dannys said:

Guess what, the EAS of the 1996 DSE that I own for 5 months now has started acting up. And not in the usual way: no faults registered, no beeps and no error messages. What happened is that it would go fine and than, especially after accelerating from standstill in a traffic light, the front would kneel and would not adjust for several minutes. Out of town its bearable, but running in town means that you are nearly constantly on the bump stops. No leaks detected in the usual testing ways, so I called upon my MSV2 for help.
The nice thing with the MSV2 and my laptop, is that you can monitor the behavior of the EAS system in (nearly) real time while driving. You get a page like the one attached, EAS monitoring. As the system go through its paces, you can follow the valves as they open and close and the heights being adjusted accordingly.
It turned out that indeed, as I was accelerating from standstill, FRONT LEFT VALVE STATES and FRONT RIGHT VALVE STATES changed to OPEN for few seconds, then quickly closed. These brief seconds were enough to nearly empty the front air springs and cause the faulty behavior.
At first I suspected the ECU or the Driver pack: after all, why open these two valves when the car starts moving? it made no sense to me (still doesn't, btw). But then I looked at the air-system diagram from rave, depicted as the second attachment (Air path) here. From the diagram it immediately became clear that, even if the spring valves are open, air should not escape unless the exhaust valve is also open :doh:. On the next run I made sure that it indeed remains closed, so air must be escaping, most probably through a leaky exhaust valve. (a leaky Inlet valve would be the next bet.)
I quickly emptied the system's air, and with the valve block still mounted on the car (not recommended...) I undid the valve, cleaned it and replaced the o-rings, never to see the problem again (its been two weeks...).
Just thought I'd share this with you, and even add my conclusions: even strange and quirky behavior can, and most likely does, come from faulty o-ring in the valve block.

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wammers said:

Air cannot leak out from a faulty inlet valve only in.

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Derek Ward said:

As you accellerate, the weight transfers to the rear of the car and the front will rise. The suspension ECU hasn't a clue what you're actually doing. All it will see is the front suspension going up so it will try to let air out to compensate. I think it does open the exhaust port but only very quickly and you don't see or notice it on the laptop. Why the other valves should stay open longer I'm not 100% sure but possibly to equalise the pressures and therefore the heights across the axle?
Sound like a theory?

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dannys said:

Any reason why?

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If the EAS delay relay is working correctly normal suspension movement does not trigger the inlet or exhaust valves to open so no air is lost or gained.

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Derek Ward said:

Sorry Wammers. You're not wrong very often. But. The EAS Delay relay is nowt to do with the workings of the ECU I'm afraid. All it basically does is switch power on and off. The ECU 'averages' the ride heights when the vehicle is moving and after a period of time (which I haven't a clue how long), will let air in or out as is necessary to either maintain the ride height or adjust it to suit whatever is selected. The Delay Relay delays the power being switched off to the ECU so it can level the vehicle when everyone has disembarked and luggage has been removed. It then 'wakes up' the ECU every few hours to check the vehicle is level and if it ain't will lower each corner to the same as the lowest reading height sensor.

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wammers said:

Well basically because behind the inlet valve is 140psi of air pressure. If one of the corner valves opens and the inlet valve is leaking it can only put air into the bag, as there is less presssure in the bag than behind the inlet valve. It's almost like a none electronic zenner diode. Air can only flow one way from high pressure to low pressure. When you look at the EAS it is a very simple system of two parts. One part is the pressure supply side, comprising a compressor, a reciever and a pressure switch. When you switch on the ignition and start the vehicle if the pressure in the tank is less than 120 psi the pump is switched on until the pressure reaches 140 psi then switches off. As air is used by the system this side cycles to maintain workable pressure. The other part is the pressure distribution side. The four sensors on the axles send signals to the ECU, if that/those signal/signals is/are the same as the selected height/heights then there is no action. If any of the singals is lower than the selected height/heights. Then the ECU sends a signal to the control box to open the relivent corners valve, plus the inlet valve, air flows into the bag/bags until the sensor/sensors reach the selected height then the valves are closed. If in so doing enough air is used from the tank to lower the pressure below 120 psi the compressor is activated to replenish the tank.
If any one of the corners is too high the relivent valve is opened plus the exhaust valve and air is released until the sensor reads the selected height. If the EAS delay relay is working correctly normal suspension movement does not trigger the inlet or exhaust valves to open so no air is lost or gained.

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dannys said:

wammers, great explanation of the system's operation, opened my eyes I must say. But, the inlet valve does not necessarily have to leak to the high-pressure side in (against I should say) the normal flow path. I can also leak to the electromagnet housing via the larger of the o-rings sealing the valve to the valve block and from there to atmosphere as the housing is open. Would this then mean that the reservoir should empty as well? I am not sure which is the high-pressure side of these valves...do you know?

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eightinavee said:

I've had too much wine already to make a serious contribution,but all the talk of high pressure,140 psi tankfull of air etc is fine.BUT,all these old bangers are now at least 8 yrs old and most are in a poor state.I've got 4 in at the moment for various "issues",one of them is for EAS faults. It has the pressure signal constantly high fault - good sign of a failed drive pack,but on having a look around it when I tested the compressor the needle on the pressure gauge barely got off the stop.
Point I'm making is that with age and wear you cannot just assume that all will function as the Rave data states.Checking out height sensors is also a very important early check to carry out - many faults blamed on other things are down to them giving the same output in multiple postions.

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Derek Ward said:

It then 'wakes up' the ECU every few hours to check the vehicle is level and if it ain't will lower each corner to the same as the lowest reading height sensor.

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SpudH said:

The single worst feature of the whole set up and biggest contributor to premature compressor failure!!! A single leak can cause all 4 bags to empty every time you turn off the car for any length of time!!!

Dannys, I'd be interested to know why your compressor is not running in the screen shot. I presume the screenshot was taken with the door open hence why all the valves are shut but with the engine running then the compressor should be running unless the reservoir is full. I see the pressure switch is closed indicating that it is full but I would have expected it to be using air to try and lift it up. Also it's strange that both the rise and lower switches are showing up as 'open'.

Also there is a big difference between your target heights. I know these are reference only but when last was it calibrated?

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