Mods, not sure if you want to throw this into the already existent threads on this topic, but...

2004 XJR, 72k miles, bought it 5 months ago with 67k. Car has been running pretty well, got an oil change 2 weeks ago, they recommended I replace the control arms, but did not. Car showed no signs of anything wrong with the suspension, but when I got into it the other day, the front right let out that hissing sound that seems common, coming from around the wheel.

The car gave me the red "Vehicle too low" and "air suspension fault" warnings, and as I backed it up, and turned the car, I could hear the tires grinding on the wheel wells as the front of the car was much lower than it should be. I am waiting to take it to a mechanic I can fully trust, and wanted some opinions from the folks on here. What seems to be the problem usually, air compressor, struts, springs, something else? Could this have been because I didn't replace the control arms? Thanks for all and any help!

John L

 

Probably air compressor needs rebuild, but should get codes pulled to be sure. If rebuild needed, get bagpiping Andy's rebuild kit. It takes longer to take the compressor out and back in than it did to rebuild it. Search on here for threads about the rebuild. It's pretty straightforward.

 

Thanks anindyam! Just searched for them on ebay, listed at 25 pounds, but it did mention if the car is sinking and/or the light is consistently on, than there is another problem which needs to be addressed first before the rebuild. Guess I better just get the codes read.

 

Hi John,

Your questions have all been dealt with in many of the other previous air suspension threads, but I'm happy to try to distill the information for you.

First of all, it is unlikely that your Vehicle Too Low (VTL) and Air Suspension Fault (ASF) warnings have anything to do with not replacing the control arms, so don't worry about them (yet).

The hiss of air you heard may very well have been the exhaust valve on the air compressor opening to back-flow dried air through the air dryer bed to partially reactivate the desiccant beads. That's part of the system design and is completely normal.

The most common causes of your symptoms are a combination of two issues: 1. A worn piston ring/seal in the air compressor, and 2. A leak somewhere in the air suspension. When the car sits, the air leaks out of the suspension, often at just one corner, or both corners of the front end but not the rear end. Less often the entire car will lower.

You can test for air leaks by spritzing a little soapy water on the air hose fittings on the tops of each air spring/shock unit and around the perimeter of the circular recess at the top of the air spring. Bubbles indicate a leak. Take care to not wet the CATS electrical connector in the center of the circular recess. If you don't find any leaks at the tops of the shocks, test the fitting on the air compressor (behind the front bumper to the left of the radiator as viewed from the driver's seat). Also test all the fittings on the valve block and air reservoir, which are in the trunk under the spare wheel and a sound-dampening foam cover.

The front air springs are easy to check because their tops are readily visible with the hood open. To access the rears you must pull away the molded/carpeted trim panels, which may require removing the trunk floor panel (two Torx screws, one in each tie-down handle), plus one plastic press rivet near the tail light on each side.

If you don't find an air leak at a hose fitting or the top seal of an air spring (which is around that circular recess), start the engine and wait for the air compressor to run and shut off (typically 120 seconds). Shut off the engine. If the VTL warning was still present on the dash, wait 45 seconds, then restart the engine and allow the compressor to run again until it shuts off. The VTL warning may go off. If not, repeat the wait/start engine/allow compressor to run cycle one more time. Shut off the engine and step out of the car and listen near each wheel for the sound of air escaping from the air spring. If one corner of the car has not raised after two or three cycles of the compressor, it is possible the air spring bladder has ruptured so badly it cannot hold any pressure.

If your air leak is slow and running the compressor two or three times extinguishes the VTL and ASF warnings, then replacing the piston ring/seal in the compressor with Andy's kit may solve most of your problem. I rebuilt our compressor and have been living with a slow leak in the front right air spring top seal for three years and it only bothers us on cold days below 40F when it can take a couple of compressor runs to raise the car.

Note that if you put the transmission in gear before the air compressor has started to run it will not start until the car is moving at 25mph or faster; and if the compressor starts but you put the transmission in gear before it automatically stops, it will stop immediately and not restart until you're moving at 25 mph or faster. So if you notice the car sitting low or the VTL or ASF warnings when you start the car, wait to put it in gear until the compressor has run its full 2-minute cycle, and if necessary shut off the car, wait 45 seconds, then restart and wait for the compressor to complete another cycle until the warnings are extinguished. It is important to wait 45 seconds between each run to avoid overheating the piston ring and cylinder head in the compressor - there is no thermal cutoff in the system, only the programmed timeout after 120 seconds.

You can download the Air Suspension/ECATS section of the Dealer Training Manual here:

http://www.mediafire.com/download/7r...on_Section.pdf

If you decide to replace the compressor piston ring, the photos at the links below will show you what's involved (most owners don't bother to replace the desiccant beads as I did so don't worry about that):

http://www.jag-lovers.org/snaps/snap...?id=1392905469
http://www.jag-lovers.org/snaps/snap...?id=1392845191
http://www.jag-lovers.org/snaps/snap...?id=1392839130
http://www.jag-lovers.org/snaps/snap...?id=1392825133
http://www.jag-lovers.org/snaps/snap...?id=1392814031
http://www.jag-lovers.org/snaps/snap...?id=1392752921
http://www.jag-lovers.org/snaps/snap...?id=1392738954


Please let us know what you find.

Cheers,

Don

 

DonB, you rock

 

I couldn't agree more, you're the man Don! So I tried turning it on and off, letting it run for a few minutes at a time, but to no effect. I'll go through those suggestions for sure.

However, I'm thinking it might be smart to just do the conversion, unless it's just a real simple fix. I've searched the forum for the different conversions, and it appears Arnott and Motorcars Ltd. Are the 2 main options. However, I haven't seen a post about it in a little while and am wondering if there are better options around and what the concesus on them both are. I'll let you guys know what ends up happening and what the mechanic says to help future jag owners!

 

Actually, Don, I just read about the recent conversion you did with Arnotts. Was there a verdict on them?

 

Just so you know...

I recently replaced my 2004 xj8's air suspension with Suncore coil overs ($999 off ebay with an $80 credit for returning the old bags). Man these things are super stiff! I'm talking 1984 Toyota 4wheel drive stiff. But it handles like a race car. Other members have said the Arnotts ride about the same as the air bags (within reason of course) so I'd spend the extra $300 and get those instead. Mine no longer rides like a luxury car but freeway on-ramps have never been so much fun! Looking for that silver lining I guess.

 

I did the conversion on a friend's 2004 XJ8 and only drove it for 5 or 10 miles after the conversion, so I don't have a lot of experience with it. But my brief impression was that the ride was very nice. It seemed a little softer over sharp bumps compared to the Sport suspension in our 2004 XJR, and it also seemed to allow a little more body roll, but not objectional at all and probably very similar to the standard Comfort suspension in the XJ8 and other non-sport models.

I might miss the self-leveling when the trunk is loaded with heavy luggage, which I really appreciate with the air suspension since we take several road trips per year. I don't know if I would miss ECATS much, but I might. My overall impression was that I could get used to the Arnotts quickly and easily be happy with them.

One important thing to note is that Arnotts includes a small device they call the "Electronic Bypass Module," or EBM, which fools the car's systems so various Air Suspension and CATS faults won't be triggered when the Air Suspension Control Module (ASM) is disconnected. This is important on certain model years but unnecessary on others, so check with Arnotts. As of the last time I checked, the Suncore kit does not include a means of preventing fault codes once the ASM is disconnected.

Cheers,

Don

 

Quick little update, tow guy just hauled it out. Getting it out of my garage and going down the curb was a nightmare, even with me going gingerly it bottomed out pretty bad. As I turned the wheel to the left, nothing was too noticeable, however, as I turned to the right and moved the car forward, there was an awful grinding noise.

I keep seeing the Arnott conversion kit for $1,220 online, and am pretty sure I'll be going with that. Now just hoping the guy is reasonable with labor costs! I do want to thank you guys for all the input, it's helped quite a bit!

 

Good luck. Have heard good things about the Arnott coilovers, but haven't had to make the switch myself yet.

 

I started getting the air suspension fault a couple years back when the weather got really cold (below freezing), I bought Andy's kit for the compressor and it fixed the problem for a year or two until it re-occurred this year. My car had 147k and I figured that my shocks were in need of replacement as a matter of routine maintenance anyway so I decided to replace the front shocks, along with all of the bushings, bearings and the wishbone control arms. My rear shocks seem fine so I left them on for now.

I looked into the coilovers, but decided against them because I wasn't sure how the ride would turn out-- and my mechanic's advice that since so much is integrated within the suspension system, other issues might arise. I went with the Arnott air suspension replacement units at about $800 for the pair, rather than the Bilsteins which are much more expensive.

While I understand you lose the CATS with the Arnott units, they seem to operate the same as they did in the past as best I can tell.

Whichever way you go, you want to be sure you have an experienced mechanic that knows how to work with the Jaguar air suspension system. It is different; and it can be seriously problematic with the electronics if you don't know what you're doing. I also understand some of the coilover units will give a continuous air suspension fault message after installation, so you want to resolve that issue with the manufacturer before buying them.

Good luck. Keep us posted on your progress. `

 

Dan,

Thanks for the input. I am definitely re-thinking my choice to switch to non-air after hearing about how it's not all that expensive to replace the air struts. Funny enough, I was just coming on here to talk about my experience with Partsgeek, who sold the Arnott conversion for $1220.

I didn't notice on the site, but it said that it came with instructions on how to disable the "air suspension fault" warning, which I took to mean it came with the EBM, which of course it didn't. Furthermore, there were no instructions. After being on hold for 20 minutes, the rep came back on the line only to be disconnected, and when I called back, they were closed for the day. In all fairness, the shipping was free and the part arrived in only a few days.

My mechanic has experience working on a few XJRs, and he said those who have done the conversion with him have generally been happy. Maybe it's the fact we are just rubes here in Las Vegas He is currently working with his assistant Mr. Google to see how to turn off the warning light without the EBM. As I mentioned before, I am definitely crossing my fingers a bit, which I know is never something you want to do with a jaguar, and this is also the first performance car I've ever owned.

 

Well good and bad news. Got the car back, but found out there has been a flat tire which the mechanic did not tell me about. Its on a donut now and only drove it 5 miles so far. Can definitely tell it's different. The jury is out for now, so once we get some new tires and let the suspension break in I'll give a final verdict.

Without the EBM, does anyone know how to bypass the CATS warning? I think Don posted something, but it was if you had the EBM

 

Hi John,

When I converted a friend's XJ8 with the Arnott kit, I measured across the four leads of the EBM in each pair combination, testing for resistance, induction, diode behavior and capacitance but only found resistance across two leads. I was hoping to find that the EBM was made up of simple components like resistors and capacitors that would be easy to replicate, but no such luck. Arnott wisely molds the EBM into a solid plastic block to prevent curious experimenters from discovering their trick.

Maybe if someone gets the Arnott kit with the EBM but discovers they don't need the EBM for their model year, they can cut the EBM open to see what the circuit(s) look like.

Cheers,

Don

 

Probably a silly question, but is it absolutely necessary to raise the car to remove/install the compressor? Is the compressor accessible just by removing the splash guards, or maybe driving the front wheels onto ramps?

Just got Andy's kit and figuring out the procedure for this...

 

I did my compressor work with the front wheels up on ramps. No need to raise the rear end. I think the photos I posted the links to earlier in this thread show which splash guards need to be removed for access.

Cheers,

Don

 

There's a very easy way to disable the faults since you have a 2004. You'll need to pull the back seat out to disconnect all the harnesses from the suspension module and then disconnect the battery for 5 minutes to reset. The shop that did my conversion disconnected the module but forgot to do the battery reset.

 

Hi Torrid,

As I replied in another previous thread, my understanding is that your statement was true of '04-'07 cars with their original software programming, but that on cars that had received a software upgrade at the dealer the module and battery disconnect might no longer fool the system and the air suspension fault would be triggered. If you know different, I'd be happy to be corrected.

I disconnected the battery on the '04 XJ8 while I converted it to Arnotts, but not knowing whether the car had received the dealer software upgrade, and not wanting to reinstall the wheels and take the car off the jack stands and drive it to find out if a fault was present, I was happy to install the Arnotts EBM as a precautionary measure. See this post from Doug at Arnotts from January 2016:

How to disable "Air Suspension Fault" after Arnott conversion


Cheers,

Don

 

That's quite possibly true, I'm not sure. My car hasn't received any updates while I've owned it but I don't know for sure that it hasn't had any and in that same regard I haven't had any experience with known updated pre 2007s. If I had the EBM when my car was converted I would have used it as a precaution as well. I don't believe the EBM existed when my conversion was done.