Car suspension, mainly the front pair, deflate and allow the car's front end to drop within two hours... No apparent leaks on the struts. The question for the experienced is: does the air compressor have a check valve in it to prevent air from leaking past the piston when it is not running?
I have also started to notice over the last day or two, that the front end appears to rise (over the horizon) when I come to a stop at traffic lights. This is what has me asking about air leaking past the piston in the compressor...

Your thoughts please!

 

Hi Na5h,

To answer your specific questions, yes, there is a mechanical check valve in the compressor assembly to prevent air pressure from escaping back through the cylinder (see the fourth photo album below for photos of the components of the check valve). There is also an electrical exhaust valve that releases pressure as necessary (and to partially reactivate the desiccant in the dryer by backflowing dry system air through the desiccant beads).

I have to run, but if no one else has responded by later this evening I'll try to give you some thoughts.

Cheers, Don

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The front wheels are controlled as a pair, the rears individually. You could have a front height sensor problem, in fact you say the car also rises at stop lights, so it does tend to look like it. As you have no fault message, there will be no codes to look at; the system thinks it is operating normally, so I tend to think it is the front sensor sending anomalous readings. Of course I could be wrong, but don't rush into buying new front air springs just yet, not until the ride height has been recalibrated and the sensor checked out.

Can you remember if anything happened to the car just before this problem started ?

PS: there is a valve block that controls the air in each spring unit and allows air in and out. Air is also exhausted via the compressor to clear water out of the trap after a run. You'll hear a woosh like a whale surfacing that gradually dies down.

 

Thanks Don and Fraser for taking the time.
In answer to your question, Fraser, yes the drivers side front had a leak and was replaced about two months ago. The car still kept on dropping it's height while parked and I attributed that to the cold temperatures. I have been out of the country for over three weeks and now with the temps in the 80s I started looking into it again.
Couple of additional questions:
i) where is the front height sensor located? Perhaps I could look at it over the weekend.
ii) what would I look for as far the sensor is concerned?

As info, yesterday afternoon, after the car had been parked for about 1 hour, as I was walking back up my driveway toward the car parked further up, I noticed that the drivers side appeared to be lower than the right side of the cars front end. I did a quick and dirty 'how-many'fingers' measurement from the top of the tire to the edge of the wheel arch and confirmed that the left was lower than the right. Thoughts..?

 

To add my $0.02 here.

Check the air line going into each strut with a soapy water solution. If the struts were replaced they should have come with new nuts, O-Rings and olives. If they swapped those parts out - this could be your problem.

Another issue I see over and over again is overtightening of the air line nut to the strut. The proper tightness is only 6Nm (basically finger tight + 1/4 turn of the wrench. Anything tighter will flatten out/rupture the O-Ring causing a minor leak of the stored air in the strut when the car isn't running - which is one of the symptoms you described.

The good news is these parts are available relatively cheap from Jaguar - I have a post with the part numbers. The fronts are 6mm sized and rears 4mm.

Hope this info helps - Anthony

 

Any fault message on the message panel ? Car dropping height at the front should trigger a fault, like "air suspension fault", or "car too low" if the height sensor is working. This also generates a fault code that needs reading.

 

My :

If there is still no error message, this case could be similar to
Faulty air suspension shows no error code
or
04 XJR Front End Suspension On The Ground - No Codes!

Please check Fuse 12 of the rear power distribution fuse box behind the battery.
It should have 12V+ when ignition is on.

If you suspect a suspension leak but cannot find it, please try to change the o-rings first.
They often suffer sporadic failure.

 

Thanks to all for their suggestion on what could be wrong causing the car to loose it's air out of the front struts...

The front left strut (drivers side) was replaced about five weeks ago and yesterday a soapy solution mix showed there to be an air leak from the top mounting area. So, another strut in a day or two...

 

Hi Na5h,

I would doubt that you need a new strut.

Leaks from the O-rings on the brass fittings on top of the shocks are very common, and abonano has reported that a common cause of leaks is over-tightening of the nuts on the fittings, which should only be tightened 1/4 turn past hand tight. The compression rings, or "olives" may need to be replaced, which will require trimming the old ones off of the air line. The instructions for doing this are in the X350 Workshop Manual which can be downloaded in 5 or 6 parts from the main page of the X350 forum.

Cheers,

Don

 

Hi Don,

Just happened to be logged on too...

The strut will be replaced 'under warranty'; so no out-of-pocket expense for me. Also, the leak is from the mounting area of the strut between the four nus, not the air-line going in to the top of the strut. Apparently, they have had a rash of bad-from-stock struts, and you don't know which side yours is on until you install.

 

Hi Na5h,

You would think Bilstein would test every shock for leaks as part of its QC process. I wish we could get some photos of the internals of these air shocks so we could understand where leaks can happen and how to diagnose the various fault modes.

Please keep us informed!

Cheers,

Don

 

Thanks to all for their input... Here's the latest: the left-front schock was replaced last Friday and so far no problems (touch wood). This would be my third shock in the same position. The indy I used said that Arnott had told him that they had a rash of bad shocks leave their property. They were not sure of the cause of the bad struts, but were looking in to it to reduce similar problems in the future...