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Steve M

Rear suspension drops randomly

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Hello everyone,

 

After fitting a new Aerosus compressor to my FY12 F11, I've noticed that it randomly leaks air once the engine is switched off (it's possible that it leaks air while I'm driving but I've never heard it over the noise of the engine). It only leaks for 2-3 seconds so the back doesn't drop completely, then I'll hear the compressor run for a bit a few minutes after I next start driving.

 

I had one of the bags replaced at the end of last year and it seems to drop down equal amounts on both sides, so I don't think it's them. I thought it may have been a faulty relay (I swapped the relay when fitted the new compressor) so I put the old one back in but it made no difference.

 

Does anyone have any thoughts as to the cause? I'm pretty sure it didn't happen before I replaced the compressor.

 

Thanks,

 

Steve

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On 6/11/2018 at 9:01 AM, Steve M said:

Hello everyone,

 

After fitting a new Aerosus compressor to my FY12 F11, I've noticed that it randomly leaks air once the engine is switched off (it's possible that it leaks air while I'm driving but I've never heard it over the noise of the engine). It only leaks for 2-3 seconds so the back doesn't drop completely, then I'll hear the compressor run for a bit a few minutes after I next start driving.

 

I had one of the bags replaced at the end of last year and it seems to drop down equal amounts on both sides, so I don't think it's them. I thought it may have been a faulty relay (I swapped the relay when fitted the new compressor) so I put the old one back in but it made no difference.

 

Does anyone have any thoughts as to the cause? I'm pretty sure it didn't happen before I replaced the compressor.

 

Thanks,

 

Steve

 

Hi, this is probably the normal functionality of the system. Once you park the car and open the driver's door or tailgate, an amount of pressure in the air suspension system is released to equalise the pressure in the system. Mine does this nearly every time I park it in the garage. Here's a link to the detailed description of the system including how pressure is maintained/released:

 

https://www.newtis.info/tisv2/a/en/f11-530d-tou_201007/wiring-functional-info/chassis-suspension/electronic-ride-height-control/2coth0kK

 

 

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@Matthew Ashton Thanks for your reply.

 

I may be imagining it but the ride can feel a little hard for the first minute or so of driving, until the compressor pumps the bags up again. Do you also find this?

 

I'm wondering if I should take it into to have the sensors re-calibrated as suggested at the end of the article as it seems odd that so much air is let out when I get out only to be topped up again when I next set off.

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58 minutes ago, Steve M said:

@Matthew Ashton Thanks for your reply.

 

I may be imagining it but the ride can feel a little hard for the first minute or so of driving, until the compressor pumps the bags up again. Do you also find this?

 

I'm wondering if I should take it into to have the sensors re-calibrated as suggested at the end of the article as it seems odd that so much air is let out when I get out only to be topped up again when I next set off.

 

The calibration will only set the ideal ride height but no harm in trying and it is easily done with ISTA and an Enet cable (I’ve played around with mine using ISTA). 

 

I havent noticed any hardness when driving off and off and can only imagine you’d notice it if the car was sitting on the rear bump stops so in effect no air spring at all. Can you measure the “sunk” height and the normal driving height to get a feel for how much the suspension is moving when charging/discharging? I just use my fingers between top of tyre and wheel arch and mine may drop by a fat finger measurement. 

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BMWs are designed to exacting and extreme tolerances in terms of their engineering and refinement and you use a 

 

1 hour ago, Matthew Ashton said:

a fat finger

 

to measure something.

 

I dunno.;)

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3 hours ago, 535i Andrew said:

BMWs are designed to exacting and extreme tolerances in terms of their engineering and refinement and you use a 

 

 

to measure something.

 

I dunno.;)

 

My fat finger is very scientific I'll have you know! :-) 

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I had a split bag, passenger side last year, and had both replaced with Aerosus bags.

 

All has been good since then, but as per OP I also hear the compressor run briefly and pump up the bags at almost every start.

 

On Monday the car was jacked up to have two new rear tyres fitted.  When the car was lowered back down, the rear passenger side was completely down with the wheel virtually touching the arch - the drivers side looked relatively normal.  I feared the bag had split again, but once the engine was started it pumped right back up and seems fine again since.

 

Question is, do I need to be worried?  Is it normal for one bag to completely deflate when a tyre is changed???  Perhaps the excessive inflate/deflate on that side caused the original bag to wear prematurely.  I'm not sure if there's an underlying issue here, or whether I'm just being paranoid!  Can't hear any hissing at all.

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@Matthew Ashton When I mentioned that I thought the ride is sometimes a little hard, I didn't mean as hard as the car being on the stops - I experienced that when the pump gave up and it's nothing a bumpy as that! It just feels as though the car isn't as smooth over bumps as normal for a minute or two (perhaps until the pump gets the right pressure in the bags).

 

Anyway, took the car into a local BMW independent as I was passing the other day and he didn't think it was anything to worry about although he did say that it's best to recalibrate after fitting a new pump, so will get him to do that with the next service as I don't have the right equipment.

 

In the meantime, I decided to take a look to be sure no air was leaking. Jacked it up to remove the cover and it was very high when I dropped it back onto the wheels but it released the air after a few seconds to bring it down to the normal level. To test it out, I sat in the boot with the engine running and the pump kicked in - got out and some air was released. I checked the air lines and couldn't feel any air so got back in the boot and the pump went off again. Got back and the air was released.

 

So, I'm inclined to believe that it's normal functionality.

 

Hey ho!

 

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I came out to a low rear end yesterday morning, and had a 50 mile drive to get home; the drivers side rose fine, but the passenger side stayed low. I got an error message, and when I started the car I could hear the air escaping. Luckily the previous owner had given me a brand new air spring, so I got that in last night. An ok job, took well under an hour. This morning the rear end is as high as it was last night, so no deflation overnight. I did use plumbers tape on the connector though, as I wasn't fully convinced of its airtight construction. All good now though. 

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4 minutes ago, sshooie said:

No need for ptfe but it won't do any harm. 

Ah I forgot to explain - when I undid the air line there was a compression fitting on the line that needed to be removed before I could slide the screw-in piece from the line. The compression fitting snapped in 2, so after much thinking/improvisation I thought PTFE might do the job instead - or at least assist keeping the air line in place. Worked like a charm!

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Had the same issue on my 2012 F11.  Car would intermittently sit on the stops for the past year until a month ago when they failed completely.  Compressor would not kick in.  Replaced bags with Arnott units from Germany (bags were split)  but still wouldn't lift.  Transpired the compressor was only pressurising to 10 bar instead of 60 bar (I think the pressures are correct, apologies if I'm wrong!). Replaced the compressor and had the codes cleared, now works fine, although it did cost me £1000.

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