Disco TD5 Air suspension problem

First time poster, long time reader of this site. But please, before I get the inevitable sighs of "another bloody airbag problem" please read on.

I had the usual dropping suspension, both sides. After much research into issues and causes etc, trying to find a cheap quick fix (Im a yorkshireman, therefore Im tight), I came to the inevitable conclusion that it was my airbags. Soapy water confirmed the suspicions. However, I had the issue for a week or so before I could order and receive the parts, and had to use the car a couple of times. The suspension would lift and hold. A couple of minutes after engine was turned on, the suspension was a proper ride height and off I went. It held sometimes for a few days, sometimes for 30 mins once engine was off (as in most of the many posts I read). I also noted that after the suspension was charged up, the compressor didnt need to work very hard at all to maintain it (really small leaks/perforation of the bags) and I kept use to a minimum to avoid wearing out the compressor. Then one day, after it had held the height for at least 2 days, I got 100 yards down the road and the suspension just dropped, faster than it ever has before. Read: dropped.

I managed to limp back home and onto my drive. I wouldnt normally have done that but as it was a main road and I was 100 yards away I did, at 2 mph. Much to the annoyance of the rush hour traffic.

However, I jacked the chassis up onto stands so the car was not resting on sunken airbags and left it until the new bags arrived. Now, Im not new to doing this kind of work so was confident I could do it, and I wasnt wrong. Especially with the research I had done from this site and the great information I got before hand. Battenberg, youre a star for your threads, amongst others. I even ordered 4 new clips on your advice and despite not needing them, felt better putting new ones on.

Now, with new bags installed, pressured up and sitting in the correct position, I proceeded to remove the supporting jack and expected the disco to take the weight and the right height to be achieved. The compressor had filled the bags, the folds on the bags were right and it seemed like I could take the dog out again. But no. Not tonight. I removed the jack and the car sank. And kept sinking. Until it hit the jack which was fully contracted. I can hear the compressor working (well, its putting air in the bags, that I can be sure of) and can see the bags inflated. But not holding its own weight.

This is the thing. The compressor kicks in as soon as the engine is running and seems to run for a while, then stops. Even if I jack the car up to close to the right height, it does the same. Then sinks. I have checked the new connections to the bags and the bags themselves and no leaks are apparent. Surely if the air is leaking then the compressor will run continuously? It seems to reach a predetermined pressure and then stops. I dont know, this is why Im confused. But it wont take the wieght of the car, at all.

Anyone got any clue what this could be or where to start? It got dark then and my hands have frozen cos its so bloody cold. So, Im not using the car for a while longer - and driving an 08 Vectra just doesnt have the same charm. In fact, its the most boring car I have ever driven. Please, help me get back in a proper car again!

Sorry for the essay, but I thought I should explain everything. Thanks in advance for any responses/ideas/help. Muchos gracias.

I forgot to mention but dont know if its anything to do with it. But the entended ride height mode has never worked, or Im not doing it properly.

When I press the button, I get 3 chimes, and thats it. No raise, nothing. Is it anything to do with the above problem or something seperate?

check out all these possibilities........just to be sure http://www.landyzone.co.uk/lz/f8/saggy-arse-102185-2.html#post1043200 and

The SLABS ECU receives a continuous battery supply from fuse 11 in the engine compartment fusebox. An ignition
'ON' signal is supplied from the ignition switch via fuse 28 in the passenger compartment fusebox. The ECU has the
ability to control when it requires power and is not reliant on the ignition signal for it to power up.
The ECU incorporates a counter which times the operation of the SLS system and prevents the compressor
exceeding its duty cycle. The ECU can remain powered for up to 1.5 hours after ignition off is sensed to allow the
counter to continue running to avoid an ignition cycle resetting the counter.
Opening any of the doors will power up the ECU, irrespective of ignition switch position. The door open signal is
sensed by the door switch completing an earth path which is sensed by the ECU. The ECU cannot differentiate
between any of the doors. The door open signal powers the ECU for up to 30 minutes to allow the vehicle to re-level
when a load is removed or passengers leave the vehicle. The ECU supplies a 5 V current to each of the height sensors. Each height sensor uses the current to supply an
analogue input to the ECU. The ECU can calculate from the input received from each height sensor the height of the
vehicle and can then power the air supply unit as necessary to raise or lower one or both air springs to level the
vehicle.
When SLS compressor operation is required, the ECU provides a battery supply to energise the SLS relay located in
the engine compartment fusebox. When the relay contacts close, a 12 V supply passes through fusible link 9 in the
engine compartment fusebox, through the relay contacts and operates the air supply unit compressor. The ECU will
then supply power to operate one or both air control valve solenoids and/or the exhaust valve solenoid to inflate or
deflate the air springs as required. The compressor does not need to be powered to deflate the air springs.
The ECU also controls the operation of the SLS audible warning, the SLS warning lamp and the ORM warning lamp.
When the ignition is switched to position II, the ECU performs a three second bulb check and illuminates the SLS and
ORM warning lamps in the instrument pack to check for operation. When the system is operating or a fault is sensed
by the ECU, the ECU will operate the appropriate warning lamp and audible warning as required. The audible warning
is operated by the Body Control Unit (BCU) when it receives a signal from the SLABS ECU. The audible warning is
emitted from a speaker at the rear of the instrument pack.
Depressing the ORM switch for a minimum of 0.5 seconds, completes an earth which the ECU uses as a signal to
initiate the ORM if conditions allow. When the ECU starts ORM, the same earth that was completed by the ORM
switch is pulled to earth by the ECU to activate the ORM warning lamp. The ECU checks for a further operation of the
ORM switch by continuously and very quickly removing the earth for the ORM warning lamp. If the ORM switch is
operated for more than 0.5 seconds, the ECU will detect this and de-activate the ORM.
The SLS part of the SLABS ECU also uses the road speed data generated within the SLABS ECU by the ABS system.
Operation of ORM and extended mode are road speed sensitive and use the ABS signal to monitor the vehicle speed.
When the accessory remote handset is used for the SLS lower and raise functions, the handset transmits RF signals
which are received by the same RF receiver used for the alarm/remote door locking system. The RF receiver passes
this data as a 25 Hz PWM signal to the BCU. The BCU then transmits this data to the SLABS ECU as raise or lower
data. TestBook is required to program the BCU for remote handset operation.

discodoobie said:

I forgot to mention but dont know if its anything to do with it. But the entended ride height mode has never worked, or Im not doing it properly.

When I press the button, I get 3 chimes, and thats it. No raise, nothing. Is it anything to do with the above problem or something seperate?

Click to expand...

I'm assuming that you have ALL doors shut when you are doing these tests? Otherwise the system will not hold up.

Incidently, are your interior lights working normally? The sls system appears to get a trigger signal via the BCU that the doors are open or shut, so if there was a fault on the courtesy lights it might be sending a bad signal to the BCU??

cheers for the responses guys.

Im just reading all your info sierrafery, seeing if any of it applies and what I can do. I will post back as soon as I have gone through it all.

As for your question biglad, yeah, all doors are closed and all lights work as they should. That much I understand. Just reading up on the saggy arse stuff now to try make sense of the rest.

The biggest mystery to me is how the system 'appears', or at least sounds, like it was working just as before the airbags needed replacing. I open the door, turn the ignition, close the door. The compressor kicks in and bags inflate. This happens now. Except now, while on stands to not allow the car to sit on the new bags, the bags inflate to the point where you can feel the tension in the sides of the bags. However, when the weight is taken on the bags, it just slowly drops.

I had the same problem once and it was the pressure limiting valve, I found a used one cause I couldn't find the code of it, it does not appear on the catalogues...........locate it and verify with some lather.

Two thoughts - check there aren't any leaks round the air pipe unions to the new bags - a leak there might well present like this.

Another possibility (other than the valves in the compressor box being stuck/leaky is that the air pipes themselves have worn through somewhere. Bit coincidental being at the same time as the bag change so I'd still suspect the leaks round unions. If you depressurised the system by undoing the unions to the valves in the compressor block check they're nice and airtight.

David

sierrafery said:

I had the same problem once and it was the pressure limiting valve, I found a used one cause I couldn't find the code of it, it does not appear on the catalogues...........locate it and verify with some lather.

Click to expand...

Im just about to go and check the whole compressor setup after reading and double reading all the advice and info I have found since (the rain has just stopped for a few mins, Im going to take my chance).

I was trying to locate the pressure limiting valve on the picture Battenberg put on his 'definitive guide' thread and couldnt find it. However, Im sure I will be able to find it once Im looking at it. Any advice on what to do with it once I have found it would be much appreciated.

David - Ive checked the unions as a matter of course when I first fitted them and tested them. I didnt see the point of putting wheels back on without doing that first at least. However, Im now going to get fully under the car and trace them back to the compressor box, do a full check.

I will post with any new findings. Any other suggestions of what to look for/check would be greatly appreciated too as I will keep checking back here for bits of info.

good to see i am not the only one with this fault

drewster said:

good to see i am not the only one with this fault

Click to expand...

good? its extremely maddening!!!!

ok, no air leaks so far, doused everything i can see and nothing.

problem im facing now is getting the compressor box off. there are 2 bolts holding it in place and 1 is a 13mm and the other is 10. is this normal? i doubt it.

however, if you are looking at the passenger side of the car, its the left hand one that is 13mm and is also just turning in its position. Not tightening or slackening. Grrrrr.

I think the thread has come loose from the plastic case and its just turning. any ideas on how to get that out.....?

Ok, so after much head scratching (ok, hair pulling) and lots of soapy water, there are no apparent leaks.

I cannot free the compressor housing as that bolt is just turning in its position so I have not been able to spend too long trying to free it. I might need to think about this one.

The air has stayed in the bags since the new bags went on, still nice and tight with the pressure holding to a certain extent. Car still wont stand up.

The pressure limiting valve was not leaking, but would a good bash help it out? The compressor still pumps when doors are closed, but stops after a while. Then the car sinks and I can still not find any leaks.

I am working on it alone atm tho, so dropping the car on the jack, listening and looking for leaks and everything else I am trying to check on a gravel drive is not easy!

However, if its worth anything, the compressor (dont know which part as I cant get the box off) is making a slight noise. When I turn the ignition off after trying to get the bloody thing to stand up, there is a small 'buzzing' or similar noise coming from the unit that I only noticed when the cover was removed and my head was next to it. Could that be anything? Even though nothing showing up with soapy water.

I even tested the soapy water was working too!! Ive also used Gas Leak Detector spray (which is glorified soapy water) as Im a plumber, still nothing.

discodoobie said:

...........that bolt is just turning in its position so I have not been able to spend too long trying to free it. I might need to think about this one.

Click to expand...

I'd say you don't have to think to much.........cut it down and you'll find a way to fix another one............the last method is to solder a nut to the chasis. Remember Murphy's law..... "if it's not working take a bigger hammer"

I had the same problem with the bolt spinning.

Fortunately, I was replacing the entire compressor housing, so I had to be less careful than you do ;-)

The problem is that the bolts screw into a brass insert pressed into the plastic compressor housing - the bolt corrodes to the insert, and when you apply enough force, the brass insert ends up spinning around in the plastic housing.

I angle ground the bolt head off, but the heat destroyed the plastic of the compressor housing, and it came apart that way. I'd advise against doing the same if you intend on still using the compressor. That said, I didnt know the individual components of the compressor housing (compressor, valves etc) were available separately from LR so I would suspect you might have to suck it up and get another one?

On another note : It might be worth having a quick look at the ride height sensors with Nanocom etc to ensure they are reporting sensible values - if one had gone crazy, perhaps the car thinks it is too high so is deliberately deflating the bags?

David

David Pye said:

That said, I didnt know the individual components of the compressor housing (compressor, valves etc) were available separately from LR so I would suspect you might have to suck it up and get another one?
David

Click to expand...

Well, its looking that way. With the car not even driveable, its a case of finding someone willing to come here to read codes etc. I dont want to have to replace the compressor only to find out its the ride height sensors, or the other way around to be honest.

Its looking like thats the only option though, unless someone can think of any other issues I might not have checked for.

I cant understand why the compressor would only pump for a short time though, well, I say short. It pumps air into the bags and keeps going for a different amount each time. However, its doesnt even try to take the weight of the car or hold it up once pressure is in the bags. But the fact it stops pumping means to me something is telling it to stop. I dont know, Im going to get this bolt off and see what I can do.

Thing is: If the bags are inflated, sure they will sag a bit when the cars weight is put on them but if they are deflating completely, then that has to be a valve/leak in the air hosing, rather than the compressor. The compressor shouldnt be 'holding the weight of the car' - the valves should be holding the air in the system, so if it is being emptied by the car weight, valves/air tubing is where the problem ought to lie.

Re the compressor stopping - the ECU will limit the compressor's duty cycle to prevent it burning out (not always successfully it seems!) - I can't explain why it would stop after a different length of time each time though.

If you put your location in your status, then you've got more chance of someone offering to pop by

David

Thats exactly whats puzzling me. Im assuming if the compressor is knackered, then it wouldnt pump air at all. But it is.

Im also assuming its a valve that is either stuck open or a leak in the air pipe, but the compressor isnt running as long as it did for the few times it had to inflate the bags from the lowest they could sit. That maybe took 2 or 3 minutes from fully deflated to sitting at ride height. The compressor wont run for that long now, or wont carry on inflating once the bags are at a certain pressure. Something is making it stop. But also, nothing is making it carry on pumping either.

If the readings from the ride height sensors are wrong, then would the ECU keep the exhaust valve open? Or could it stick open? I dont know what 'type' of valve it is either.

Im struggling to get the bolt off without causing damage to the compressor housing too. Grinding is probably the best way, but as you said, you were replacing the housing.

You might be able (with a LOT of patience) to hacksaw the head off the bolt and lever and pry to get the compressor housing off the chassis brackets that way?

Either way, the brass insert that is pressed into the compressor housing is knackered from the position of being able to do it back up - you will need to use a washer and a nut behind it in future.



I don't know much about the valves myself to be honest - unsure whether they are available separately etc - I don't think they are from LR but dunno whether they are any other sources such as Wabco or equivalent parts from RS etc. I don't see why they couldn't stick open, and it would make sense to me that a faulty ride height sensor (so the car thinks it's way too high) would make it keep the exhaust valve open to try to drop it back down. Perhaps you can test them with a multimeter - I'm not really sure. Would be worth looking at the RAVE cd to see what voltages they output. I know they receive a + volts supply at their connector from the loom - again, checking RAVE and getting a multimeter might be able to confirm to you that the voltage is at least being supplied to them?

David

This doesn't sound like a compressor problem at all to me. The pump is not there to support the weight of the vehicle at all and is designed to run in short bursts only, when the ride height needs to be corrected or when the offroad switch is selected.

So don't expect the compressor to support the car.

I believe there is an issue with your ride height sensors giving dodgy info to the sls ecu, which is opening the valves.

If it was me and I couldn't get a Nanocom or similar onto the car I would change the ride height sensors £18 each, immediately.

thebiglad said:

This doesn't sound like a compressor problem at all to me. The pump is not there to support the weight of the vehicle at all and is designed to run in short bursts only, when the ride height needs to be corrected or when the offroad switch is selected.

So don't expect the compressor to support the car.

I believe there is an issue with your ride height sensors giving dodgy info to the sls ecu, which is opening the valves.

If it was me and I couldn't get a Nanocom or similar onto the car I would change the ride height sensors £18 each, immediately.

Click to expand...

It's a good advice my friend but the ugly part is that if you want to be sure that the job is well done you also need a testbook to calibrate the sensors...........unfortunately everything is leading to a tester.

sierrafery said:

It's a good advice my friend but the ugly part is that if you want to be sure that the job is well done you also need a testbook to calibrate the sensors...........unfortunately everything is leading to a tester.

Click to expand...

Not so, ensure the vehicle is on level ground and the vehicle itself is level before starting.

Take the battery negative off, then remove the old and install the new ride height sensors, then reconnect the battery and you will find no further calibration is neccesary.