EAS Perpetual Operation

Hello All,

I recently purchased a P38 DSE (1999) and all air springs but one were fine. I changed the perished spring on the O/S front and the ride has significantly improved.

However, the compressor still seems to continuously operate (15 seconds on, 5 seconds off for example). I am fairly convinced I can hear a valve opening up and letting air out of the system in stages, only for the compressor to then re-pressurise the system and the whole cycle continues perpetually.

As a consequence, the N/S front of the car appears to lower and lift continuously, but only slightly (perhaps 3cm). I need to double check whether this is happening on both front air springs. I have of course checked the air springs for obvious signs of leaks but just wondered if anyone can help to diagnose the problem?

Many thanks in advance - I look forward to hearing from you.

Cheers,

"Geordie" Paul.

Sounds like an overhaul of the Eas valve block is needed (diy job if you fancy having a go).

or spurious signal from a height sensor. I'd get the free eas software and read the codes before going further.

In this case it is highly likely you have an air leak. The sudden expelling of air is the compressor shutting down at pressure and is normal. Check the bag at full extension. The connections to it and the valve block. If no leak is found, remove exhaust filter and put a finger over port. If air can be felt coming out when compressor is off refurbish valve block.

Either the system has a leak, usually an airbag, but possibly the diaphragm in the valve block, or the pressure switch is playing up. It could also be a height sensor particularly if you stressed it when changing the airbag. You need to get it on diagnostics and also go around with leak detector, start by checking the pipe where it enters the airbag you changed.
By the way, it's not good practice to change just one, they should be done in pairs as one old and one new on the same axle could give some funny handling.

Confusing, how often do these compressors fire up, example. My whole EAS system was overhauled last year, 4 new air springs, valve block rebuilt new seals, and all ride height sensors checked and re- calibrated. If I leave my 2.5 DSE ticking over the compressor fires up and runs for about 5 minutes and then stops, I guess the air tank is full. I then leave it ticking over and whilst stationary the compressor did not fire up anymore. Now in motion of around town driving my compressor is stop, start about every minute building air up. Is this normal?? I have sometines noticed whilst stationary in traffic the occasional dip at the front and then rising to normal height and the compressor firing back up. ive had my EAS re checked and no faults all working fine, the only suspect was the compressor may be getting a little weak in age. So the question is how often should or do the compressors fire to recharge the air tank.

anorakmark said:

Confusing, how often do these compressors fire up, example. My whole EAS system was overhauled last year, 4 new air springs, valve block rebuilt new seals, and all ride height sensors checked and re- calibrated. If I leave my 2.5 DSE ticking over the compressor fires up and runs for about 5 minutes and then stops, I guess the air tank is full. I then leave it ticking over and whilst stationary the compressor did not fire up anymore. Now in motion of around town driving my compressor is stop, start about every minute building air up. Is this normal?? I have sometines noticed whilst stationary in traffic the occasional dip at the front and then rising to normal height and the compressor firing back up. ive had my EAS re checked and no faults all working fine, the only suspect was the compressor may be getting a little weak in age. So the question is how often should or do the compressors fire to recharge the air tank.

Click to expand...

The cut in pressure is 7.8 to 8 bar the cut out pressure is 9.5 to 10.5 bar so worst case only 1.5 bar between cut in and cut out. Any sort of leveling by the EAS may cause the compressor to cycle. The dip and rise when stationary can be caused by re-leveling after the foot brake is released or by a dodgy height sensor or driver pack. Probably nothing to worry about

anorakmark said:

Confusing, how often do these compressors fire up, example. My whole EAS system was overhauled last year, 4 new air springs, valve block rebuilt new seals, and all ride height sensors checked and re- calibrated. If I leave my 2.5 DSE ticking over the compressor fires up and runs for about 5 minutes and then stops, I guess the air tank is full. I then leave it ticking over and whilst stationary the compressor did not fire up anymore. Now in motion of around town driving my compressor is stop, start about every minute building air up. Is this normal?? I have sometines noticed whilst stationary in traffic the occasional dip at the front and then rising to normal height and the compressor firing back up. ive had my EAS re checked and no faults all working fine, the only suspect was the compressor may be getting a little weak in age. So the question is how often should or do the compressors fire to recharge the air tank.

Click to expand...

Every time the vehicle speed falls below 1 mph the front valves open to equalise the pressure across the axle. This is the reason that sometimes in traffic, stop, start, you will notice the front drop and then go back up. It is because there is unequal pressure in one side. Either because of bad calibration, uneven loading or the weight of the driver. Or a combination of all three.

Thanks Wammers & datatek, that answers my questions, I can rely on you guys.
I guess the EAS is always in question as it appears to be such a fragile system.
And after what I went through with mine last year i'm always a little over cautious with the system. Just one quick question Wammers, Datatek?? I have been diagnosed with a slight weak compressor and want to change it myself. It looks rather easy but do I have to de-pressurize the system before I remove the blue air line? and is there anything I should be careful with. Thanks Guys in advance as I know your advice is top notch.

No need to de-pressurize the system. Its easy to change.

anorakmark said:

Thanks Wammers & datatek, that answers my questions, I can rely on you guys.
I guess the EAS is always in question as it appears to be such a fragile system.
And after what I went through with mine last year i'm always a little over cautious with the system. Just one quick question Wammers, Datatek?? I have been diagnosed with a slight weak compressor and want to change it myself. It looks rather easy but do I have to de-pressurize the system before I remove the blue air line? and is there anything I should be careful with. Thanks Guys in advance as I know your advice is top notch.

Click to expand...

No need to depressurise. You can get a new compressor from Island 4 x 4 or you can fit a new seal and if necessary a new cylinder to your exisitng compressor

Thank you for all your responses - I haven't been able to try anything today but did notice this:

After quite a lengthy drive today I opened the bonnet and checked the compressor - it was red hot that I couldn't touch it. It wasn't running at all and I presume this was because the thermal cut-out was active. Despite this, I could still hear the valves opening and letting air out of the system, the n/s front dropping in 3 stages, and then raising again (the compressor still not running), presumably with air from the reservoir. I'll go through the checks you mention of course, but I find this puzzling.

I also left the car on extended ride height over the night, carefully measuring the height at each corner and took fresh measurements in the morning - exactly the same. The car remains at the same height.

Datatek - I take your point about changing the airbags in pairs but the other three can't be older than a couple of months at the most. I suspect the only reason the o/s front wasn't changed is because the wheel took longer to remove than fitting the bag did!

Hopefully update you soon once this dissertation is done!

Cheers,

Paul.

sirsmilealot said:

Thank you for all your responses - I haven't been able to try anything today but did notice this:

After quite a lengthy drive today I opened the bonnet and checked the compressor - it was red hot that I couldn't touch it. It wasn't running at all and I presume this was because the thermal cut-out was active. Despite this, I could still hear the valves opening and letting air out of the system, the n/s front dropping in 3 stages, and then raising again (the compressor still not running), presumably with air from the reservoir. I'll go through the checks you mention of course, but I find this puzzling.

I also left the car on extended ride height over the night, carefully measuring the height at each corner and took fresh measurements in the morning - exactly the same. The car remains at the same height.

Datatek - I take your point about changing the airbags in pairs but the other three can't be older than a couple of months at the most. I suspect the only reason the o/s front wasn't changed is because the wheel took longer to remove than fitting the bag did!

Hopefully update you soon once this dissertation is done!

Cheers,

Paul.

Click to expand...

The thermal cut-out is essentially a fuse built into the compressor motor. It does not re-set itself, it blows and then must be replaced.

With the engine turned off the car will self-level. I'll admit I don't understand the raising bit but the lowering and the valves clicking is the automatic self-levelling.

That is not correct the thermal cut out goes open circuit above 120 degrees. When the compressor cools down it returns to full continuity.