S211 Rear Suspension Down But Pump Working

[Tom_P]

Hi Everyone,

First time posting here after doing a lot of thread trawling. Hoping someone can help.

My 2004 E200 estate (non airmatic) is down on the bumpstops at the back. It used to occasionally go down but would always pump back up again. Now it won't pump back up and it does have the warning telling me not to drive it.

I couldn't hear the pump running when I turned the car on. I checked the fuse and relay and they seem fine so took out the arch liner and connected 12v direct to the pump and it runs but doesn't lift the back. (Side note, the rubber hose from filter to pump was split). I removed the outlet line to make sure air was coming out. On disconnecting it is hissed as pressure in the pipe was released. Now when I turned on the ignition, the pump ran. The pump is definitely chucking out what seems like a good amount of air so I wondered whether a valve downstream may be stuck OR whether the pump is just not working well enough.

Is there a valve downstream that could be blocked? I might try and pressure test the pump but just as an idea, should I be able to shut off the flow with my thumb? The pump did seem to be shutting off because it thought the correct pressure was reached which seems puzzling. I only have access to basic OBD2 scanners at the moment.

Thanks in advance!

 

[AMGeed]

A Star test ( MB Diagnostics) at an MB specialist can read live data and diagnose the fault.
Be aware that if the car isn't rising and the pump continues to run you risk burning it out.

 

[Tom_P]

Thanks for that. I wanted to have a go at it first but I will head to a specialist if I need to. What is strange is that the pump is not running continuously.

 

[V6Matty]

Thanks for that. I wanted to have a go at it first but I will head to a specialist if I need to. What is strange is that the pump is not running continuously.

They are set to run for a maximum amount of time, if pressure isn’t then reached it turns off for a while before trying again

 

[Tom_P]

Ah ok thanks. Could be the case that there is just a really bad leak somewhere then. It is holding some kind of pressure as there was the release of air when I undid the line out from the compressor but that could be minimal.

 

[V6Matty]

Very likely a split in the pipe t piece that goes over the back axel, best thing to do it get a can of gas leak tester over everything to see where the leak is, after that then it’s two option, the pump has already been running on too much now and won’t produce the pressure, or the release valves are all stuck open

 

[Tom_P]

Thanks for that. I will get it up in the air and take a look and report back. I think I am right in thinking there is no valve block as with the airmatic models so any faulty valves would be at the struts themselves.

 

[V6Matty]

Correct

 

[alexanderfoti]

My 2004 E200 estate (non airmatic) is down on the bumpstops at the back. It used to occasionally go down but would always pump back up again. Now it won't pump back up and it does have the warning telling me not to drive it.

Its likely the bags have failed. If they have had an intermittent slow leak for a while, then every time you pump them up from completely flat, it damages the bags a bit.

When commissioning new bags, you must inflate them with the car held up on the ramp so that the bags are not completely compressed, and are not damaged on inflation.

If the problem is not in the bags, it will be in the line to the T junction as above, or the tops of the bags where the lines enter, but I think its more likely to be the bags at this stage, we do lots of them.

 

[Tom_P]

Really appreciated everyone's help.

One final question before I start pulling bits apart; is the t-piece only accessible from underneath the car?

 

[alexanderfoti]

It

Really appreciated everyone's help.

One final question before I start pulling bits apart; is the t-piece only accessible from underneath the car?

It is

 

[Tom_P]

So I have the car up in the air and the t-piece looks fine. I have made a schrader valve adapter to attach to the airline at the font where it exits from the compressor. I did this so i could pump it up to check for leaks without running the compressor. I just cant get any air in however. It is like it is blocked. Is it possible that the valves at the bags are both somehow closed. Is there a separate fuse for them or whatever controls them?
The next thing i will try is disconnecting one of the lines at the t piece to be sure that i can get air through but before i do that i thought i would ask about fuses. I think there is a separate fuse for the airmatic control unit but not sure if this is the same for non airmatic.

 

[AMGeed]

Fuse f45 is the airmatic fuse on a W211
Its located in the engine compartment fuse box, drivers side against the bulkhead.
f45 is the end fuse closest to the front of the car and in a line of 12 fuses. Its a 7.5amp fuse.

 

[Tom_P]

Fuse f45 is the airmatic fuse on a W211
Its located in the engine compartment fuse box, drivers side against the bulkhead.
f45 is the end fuse closest to the front of the car and in a line of 12 fuses. Its a 7.5amp fuse.

Thanks very much.
Do you know if that is the same for non airmatic models with only air springs at the rear?

 

[AMGeed]

Thanks very much.
Do you know if that is the same for non airmatic models with only air springs at the rear?

Sorry I don't. That is the airmatic fuse on the fuse diagrams I have for the W211.
Its worth checking that fuse anyway.

 

[Tom_P]

I checked that fuse, it is ok. I also found a fuse in the interior fuse box (37) that is listed as 'control unit height adjustment'. This was also fine. Next question; where is the control unit located? I suppose this could be at fault.

 

[Tom_P]

Hi everyone,
Just an update on this. I didn't manage to find a leak but a battery disconnect seemed to kick it into action again so I suspect it was something to do with the valve control.
The car is still going down a lot and more frequently so I am in the process of replacing the bags.
When I first fire it up, I know it needs to be in the air but is there anything else I need to do? Does it need to be calibrated at the garage?
I made a little tool to remove and re-tighten the air line.

 

[alexanderfoti]

Good job on the tool, we use something similar!

No, just in the air, let it add some pressure into the bags, lower it down a few inches, let it pump up, rinse repeat until its completely off the jac.

 

[Tom_P]

Thanks for your help. It has stayed up over night so fingers crossed! One side seems slightly lower but I will see how it goes over the next few days. Might have to get them calibrated if it stays that way.

Looking at the bags that came off, one looked like it was probably ok but the other had some cracks in the rubber on the fold.

One of the protective rubber boots popped off the new ones while they were inflating so I need to get this back on this morning. I went for the cheapest ones I could find (£180 for the pair!). We will see how they fair. I thought I might as well give them a go. Didn't want to spend too much as the car is just a daily hack and I didn't buy it for much!
The cable ties that hold the boots on, which have a rib running down them on the originals, are just ordinarry ones covering twisted wire on these

 

[malcolm E53 AMG]

[QUOTE="Tom_P, post: 1887697, member: 108542"

Looking at the bags that came off, one looked like it was probably ok but the other had some cracks in the rubber on the fold.[/QUOTE]

Yes this is the issue and unfortunately can’t be seen when the bags are on the car. Which replacement bags did you use in the end it’ll be interesting to see how they perform?