Still got issues on 2007 E class estate rear self levelling air suspension.

[Baldbloke]

The ECU/controller is N97 and it's in the passenger footwell. Wiring diagram says there's a 4 wire connection from that to the rear axle level sensor.

Cheers, I think I saw it when I was checking the run of the air feed pipe inside the cabin.
Now I’m wondering if the new airbags are too short to give adequate ride height. Elegance models are not covered by the Arnott coil spring conversion kits as they would ride too low. Elegance is specifically excluded. The eBay seller reassured me the Luftmasters I bought do all the wagon models but I’m beginning to have my doubts when my model of car obviously has some differences. He assured me the suspension units would adapt to suit any difference.

Do you know if air pressure has any bearing on the suspension, or is it all down to ride height?


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[andym2]

From what I can see the controller can only adjust ride height by adding or releasing air, and it aims to keep the 'at rest' height at what it thinks is level. So for a given shock 'at rest' length the pressure will increase to match the load. In case it's of any use to you, here's a wiring diagram for the N97 Rear suspension controller...

 

[Baldbloke]

Ok, here's an update. I had a bit of a fiddle with the help of a mate whose got a better understanding of electrics.

What I did was to crawl under the car again with the ride height controller disconnected from the car's bodywork and anti-roll bar. My mate started the car and while I was underneath I adjusted the position of the controller arm until the compressor started up and the airbags began to extend. The axle stands were underneath the very ends of the rear wishbones so emulating the weight of the car's rear end.
The ride height came right up to where I wanted it, but the lever angle I had it at would not have been possible had the unit been in position and properly bolted to the car. Perhaps that's why I've got precisely nowhere so far as a mere fitter of parts. By manually operating the arm it was down at 7 o clock, rather than where it wants to be which is at about 2 o clock in a more upright position. With the controller off the car and being manually twiddled, the compressor began to run and the air bags rose to the correct ride height. However the position I was holding it at would have required the plastic arm of the controller to have been touching the drive shaft or differential had it been bolted back in place. That is just not practical. The compressor even stopped once the ride height was right up. I thought we were eventually getting somewhere. Then my mate closed the drivers door and the compressor vented air and the suspension went down again. There must be some fairly complicated safeguards in place with associated wiring.
So the new compressor is up to the job (albeit taking around a minute to get there) and the air suspension bags appear to be able to extend to an adequate length, but the controller seems to need to be calibrated by about 180 degrees to allow the arm to operate within its proper constraints, and send the correct signals while bolted correctly in place.

Any ideas please?

 

[andym2]

A daft question perhaps, but if it needs to change by 180 degrees, is something either upside down or round the wrong way? Does the arm come off the sensor so it could be turned round or anything?

 

[Baldbloke]

A daft question perhaps, but if it needs to change by 180 degrees, is something either upside down or round the wrong way? Does the arm come off the sensor so it could be turned round or anything?

Good thinking, but I don’t believe so.
The electric plug is on the top of my sensor and I have looked to see if it was possible to mount it upside down too[emoji3]


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[andym2]

Is this the badger?....

 

[Baldbloke]

Is this the badger?....

View attachment 85180

Yes. Looks exactly like that[emoji1303]


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[Baldbloke]

Yes. Looks exactly like that[emoji1303]


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Ok, been away for the last three days but got back into the workshop today for a couple of hours. Here’s what I found. Remembering:

Everything was renewed with the exception of the wiring and the small bore pipe work. But I have carefully checked for leaks.

I’m suspecting the new ride height sensor is either needing programmed to suit or it’s faulty.
I stupidly renewed it, the compressor, its filter and the relay all together, rather than separately and seeing what happened.
So I replaced the ride height sensor for the old one and loosened the clamp on the roll bar to adjust it. Turning it so the arm was vertical with the engine running immediately raised the suspension. It went up to 17” above the centre of the wheel hub giving about 5” of clearance between the top of the tyre and the wheel arch. A bit too much clearance but at least it can do it[emoji1303]
I then brought the sensor arm back towards where it should sit on it’s cutaway and started the car again. It dropped about an inch and has settled there.
I ran out of time after that but will clamp it up later tomorrow and report back.
Looks like it was a compressor fault in spite of the apparent lack of wear on the bore. Maybe burnt out due to running too long and replacing the bags should hopefully correct this.

Also spotted another brake pipe needs renewed. Why oh why don’t Mercedes put a join at the the front floor before the pipework disappears up the bulkhead?

I can live in hope that my woes is down to the new sensor. Thank you for all your help and input.


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[Baldbloke]

It does appear that either the new sensor needed programed in,or it was faulty.

Car now sitting at 14.5 inches from rear hub centres to middle of wheel arch. Gives about 3" clearance between top of tyre and wheel arch lip.

Absolutely perfect. Thank again for all your input!

I now have a brake query after replacing one of the rear brake lines I'll start a new post

 

[Baldbloke]

There is a problem I'm missing.

The car sat on axle stands for four days at the correct ride height. The jacks were under the outside ends of the lower suspension arms to emulate sitting on the wheels. I measured the clearance each day over four days to ensure that the car didn't have a leak or settle. It didn't move at all, and would have given about 3" of clearance between the tyre and the wheel arch.

That is until I replaced the wheels and the car was on the ground..... Then the compressor dumped some air and the car has settled back down at a low stance and won't go back up.

I did notice there is a ride height sensor on the R/H front suspension. Could this have something to do with it in spite of not having air suspension to the front?

 

[millo777]

The level sensor on the front right hand upper wishbone is for the headlight levelling only. As far as I'm aware it doesn't have input to the suspension height.

 

[andym2]

The rear level sensor is also used by the headlight levelling for Xenon headlights. Does that still work? This doc might help, though don't know if it's correct or applies to your car...

 

[Baldbloke]

The level sensor on the front right hand upper wishbone is for the headlight levelling only. As far as I'm aware it doesn't have input to the suspension height.

Thanks Millo. I’m learning something new each day[emoji1303]


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[Baldbloke]

The rear level sensor is also used by the headlight levelling for Xenon headlights. Does that still work? This doc might help, though don't know if it's correct or applies to your car...

That is fascinating Andy. I didn’t realise there were so many interactions between doors being open, light level and ride height sensor etc. Also the lock function.

Just reinforces the need to get it on Star or something else that can read the faults and/or recalibrate the level.

I know the bags can pump up and retain air so that at least is a start.
The car does have xenon lights but I haven’t driven her at night since the current issues so cannot state whether the lights are adjusting to compensate for the back end being down.

Very interesting that it allows differing functions for the car being jacked up so allowing the wheels to be unloaded. Perhaps I’ve inadvertently confused the system with my multiple lifting up of the car.

Once I get her to suitable diagnostics, and the issue is corrected I will report back. Thanks again for all your assistance. It’s much appreciated [emoji1303]



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[andym2]

That is fascinating Andy. I didn’t realise there were so many interactions between doors being open, light level and ride height sensor etc. Also the lock function.

Just reinforces the need to get it on Star or something else that can read the faults and/or recalibrate the level.

I know the bags can pump up and retain air so that at least is a start.
The car does have xenon lights but I haven’t driven her at night since the current issues so cannot state whether the lights are adjusting to compensate for the back end being down.

Very interesting that it allows differing functions for the car being jacked up so allowing the wheels to be unloaded. Perhaps I’ve inadvertently confused the system with my multiple lifting up of the car.

Once I get her to suitable diagnostics, and the issue is corrected I will report back. Thanks again for all your assistance. It’s much appreciated [emoji1303]



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This is a bit of a bodge but something to try perhaps... When the wiring broke in the compressor connector on mine it didn’t deflate, it just put the warning on the dash. I drove it round like that for weeks, until I got the new connector to fix it. So, if you can get it to inflate then disconnect the wires from the compressor before you put it back on it’s wheels it might stay up. It’s the two (thin) wire connector on the compressor, in the near side wing, in front of the wheel. Might make it drivable.

Also, if you put some weight in the boot then wake up the self levelling does it start the compressor?

 

[Baldbloke]

This is a bit of a bodge but something to try perhaps... When the wiring broke in the compressor connector on mine it didn’t deflate, it just put the warning on the dash. I drove it round like that for weeks, until I got the new connector to fix it. So, if you can get it to inflate then disconnect the wires from the compressor before you put it back on it’s wheels it might stay up. It’s the two (thin) wire connector on the compressor, in the near side wing, in front of the wheel. Might make it drivable.

Also, if you put some weight in the boot then wake up the self levelling does it start the compressor?

I’m actually thinking of trying to get some high pressure tubing and manually inflating the bags through that valve I bought


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[Baldbloke]

I’m actually thinking of trying to get some high pressure tubing and manually inflating the bags through that valve I bought


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The car always fires up the compressor each time the car starts. Trouble is it when it’s up it then stops and dumps air until it’s lower than it should be.

Good tip about the disconnect [emoji1303]


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[andym2]

The two wire connector is for the relief valve (22) which is controlled by the ecu. There's also an over pressure valve (20), that I believe is not ecu controlled, it's just set to 10bar or whatever the max safe pressure is. I think there's also a max run time for the compressor. So, if it stays up with the 2 wire connector unplugged then the problem is the ecu venting air, probably needs the level sensor calibrated. If it still drops then probably the overpressure valve is venting. that could be a faulty valve in the compressor or an air spring that's too short, requiring too much pressure to get to the right ride height when loaded. There wasn't a spacer or rubber block or something like that on the old air shock that's not on the new ones, or anything like that is there?

 

[Baldbloke]

The two wire connector is for the relief valve (22) which is controlled by the ecu. There's also an over pressure valve (20), that I believe is not ecu controlled, it's just set to 10bar or whatever the max safe pressure is. I think there's also a max run time for the compressor. So, if it stays up with the 2 wire connector unplugged then the problem is the ecu venting air, probably needs the level sensor calibrated. If it still drops then probably the overpressure valve is venting. that could be a faulty valve in the compressor or an air spring that's too short, requiring too much pressure to get to the right ride height when loaded. There wasn't a spacer or rubber block or something like that on the old air shock that's not on the new ones, or anything like that is there?

All very helpful. Thank you.

Interesting you mention the possibility of the air bags being too short and needing to much air
Pressure to attain the correct ride height.
I did send two emails to the seller asking if they might be too short. I specifically mentioned that I couldn’t use the coil spring conversion offered by Arnott as they said that solution wouldn’t give adequate ride height, so had concerns my Elegance model might need taller air bags. However, the seller reassured me he’d sold hundreds and that many would have been for my model with Zero returns.
I did email LuftMaster who also said the bags were correct.
I have also seen more than adequate ride height, and sustaining that ride height for days sitting on axle stands nearest the wheels. Because of this I believe the seller. However on jacking the car off the stands and putting wheels back on the ride height dropped as soon as I started the engine. It’s not right down and not putting up a warning message, but it looks too low.
I have an old Porsche I’ve been working on for a few days prior to an mot tomorrow, so once that’s on the road I’ll get the Mercedes somewhere for a read of fault codes or hopefully a recalibration if possible [emoji1303]


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[Baldbloke]

There wasn't a spacer or rubber block or something like that on the old air shock that's not on the new ones, or anything like that is there?

No, but I did notice that the replacements were 28cm and the originals were 31.5 cm with the valves removed. I told the seller about this but he assured me that the ride height sensor would determine the final height and that the bags had adequate length to give the correct height. This I believe as I’ve seen the car raised to well above what’s required.

Hopefully a recalibration is possible, and I will write the final solution up so others don’t have to go through my experience.

Many thanks for the ongoing encouragement!



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