http://www.rangerovers.net/repairdetails/airsuspension/index.html This air-spring FAQ applies to Range Rovers, but this might help you guys find your problem.
Normal Operation which Might Seem Faulty: The air suspension is controlled by an ECU under the drivers seat, which operates a solenoid valve block in the engine compartment. The ECU has a fairly low IQ, and wastes a lot of air by raising and lowering each corner constantly trying to level the vehicle. So the system's compressor turns on frequently. Another cause of its frequent running is the fact that the pressure switch is located remotely from the air tank so the pressure drop in the thin air line makes it think more air is needed. Another annoying feature that is said to be normal happens whenever the vehicle is parked on anything but a perfectly flat surface. The system tries to level itself by lowering all springs to the height of the lowest one, then realizes it is still not level so it lowers the first spring as well and starts the whole cycle over again until the vehicle ends up on the bump stops. This rather unintelligent strategy is particularly annoying off pavement, since the ground is nearly always uneven. So don't park where there is a big rock or other obstacle under the vehicle! If you want to stop in such a spot temporarily, either leave the engine running, or inhibit the system's unintelligent operation by leaving a door or the tailgate open. Pressing the manual inhibit switch on the dash also helps reduce or ewliminate this behaviour. Finally, whether on or off road, the ECU often lets so much air out of the system overnight that when you come out in the morning it can take several minutes for the suspension to raise itself up again to normal height. This is not supposed to happen but often does, even though the suspension checks out normally on the dealer's diagnostic apparatus.
Air Compressor Vibration: After a while the air suspension compressor can get rather noisy due to the rubber mounts wearing out. A Service Bulletin (TEC600695, July 1995, "Electronic Air Suspension Compressor Noisy") recommends updating the compressor mounts with 2 STC 828 Rubber Mounts and 6 STC 3086 snubbing washers. The rubber mounts are of s slightly different design and prevent the compressor sagging to hit against the hard mounting surface. I had this done on my 4.0 and it did quieten down the compressor. Some years later after replacing my original compressor with a used one, I noticed it did not have the new style bushings and was much noisier. So I swapped the bushings over and it quietened right down. Loosened mounting nuts or overtorquing can also lead to noise.
Air Springs: The rubber air springs do wear out faster than the old coil springs. One symptom is the boot popping out of position, especially in cold weather; I had this happen on leaving the car outside in the desert overnight, in access mode, and the suspension took a good 10 minutes to return to normal height on startup in the morning. The rubber boot seems to mate with the top metal part of the spring somewhat like a tire bead, and will usually reseat itself after a while. Michael Azzariti pressure tested an old air spring he replaced on his 95 LWB (see replacement procedure); he pumped 20psi into it and put it into a bucket of water. Air seeped out from the top, between the metal and rubber joint. He tried a higher pressure and it sealed up.
Another problem is plain old cracks and holes developing in the rubber when it gets worn. This happened on one of my rear springs around 60,000 miles. It developed a leak large enough that I could hear the air hissing out when parked in low profile. Since the spring had to be ordered from the UK, I had to drive it around like this for a couple of weeks. I was impressed that the system put up with this situation without shutting down and reverting to the "get you home" mode on the bumpstops.
On another occasion one of my air springs got cut by a twig or other sharp object and burst (a loud gunshot-like sound) while on a 4WD trail, 400 miles from home. In this situation if repair parts are not carried in the vehicle, there is little choice but to drive on the bumpstops home or to the nearest dealer. With luck only the end of the car that has the fault will be on the bumpstops, and the other will stay elevated. In any case, the advice in the owners manual about not exceeeding 35 mph is no doubt put there to protect Land Rover from warranty or liability claims -- on good smooth highways and freeways I have been able to keep up with the traffic flow quite well.
Fixing Faults in the Field: Full details of how to recover from EAS disasters in the field are provided on the EAS Field Recovery page. The following is a brief summary only.
A hose repair kit is available from Land Rover to fix leaks in the air lines, eg when they are melted due to exhaust heat -- see the section on fixing air line leaks.
A spare rubber bladder can now be purchased from Arnott Industries or Airbag Man for about $89, enabling field repair of air springs should they burst. Or, complete spare air springs can be carried (one for the front and one for the rear). If these or other fixable faults develop (as they have on my 4.0) when you are a LONG way from a dealer, you have two choices. If you think you can fix it, do so ASAP before the EAS ECU figures out the problem and goes into the "hard fault" mode (EAS Fault message on the message center, EAS warning light on, and all EAS lights lit up on the height control). Once it does this, even if you fix the cause of the fault you cannot reset the ECU without a Testbook or equivalent on 1995-98 models. (Don't ask me how I know this!). On 1999-2002 models with the Bosch electronics, you MIGHT be able to reset it by disconnecting the battery for a while as the memory in the main engine ECU is volatile, but I am not sure if this applies to the EAS ECU.
Alert reader Ron Beckett has recently discovered that even though the ECU is in "Fault" mode, you can sometimes restore normal suspension operation (but not clear the fault code) if you can pump up the air tank to normal pressure again.
If you are in an awkward spot not suitable for repair work and want to delay the computer detecting the fault, crack open a door or tailgate as you drive along, remove the air suspension delay/timer relay from under the left front seat, or remove Fuse 17 from the BeCM fuse box -- any of these actions should freeze up the EAS and put it into a state of suspended animation til you get to a suitable place to do your repairs. If you open the tailgate, also open your windows to prevent asphyxiation.
If the problem is not fixable in the field, accept your fate, and let the computer go into fault mode. It will (best case) freeze up the suspension or (worst case) lower one or both ends of the vehicle to the bump stops. You can then drive merrily home or to the nearest dealer. The advice in the owners manual about not exceeding 35 mph under these conditions is doubtlessly put there to protect Land Rover from warranty or liability claims -- the ride on the bump stops is a bit bumpy but on good smooth highways and freeways I have been able to keep up with the traffic flow quite well.
Height Sensors: These are simple potentiometers (variable resistors). The front height sensors used on early 4.0/4.6 models can sometimes be knocked out of action by getting water inside them. This generates a suspension fault code indicating that the sensor is out of range or that a valve is stuck. The solution is to replace the sensor with the design used on later models (part number ANR 2494). Bill O'Brien reports that ride height sensors that are giving problems can be removed and cleaned. He suggests prying the back off and cleaning with carbon tet or volume control cleaner from Radio Shack. Reseal the back with GE silicone.
Manual Operation if a Fault Occurs: There are several methods of operating the suspension manually using an external compressor or jumper wires. For details see the Air Suspension Manual Pump-up page.
Manual Selection of Extended Profile: One of the petty annoyances of the air suspension is that the extended profile mode, which raises the vehicle another 1.2 inches above High Profile, cannot be selected under driver control; it can only be selected automatically by the suspension ECU when it senses the vehicle is grounded. It can also be selected by the dealer's "Testbook" to make working under the vehicle more convenient. To overcome my frustration about this, and not having a Testbook", I devised a way of raising the suspension to any desired extent manually at the flick of a switch. This method is detailed in the section on Upgrade Operations How-To.
Rear Axle Links: The aluminum eyes on the chassis end of the rear axle trailing links were prone to possible failure.
Bushings: Range Rovers have very large suspension travel, and (especially if you use your Rover off road) all this movement eventually wears out the rubber bushings used in the suspension mounts. So, the bushings should be replaced periodically. Aftermarket manufacturers offer substitute polyurethane bushings which provide longer life and "improved handling"; this is merely a code word for stiffer suspension, translating to reduced traction and a harsher ride off road. I recommend replacing worn bushings with original equipment rubber bushings to restore the Range Rover's authentic ride and traction. Remove the old bushings with a hacksaw and push in the new ones with a large vice or a hydraulic bench press. Replace the fastenings at the same time.
More air-spring links:
http://www.rangerovers.net/repairdetails/airsuspension/airspreplace.html Replacing an Air Spring w/ pics
