park.

If you can find a forum member or independent shop with the Jaguar dealer-level System Driven Diagnostics (SDD), many aspects of the air suspension can be monitored and even re-programmed.

There's a lot of info about the system and its operation here:

Air Suspension & ECATS System Summary: Components & Operation

However, I still recommend having the suspension inspected for worn parts, especially those I mentioned earlier.

Cheers,

Don

 

Thanks for the info and advice Don, I only have an icarsoft scanner but my independent jag mechanic has full diagnostic facilities and all software updates, so when it goes into him for the transmission fluid change may well be worth him running a scan

 

Keep in mind the front upper wishbones can only be changed with the struts removed. So if you feel you are having strut related issues after digging into it further you can plan the jobs out without going backwards.

 

Hi Mark,

I am interested to see where this goes. I have a 2004 XJR which definitely "thumps" loudly in the rear over potholes in the road. Very annoying in an otherwise quiet car. My passengers have noticed and asked what is wrong, so it's not just me. The car has 70,000 miles. I have personally replaced rear upper and lower control arms, tie rods, and arb links. The rear airshocks appear to be original. I also get the thump under hard acceleration from a stop.

It appears the front end received all new control arms and airshocks prior to me. The shocks appear to be the oem bilstein sport model. But still something does not seem right up front too. As if there is a worn ball joint, like a shift over certain surfaces. All new Michelin Pilot Sports has made it better, but not "perfect" The tire guys did align and say everything is tight. Which seems correct, there are no noises.

I do get occasional Air Suspension Errors on the display. And then they go away. Maybe the car is staying in Hard even when the error is not displayed? Or maybe the rear shocks are just worn out.

I have the JLR Mongoose and IDS software to read the codes, but that has been finicky with my car. I think as mine is an early US model perhaps. I have to use the earlier IDS 125, not the later SDD 138. That is a whole other project...

 

FWIW I too, noticed this thumping from the rear on my first X350, a 2003 car, yet not on the next one, a 2007. I do remember remarkiing on it at the independent shop that used to service the 2003, and was told it was a characteristic !! My view on the air suspension system is that I am very glad to see the back of it with my purchase of an XE !!

 

It seems that you have done a lot of work on the back end suspension and once you have confirmed that

it is not a joint or bush then that leaves the strut itself.

I am sure you are aware that the strut is a combined hydraulic shock and air bellows.

The bellows can leak, sometimes catastrophically, and the shock can also fail noisily.

AFIK there is no way to confirm that the shock has failed except to replace it (or both sides).

You will have error codes stored and you could delete them all and see if that makes a difference

but from my reading of this forum when the 5 volts to the struts is absent the ride is really hard all the time.

I am guessing that the thump on hard acceleration could be a strut or the prop shaft.

 

I don't drive this car a lot, but certainly, it holds it's height over time, so I don't think its a problem with the bellows. However meirion1 makes a good point - perhaps it is the hydraulic portion of the shock that has begun it's demise. I think I can buy into that. I certainly planned on replacing the rear shocks at some point, so why not now! But first let me see about the 5 volts.

Th acceleration thump does not seem like the prop shaft. There is no noise going from accel to deccel, I am thinking it is more than likely the strut. I just hope Fraser's mechanic is wrong, that its not a characteristic of these otherwise wonderful cars.

 

Hi Gary,

I work on a lot of X350s and can say without question that a thump in the rear suspension is not a common characteristic of an X350 that is functioning properly.

My first question would be, are your spare wheel and battery properly secured? A lot of X350s I see are missing either the spare wheel securing hardware, the battery securing bracket, or both.

The shock absorber lower bushings deteriorate, so those would merit inspection.

Some of the bushings and ball joints in aftermarket control arms have proven to deteriorate prematurely.

The electric signal to the ECATS adaptive damping solenoid valves at the tops of the shock absorbers has an amplitude of 5 volts, but it is a 400Hz square wave, so you will not measure 5 volts DC, though you may be able to measure a smaller AC voltage depending on your meter's capabilities. But remember that when the car is in Park and at rest, the default state of the suspension is Firm, so you may not see the signal at all unless the vehicle is moving. If you don't have the CATS FAULT warning on your instrument cluster, the Air Suspension Control Module thinks the system is operating properly. But it would be worth using your IDS/SDD to scan for codes just to help rule out an ECATS malfunction.

A basic test of the shock absorbers can be done by the traditional "bounce & jounce" manner, by pressing down repeatedly on a corner and then allowing the car to settle, counting the number of rebounds. More than 1.5 or 2 bounces after you stop pushing suggests the shock absorber is failing. Just remember that the body of your X350 is aluminum, and don't be too physical when doing this test.

It's unlikely that you would get a thump from the rear due to a failing wheel bearing unless you were also hearing a howling or roaring sound.

What about the CV joints in your axles? Any cracked or leaking boots or unusual free play between an axle and joint?

Cheers,

Don

 

Hi Don,

Wow - a lot of great info! First I am glad to hear that this is not some unpleasant characteristic - so - I will get to the bottom of this!

Yes - all the tire and battery hardware is in place and tight. And CV joints appear tight and intact. There is no clunk when modulating the throttle to suggest any play in the drivetrain. The shock bushings are not perfect, but I didn't detect any play when replacing the lower arms. I purchased spares, but concluded that i'll replace the shocks anyway at some point. I guess i have not looked at the top bushing (bearing?). The bounce test is very firm, with no additional rebounding. No other noise, so I assume wheel bearings to be good. All the parts I used are Lemforder oem and perfectly matched the original castings. I did the work at about 65K, now have 72K

So I guess my next steps are to try to get the IDS running. It has connected in the past, but I have not spent much time with it. I was never able to get the SDD to understand my VIN for some reason, so it sort of just stops there. I wonder if it's because mine is a very early X350. The VIN plate shows manufactured date of 02/03. Carfax says 12/01/2002. BTW - perhaps another clue - the main reason I purchased this setup is the car sits a little high. Maybe 15mm in front and 10-12mm in the rear. So the plan is to correct the height. Best laid plans of mice and men... I will also check the 400Hz 5V signal with my oscilloscope when I figure out how to get at it.

Here is another weird clue - I have has 2 Michelin Pilot Sport tires develop bulges in the sidewall. Both right rear (where the thumps seems to come from). This recent tire has maybe 200 miles on it. Ouch. I declined the road hazard warranty. Hard setting on just that shock perhaps?

 

I can tell you that if the hydraulics in the strut (rebound) are bad or failing that it can make one heck of a noise. I recently had a failed front strut and decided to just change both fronts with a pair of rebuilt units. They have only lasted four months and one is bad again but that is another story but part of this insight. What I had happen is that upon changing the two struts with the rebuilds I immediately developed one heck of a thumping noise in the front of the car that sounds violent from the driver seat. It never had been there until I changed the struts. I had also installed new upper "A" arms when I put the struts in. I am a pretty fair wrench but I thought that maybe I had installed the arms incorrectly and went through all of it again reinspecting all the bushings etc... to no avail. Long story long I finally could slightly hear the newly installed right front strut making noise just with me bouncing the car. Imagine the weight of the car rebounding against a failed shock. Bear in mind the struts were holding air just fine so the car was able to be driven but it scared the living daylights out of the Mrs one day when we hit a bump and the car sounded like it was coming apart. I would be willing to bet the noise you are hearing is a strut that is failed hydraulically or is on its way out. As for my situation, the rebuilds have started losing air and with the one making the bad noises, I have made the decision to convert the entire car to coil-over. So my beautiful XJR sits in the driveway waiting for my fun money account to afford the purchase. If your desire is to keep the air system, I for one would say that new Bilsteins are the way to go. I thought I was saving money but if you count the time and effort I have put in over the past 6 months removing and installing rebuilds, plus lost time that I couldn't and now can't drive the car, it would have more than paid for the Bilsteins.

 

A couple of ideas for helping your IDS/SDD:

Whenever you use IDS/SDD, connect a battery charger and confirm that the battery symbol in the upper right corner of your computer screen is green (actually, I can't remember if IDS has a battery state of charge indicator, but SDD does).

Be sure that, if necessary, you go to the USB menu and attach your VCI (Mongoose, Ford VCM, Davina, etc.). If your VCI is not attached, IDS/SDD cannot communicate with your vehicle.

Enter the VIN manually instead of selecting "READ." This may help IDS/SDD pull up the VID block data from its own database instead of trying to retrieve it from your car. It is possible that your car's VID doesn't conform to the expectations of IDS/SDD and entering the VIN manually may help you get past that screen and on to the diagnostic and service options.

Cheers,

Don