X350 Hard Suspension

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gmiller
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X350 Hard Suspension

Postby gmiller » Wed Oct 11, 2017 7:55 pm

Hi,this is my first post here, so I hope I get it right.

I have an x350 2.7 2005 diesel which I bought about 6 months ago with 125,000 miles. It has developed an issue where the ride can sometimes be quite smooth and other times it is very hard / harsh, to the point where it is uncomfortable to drive due to the vibration / feedback from the road. For example, I drove for around 40mins yesterday and the ride was smooth. I then stopped at the garage to get some fuel, and when I started my journey again the suspension was quite hard.

The issue of hard suspension does seem to coincide with turning the car off for a short period of time, then starting up again. If I leave the car for a couple of days the suspension is usually smooth to begin with, but will soon get hard again if I do a quick stop / start.

Ride height is normal, there are no dashboard error messages, there are no DTCs. Any advice would be much appreciated. Thanks in advance.
George M

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Re: X350 Hard Suspension

Postby J44EAG » Wed Oct 11, 2017 9:31 pm

Welcome to the Forum.

Valve block issues near the air tank in the boot can cause problems. Cheap enough if bought second hand from Eurojag or similar breaker.

Rob Jenner has some knowledge of similar issues. He may be able to offer some guidance.

Have you done any work on the compressor or air dryer unit? The media in the dryer can get quite wet and soggy. See my article about six months ago in the magazine which gives some idea of what is inside the compressor unit. Almost certainly changing the media will do no harm at all.

The absence of fault codes is annoying and frustrating for diagnosis. One might be tempted to investigate the CATS system as hard/soft is controlled by a separate module.

Others here might be able to offer further help. Keep watching your post here for any of their comments over the next few days.

Mike K
X350 Co-ordinator

2004 XJR

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gmiller
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Re: X350 Hard Suspension

Postby gmiller » Thu Oct 12, 2017 7:01 am

Hi Mike,

I have not looked at the compressor or dryer yet, but I have read your article, and will certainly get round to performing maintenance on this soon.

Thanks also for the pointers to valve block and CATS, this gives me something to start with.
George M

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Re: X350 Hard Suspension

Postby gmiller » Mon Dec 04, 2017 8:17 pm

Have been doing more investigation into hard suspension, and decided to use IDS datalogger signal detection to check out all of the electrical inputs regarding the suspension module. The theory being that if one of the sensors like an accelerometer was feeding bad information to the computer, then this make keep the suspension in hard mode.

All inputs seem to be working as expected and within specified parameters. I was specifically interested in the switching of hard to soft, as when stationary the suspension is supposed to switch into hard. IDS was reporting that all 4 suspension units were switching when I moved off from stationary, however there is no indication of the voltage being supplied to each strut.

Could it be possible that the suspension computer is switching suspension to soft, but the required voltage to achieve soft is not being applied?
How would you test for voltage at each strut considering the car needs to be moving (and I don't have a rolling road)?

I am planning to take a look at the suspension computer at the weekend (behind the rear seat I understand), and will be looking closely at the grounding point which is supposedly there. I have read in other posts that some members like to use the Duralac product to inhibit corrosion on bolts and screws, but is this something you would use on an electrical grounding point to inhibit corrosion?

Any and all advice and comments received gratefully.

George.
George M

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Re: X350 Hard Suspension

Postby J44EAG » Mon Dec 04, 2017 9:43 pm

Definitely no Duralac on electrical ground or plug points George. It is an ISOLATION paste which will not pass current. It is designed to prevent galvanic issues between two dissimilar metals. Best advice is to clean up ground points if corrosion is present, just rub a trace of light oil on the ground point and ring terminal, then you can smear the outside of the joint connection with some electrolytic grease on the outside of the job once completed to prevent external corrosion. Again, that sort of substance can act as an isolator similar but not as good as Duralac. Duralac paste is messy stuff and is toxic. Rubber gloves when dealing with it. Best used within a bolted joint or when using rivets. Clean of all external exposed excess. Its not nice material to naked skin or the human body generally.

As regards the suspension issues, dealer level IDS or other suitable diagnostic gear is the way to check what may or may not be happening voltage wise. I can`t think of any other way to check the issue. Regret my own experience hasn`t yet had to deal with or fathom hard suspension issues. I think you are going in the right direction though as regards module investigation. Worth perhaps a good Google and see what others experiencing a similar issue might offer as advice.

Sorry, my knowledge has run out on this issue. Keep at it.

Mike
X350 Co-ordinator

2004 XJR

cornershop

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Re: X350 Hard Suspension

Postby cornershop » Fri Jun 28, 2019 7:36 am

Hi,this is my first post here, so I hope I get it right.

I have an x350 2.7 2005 diesel which I bought about 6 months ago with 125,000 miles. It has developed an issue where the ride can sometimes be quite smooth and other times it is very hard / harsh, to the point where it is uncomfortable to drive due to the vibration / feedback from the road. For example, I drove for around 40mins yesterday and the ride was smooth. I then stopped at the garage to get some fuel, and when I started my journey again the suspension was quite hard.

The issue of hard suspension does seem to coincide with turning the car off for a short period of time, then starting up again. If I leave the car for a couple of days the suspension is usually smooth to begin with, but will soon get hard again if I do a quick stop / start.

Ride height is normal, there are no dashboard error messages, there are no DTCs. Any advice would be much appreciated. Thanks in advance.
This sounds quite similar to the issue I’m experiencing - did you find a resolution?


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