Don, Nice summarization, iam getting ready to set up a good air suspension testing setup. Do you know the thread size of all the connections on the valve block in the trunk?
My plan is to hook up a air compressor to each line in the trunk to find leaking struts and also to the reservoir and valve block itselft to check if maybe the valve bllock itself is leaking.

 

Hi SJ9809,

My recollection is that the front air spring hose fittings are 1/8 inch BSP (British Standard Pipe) thread, which has an external thread diameter of 9.6 mm or 0.38 inch (just slightly larger than 3/8 inch). The front air hoses are 6 mm O.D.

The rear air spring hoses are 4 mm O.D. and the fittings are a different size. I think one of our members figured out that they are 5/16 UNF ((British) Unified National Fine) thread fittings, but I may be wrong.

These are not sizes you are likely to find in stock in a hardware store in the U.S. However, I believe I ordered them from McMaster-Carr (mcmaster.com) to build pressure gauge test rigs based on lcmjaguar's design.

For some helpful info on using gauges to test for leaks, see this post from lcmjaguar:

Air Suspension Test Gauges For Loan from lcmjaguar

Cheers,

Don

 

Ok, I finally got all the parts to pressurize the system with my Air compressor.
I basically disconnected every loop in the trunk and pressurized it with about 8,5-8,9 bar (all my compressor can do) then i disconnected the air compressor using a small valve and watch for pressure drop on the gauge.
I did this with all four struts and there was no noticeable drop.
I did the same test with the reservoir to make sure that this is not the leaking component, no drop.
After that i also disconnected the air compressor from the valve block, closed the loop with the valve and manually run the air compressor for a few seconds, turned it off and looked for a pressure drop on my gauge in the trunk... no drop.

After that i actually pressurized the valve block with all hoses disconnected, and whatever input i tested (all other loops connected, battery of car disconnected) the pressure dropped pretty fast is this normal, is the valve block in the trunk supposed to leak? I also disconnected all other lines and did the same test again, whatever inlet i pressurized it dropped very fast from 8 bar to 2,5 bar.
Maybe i need a new valve block, i saw that amazon sells these and in the reviews quite a few people stated that this was actually the leaking component.
Would be helpful to know how this valve block works, i was assuming that without power basically everything is closed which would mean that i dont get a pressure drop when i pressurize any inlet!?

Some pictures of the test setup attached...
1. pressurize inlet of reservoir connection, all other loops are connected


2. test of a strut loop (rear strut)

 

Just want to give an update and a short explanation of my process.
i finally got everything fixed and the Air suspension works great!!! I turned out to be a leaking valve block in the trunk.

Here is my recommendation how to test the air suspension, in general i would say the Air suspension is actually a very easy design and not that difficult to diagnose if you know what you are doing.
Here is how i did it:
1. Cut all the air lines 4mm/6mm in the trunk (underneath spare tire), before you cut you can release air by loosing the nuts on the valve, or just cut them.
2. Get simple 4mm (x3) and 6mm (x3) Push to connect fittings from Festo or other places i reference McMaster part numbers (McMaster: 5225K61, 5225K62), with these fittings you can put all these lines back together
3. To build a test gauge you need the following parts if you do it with an standard (Home depot, Loewe, Menards....) Air compressor:
- 6534K56 Quick disconnect 1/4 for air compressor connection, 1/4NPT thread for fitting
- 5225K713 (fitting goes into the quick disconnect coupling with 1/4NPT and on the other end you have 6mm push to connect for the air tube)
- 50315K24 5 ft (or whatever you like) Ø6mm Festo or similar air tubing
- 4379K71 push to connect shut of valve 6mm
- cut some from the 6mm tubing just 2 inch or so
- 5225K804 Tee fitting for integrating a air pressure gauge (2x6mm + 1/4 NPT male)
- 50785K92 (connector 1/4 NPT female to 1/4 NPT female) for attaching the pressure gauge to the Tee fitting
- 4089K81 pressure gauge with 1/4 NPT male
- optional attached another 5 inch or so, Ø6mm tubing you have to the other Tee end via push to connect (only for comfort so you can check the pressure gauge in a comfortable position and not down in the trunk.
- to test 4mm lines (rear struts and compressor input) you need also a push to connect reducer from 6mm to 4mm ( 5225K946)
Now you have all the parts and i list them in the order they are basically put together.

Test procedure:
disconnect one of push to connect connectors that you put in the air-lines in the 1 st step, if you already have an idea which strut is leaking start with this one.
-Disconnect the connector in the trunk and connect you Ø6mm tubing that is hooked up to the air compressor to the line going to the strut. For rear strut you have to use the 6mmto4mm reducer fitting), make sure that the valve is closed.
-when everything is connected turn On the valve and fill the loop up with air, when you have about 8 bar (my air compressor only made about 8bar you can easily go up to 10-12 bar, official test pressure for the struts is i think 40 bar!), when you reach the air pressure then close the valve and watch the pressure gauge if the pressure drops fast you have a leak, it shouldnt really drop at all, not sure if anybody has exact parameters. In my case i watched it for 30-60 second and there was no noticeable drop.
- when the tested loop passed than disconnect it and test the same llop in the other direction (not the strut, but the connection to the valve in the trunk and the valve it self) basically the same procedure.
THIS IS VERY IMPORTANT, because in my case it turned out that i had a massive pressure drop here and that way i found out that my valve block is the actual problem that causes the Air Suspension to fail because it was leaking a lot. (4-5 bar in 30 seconds)
- with the method above you can also pressure test the air tank, which i believe is very uncommon to leak, but just in case to go save....

To test the air compressor i actually used the same test gauge but to test it you dont use your air compressor.
You can still use the same test fixture, connect it to the 4mm compressor input line and leave the Valve always closed, once everything is connected open the hood and take out Relay R1 and jump connection 3-5 with a small wire, the compressor should start running. Let it rund until the pressure gauge in the trunk shows 12-14 bar (dont jump the relay longer than 2 minutes to avoid overheating the compressor), once you reach the test pressure "turn off" the compressor by removing the wire, you shouldnt get a noticeable pressure drop, if you get one you know that something with the compressor is not right (stuck exhaust valve, or just another leak)

As i mentioned with the above procedure i was able to find my leak quickly which turned out to be the valve block in the trunk, i got a new one at amazon for $130, it is not OEM and the aluminum block is a slightly different design ( i actually like it more, because it makes it easier to connect air lines), althoug it is made in china it seems to work fine, i dont have long-term data. I think you cannot by the single valve from Jaguar, they only sell the complete unit with tank about $800? But iam not sure on that.
---- jaguar part C2C22909
the valve block comes with all the connection nuts and compression sleeve to connect the air lines, when you replace the valve make sure that you connect the air lines in the same order.
From Driver side (Left steering wheel)
Rear driver side (4mm), compressor input (4mm), reservoir (6mm), front passenger (6mm), rear passenger (4mm), front driver (6mm)

Other notes:
- I bought rebuild struts from RMT mastertech, they all worked fine, the warranty is useless if you install them yourself, they only honor their warranty if you get them installed by an ASU certified mechanic. Replacing struts on a Jaguar XJ8 is usually very easy and straight forward (except if the strut bolt is badly corroded, then it easily turns into a nightmare, especially when you do it in 10 degrees F, h0ow should i know!?)
RMT mastertech also sells the
- it doesnt mattter for this procedure but i was looking for that information and couldnt find it so i write it down for the records.
for the 6mm lines it is a standard 1/8NPT thread
for the 4mm lines it is a BSF (british standard fine) 5/16 thread, very hard to get adapters or anything, maybe a 5/16 UNF works but if you look at the pitch and thread size it is a little bit different, i could imagine that some teflon-band can makle up for the different... HOWEVER I CANNOT CONFIRM THIS!

I love my air suspension, and next time i get "Reservoir plausibilty error" I know what to do!

If you have any questions or suggestions let me know!

 

All very good, and I appreciate it's hard to differentiate valve-block leakage from the other things.
BUT, "Cut all the air lines"...can't you find a less intrusive way, such as unscrewing the fittings or something?

I can pretty much guarantee that not many people would want to "Cut all the air lines". Which (not to put too fine a point on it) might make the advice useless?

Let me put it even more succinctly. If I put my car in for professional service and found it all cut up with god-knows-what fittings, I might be a bit pissed that it might smack of amatuerism?
Your turn

 

I do understand the hesitance to “cut” the airlines. Another way is to work with thread adapters that match the Airline fittings, while that is no problem to find adapters/connectors for the 1/8 npt (reservoir and front strut) I couldn’t find any adapters/connectors for the 5/16-BSF and I didn’t want to try to yank in 5/16-UNF and risking to destroy the fittings.
When you take of the air lines and want to connect them to a push-to-connect you’ll find out that you have to first remove the compression sleeve and with the smaller ones most likely you will break it. (I did) RMT sells new VOSS fittings. But it’s $15 each. Couldn’t find these kind of compression sleeves.

In my opinion putting FESTO push to connect fittings in their is not “whatever” fitting, these fittings are used on every industrial machine that has pneumatic or vacuum functions. I think it would absolutely makes sense to put these in there from the beginning for easier maintenance. But I don’t think that so many Jaguar engineers thought about nor were willing to spend money on making it easier for customers to diagnose the Air suspension.
Even when you buy Air line repair kits they come with a push to connect fitting.
I do agree with you that some kind of cutting lines and put a connector in between sounds not so much professional, however in this case using well-proved and widely used Festo push to connect fittings is not unprofessional.
I put them in one of our customer assemblies every day, this assembly goes into a 1million Dollar medical scanner.
Our company make populated cable tracks with cables and hoses, when we have small air/vacuum hoses (up to 10mm) the most common thing is to put these push to connect fittings on both ends, once the customer gets our product the only have to push in their hoses and they are ready to go.

 

Hi SJ9809,

Thank you for your enthusiastic diagnostics and for reporting your efforts and results here!

I don't know why Chris always has to be so rude and superior, but he almost raises a valid point, and that is the pressure rating of the FESTO push-in connectors. The ones I used for my test gauge setup (modeled after the one lcmjaguar created) are rated to only 150psi. While the manual states that the nominal operating pressure in the air springs is 7-9 bar (101.5 - 130.5 psi), the pressure in the reservoir is typically 9-15 bar (145 psi - 217 psi), and the "full bump" pressure in the system can rise to has high as 20 bar (290 psi), presumably when a tire impacts a pothole or speed bump, for example (see pdf page 10 of the manual). This is the reason I did not permanently insert push-in fittings into our air suspension piping. Are the connectors you used rated for 300 psi or higher? If they're rated to only 150 psi, you will need to be concerned about long-term reliability.

My real question for you is, where was the air leaking from the valve block? The system is designed with only one official exit point, which is the exhaust solenoid valve on the compressor. Could you tell where air was actually escaping from your valve block?

P.S. I will probably move your posts to start your own thread to make it easier to find in searches.

Cheers,

Don

 

The connectors I used are rated 290psi. (See McMaster link)
the tubing I used is actually a little bit underrated but there ist always some safety build in 😉… and if it bursts I will just buy new one… i just had tons of this 4mm and 6mm tubing (10bar rated) at work. And struts usually don’t go over 10 bar. The air compressor line and valve to tank line go i think up to 14.4 bar but also only for a few seconds and than the solenoid closes so Iam not that concerned. And if it bursts I will by higher rated tubing installation is really not difficult, for now It just happened that I am trying to keep the costs low.

i don’t know where it’s leaking I actually plan to get it underwater at some point just out of curiosity

 

G’day all. I had a suspension fault it was losing air after a time. Took it to Jag dealer here who couldn’t find it as the fault code was stating leak at reservoir but it wasn’t leaking. They left the car plugged in and UK dialled in and found that it was the compressor leaking. All fixed $180 it was just a lose connection. Sometimes it’s just worth the money to get the dealer to fix it.
keep happy
james

 

Depends $180 is a lot of money for me… wouldn’t be happy to pay that for a loose connection. Which is probably 10minutes to fix it.

But I do understand the happiness of the air suspension fix is only $180…

 

I'm glad your push-in fittings are rated to 290 psi. The hose rating of 10 bar may be of concern though. Remember that the Wabco (not Jaguar) engineers who designed the system anticipated that the maximum system pressure can reach 20 bar / 290 psi when a wheel hits a hard bump. This pressure increase in the air spring as it compresses is transferred right up the air hose to the closed valve in the valve block. If one of your hoses bursts while driving at speed it could present a real safety issue.

I will be very curious to learn where your valve block was leaking. Thanks again for sharing your diagnosis and repair. I'm going to create a separate thread for you to make it easier for others to find with the search engines.

Cheers!

Don

 

Exactly this question crossed my mind when reading your post, I'm curious to see what the underwater test will proof.

Thanks for the write-up,
Fritz

 

Hi guys iam back...
and guess what i got 3 days of driving without Air suspension fault... first i was , but then i said to myself calm down you know now how the system works and you will find the fault...
Fortunately it didnt took long. Because of the leaking valve block the Air compressor never made it over 12 bar before it switch off with the Air suspension set to error. Now with the fixed valve block and a leak free system the Air compressor was forced to work and make more than 12 bar. For about two days it went up to 14 bar. Then it got significant colder here in Wisconsin about 25 F in the morning. The Air compressor barely made it to 12,5-13 bar, I watched the pressure sensor while driving using the carsoft i930, Air suspension, data stream, Pressure sensor. So i parked the car and hooked up the i930 and ran the compressor manual by jumping the relay, with this procedure you can basically test the performance of the Compressor and check if there is any leak in the compressor loop, since you jump the relay the car system still thinks that the compressor is off so it does not open the solenoid in the Reservoir to get filled up. Thats why this is a good procedure to test the compressor easily just with a piece of wire. It turned out that the compressor made it up to 13bar and thats it, even if i let it run for another minute its not going over 13 bar and thats why i got the error code.
I took the compressor out and the air-line connection was pretty bad and totally worn out. I think at this point the rebuild kit doesnt really do anything. I did the rebuild last year with the Piston ring...
So i need a new compressor, i did order an aftermarket for $180 and installed it and works fine it goes up to 15 bar in no time... we will see how long it lasts. On all my cars i made good experience with aftermarket and at this point i just didnt want to spend $500, and the one i bought comes with 10 year replacement gurantee (from AutSchack), we will see.

With all that i also wanted to check the old valve block and i put it under water.
When i pressurize the compressor inlet air comes out on all the other outlets which shouldnt be the case, if the valve block is without power everything should be closed.
When the Air compressor runs their should be air going from compressor to the Reservoir outlet. The single strut valves get feed with air from the Reservoir only when the compressor is off.
So what i think happend here that the some valves within the block got stuck and the compressor inlet never closes completely.
Iam not 100% how the valve block is designed inside and how it works in detail, maybe somebody knows more here???

 

Saw some venders that sell the piston ring with a new head.
The bore was scored, from the ring not being replaced on mine.
Saw this after replacing the compressor..
Being a pack rat with my used parts, i replaced the head & ring in my old compressor.
Being from China the price was attractive enough to try, the parts look good, & fit.
Not yet installed but it's ready to try if & when one is needed.

 

I LOVE the bubble bath!
Wouldn't that mean most of the suspension was going uncontrolled up rather than down?
(or randomly up or down? Or working apparently fine except for a bit more use of the compressor or release?)
I don't know. I'm asking :-)