Rob P.

Yep, another suspension thread. Sunday afternoon - Red warning on the dash that the car is too low. Down on passenger front. Pump would OCCASIONALLY (like 4 times total in 1/2 hour - 45 mins) lift the front then it would go down again within 30 sec - 1 min Then no lift at all. Pass rear went down overnight. Left rear is still up as of today. Rt front is partially up but not fully up.

Things I know...

Pump does not run very long before shutting off. Car does not even attempt to lift.
Console lift button does nothing but light the button LED.
I usually run the Sporty 1 suspension setting. Changing the suspension setting does nothing.
SAM(?) relay in (engine) fuse box clicks before pump begins to run. Relay checked for function and contact out of car. Works as expected. Reinstalled, no change.
Pump does not run very often and usually for only a short time (3-5 seconds usually with the occasional 30-45 second run time).
Pump runs erratically or not at all.
I pulled the air line off the right front strut. When pump runs, I can plug the end of the plastic line with my thumb and it will not blow air past my thumb. System supposedly operates with ~10 BAR pressure (1 BAR is ~15psi so system is ~150psi) yet pressure at Rt front air line is low low low but with lots of volume.
Control valve block has 2 connectors besides air lines. 1 is a pressure switch and 1 is a solenoid. I ASSUME that the pressure switch is the pump shutoff for when system gets to operating pressure. I also ASSUME that the solenoid is the check valve to prevent the system from leaking down when the pump isn't running.
I cannot hear air leaking at Rt Front strut. I CAN hear slight air leaking someplace around the pump when it runs but can't pinpoint it because of pump noise.
Pump air line to valve block seems good. Other air lines at block also seem OK.

Things I need to know:
Am I correct about the pressure switch and solenoid?
Should the pump have higher pressure than observed?


I suspect that my problem is the pump but am concerned that the valve block solenoid is malfunctioning/leaking because car often drops on all 4 corners in less than 2 days.

So, am I on the right track?

Rob P.

I did some more checking and here's something else.

I cannot add air to the strut from an outside source. If I connect an outside air source directly to the strut no air gets through the valve at the top of the strut. If I disconnect the system air line and open a door, the air system bleeds air out of the air line to try to level the car. However, key off, key on, pump running or not, no air gets into the strut/air bag from either the system or an external air source because the valve is not opening.

This tells me that the valve is not operating.

So, what controls the air valve on top of the strut? Where is it located? How do I check whatever component that is? Does this component control the entire right side of the car because only that side is on the ground? Can I jumper/hot wire the strut to open the valve to check the air bag for a leak? How?

If the controller for the strut valve checks out, then the valve is not operating and I need a new strut. But I'm not into buying a new strut if the bad component is only a sensor or relay.

I have no access at present to any Star diagnostic so that option is out. Need to do this old school with diagrams and manual component testing. I have bookmarked the "Welcome to the w211 E-class page and am working my way through the various air system diagrams, schematics, and components but a bit of help pointing in the right direction would be appreciated.

RJPerls

Howdy Rob P

Welcome to the world of MB pneumatic suspensions. Great idea but sure seems like MB suits forced cheap materials to market.

A few months ago both front air-springs on my E500 crapped out at 30K miles.

There are several common failure points:

1) Air-spring "air bladders"-- these are more like rubber tubes rolled into themselves.
The elastomer is under great stress and fails both by mechanical fatigue and by the elastomer becoming brittle over time- which of course leads to mechanical fatigue.

2) Air pump failure- usually the pump wears out and it can't make the required PSI and or air volume in an allotted time. This is often brought on by the bladders developing tiny but manageable air leaks but the air leaks jacks the duty cycle of the tiny air compressor and it pumps a lot of air and soon wears out.

Other variants like air pump relay, nylon hoses rupturing, pressure sensor, diverter valve, suspension computer; air valves in springs, level sensors, accelerometers and air reservoir failing are less common.

You just have to have a look-see around this site to discover how common the air suspension failure really is- and not just on the W211 series.

There are two controls on the air manifold-- one opens a line to the air storage tank that's located somewhere in the rear portion of the car-- that's just a solenoid. the other module is a pressure transducer. It's a fairly complex solid state transducer which sends an analog signal back to the suspension computer that's proportional to the air pressure applied. All air lines are tied together in the air manifold.

The air-springs have two valves-- one opens to a chamber that supplies added volume for more cushioning; the other opens to the "air bladder" itself. I'm not certain how the two cambers are interlinked. Depending on how busy the suspension is the suspension ECU will either add or subtract the extra air volume from the spring.

The valves are controlled by solenoids with a common line and two individual lines for each air chamber. I activated the solenoids by using a 12V battery with a series 10 ohm resistor to limit current flow through the solenoids. With the series 10 ohm ballast resistor the solenoids suck down about 1/2ampere. I was able to inflate the airsprings by activating the proper solenoid and of course applying controlled compressed air to the air input. I used an external compressor with it's own pressure regulator. My air-springs didn't inflate-- the air just rushed out of the bottom vents.

You can not be certain that the suspension computer will allow you to inflate the air bladders because a fault could be pending and the computer will not activate the suspension. Also the suspension control algorithm is undoubtedly complex so many inputs have to be "proper" for the ECU to "co-operate".

You CAN trouble shoot the system w/o the MB Star. It's just much quicker (and easier) with the MB STAR.

Hope this helps a little.

Good luck

RJPERLS

cmriv

DAS/Xentry guided tests. Sounds to me like a strut is implausible, valve block leaking, pump faulty. Could be 1 or a compilation of everything. All of your knowledge on this system is irrelevant until you find someone with MB specific diag equipment...

Rob P.

Thanks for the information so far. I've got a compressor coming because I still think the compressor is not functioning properly and a new one will either confirm that theory or can be considered preventative maintenance.

I'm still looking for a diagnostic flow chart for the components. These are usually logic circuits so I can't just use a test light to check for voltage at the plugs. I need a real diagnostic chart which can give me test procedures and values.

I can't seem to find a factory service manual except the "index only" CD's on ebay that need an internet connection to the actual manual. Anyone know where they are available?

cmriv

The diagnostic flow chart is embedded in DAS and Xentry....
You are replacing parts that may not even be faulty but like you said preventive maintenance. I would just be bummed if the pump isn't the issue... back to square one...

Rob P.

I made the decision to replace the pump after careful thought. I only recently bought this car and have already experienced some very clever and careful coverups of failed systems (my SRS airbags being bypassed for instance) rather than the previous owner actually repairing them.

So, I believe that changing the pump is worth the price because now I KNOW that the pump hasn't been burnt out because of a faulty OEM relay and then just the relay was replaced.

If the system still won't lift the car, I will have to take it to a shop that can diagnose the problem and provide me with an estimate for the repair. The outcome from that will determine if I keep it or not.

Rob P.

Updating thread.

Ordered a Rebuilt Master Tech pump. Half the price of OEM, Suncore, or Arnott and I get $25 back for the core. Changed the pump today. It works now and car lifts.

But...

Right front strut still has a problem. The dreaded air leak whistle as the car settles back onto the suspension bumper.

So, RMT is going to get a call for a strut. Nice timing though, 10% off for Halloween.

cmriv

You are setting a good example for me to learn from. My 550 has 98k miles on the clock. If and when any of my airmatic components fails-i'm immediately converting to coilovers.

Rob P.

I thought about converting to coilovers but decided not to. If I wanted coil springs I would have bought a C class.

And, here's another consideration: A coilover kit is ~$1500 plus installation. 2 RMT struts and 2 rear airbags are slightly cheaper and I don't have to modify the car with non OEM spec parts and play the "trial and error adjust the ride height with spacers" game. And, in my case, the rear bags were recently replaced by the prior owner so all I have to do is the fronts anyway.

The only major bugs I have left to worry about are the SBC and rear shocks. Well, that and regular maintenance items (though I have gotten the ESP malfunction warning a couple of times. Which may or may not indicate that I will be replacing the ECU at some point too). So most of the high ticket repairs will be done soon.

And, knowing what I know now, IF I'd purchased the car new(er) I would budget for replacement pump/struts/bags/shocks and get that done proactively at around 80-90K. Spread the cost out over 1-2 years and that's not much pain to the monthly budget. And, the car is not out of service while at the repair shop for weeks at a time, plus towing, plus car rental, plus, plus, plus...

cmriv

Touche', however I work on MB's for a living. So no labor for me, and even so I couldn't see a shop charging a arm and a leg to install coil overs on a 211, these suspensions are extremely basic, air or coils. - BC racing coils 900$-E350 rear LCA's 150$ bucks from a junk yard. so 1150$ to convert and no after market parts except the coils themselves.. If you use a ruler and measure the height of the coils before installing there is no trial and error. Find out what spring rate you'd have-vehicle weight-4 corners + or - passengers.... do some math and you could simply figure out what your ride height will be prior to installing.

Also: you could of bought a c class if you wanted coil springs OR you could of bought a E class w/o airmatic....

Only downside to converting would be getting an alignment. Only con in my opinion but to each their own!

Rob P.

Ok last update and this thread can go to archive.

I ordered a new strut last week from RMT. Arrived yesterday. I took the day off from work expecting it to take all day to replace the strut.

Wow, was I wrong. From sticking a jack under the frame to final torque of the lugbolts was about 1 1/2 hours.

I have no idea why people are afraid to do this repair. Granted, my 320 is RWD and different from 4matic but still...

FIRST THING is to remove the relay for the air pump. Then, stick a jack on the jacking point that's under the door & on the car frame. Remove the wheel. Lift the car and stick a jackstand under the rear inner suspension pivot. Remove the front belly pan. Loosen the 3 nuts at the top of the strut remove 2 of the nuts so that the strut can hang from the 3rd if necessary. Disconnect the air line and the electrical plug. Undo the 1 bolt at the bottom. Remove the 1 nut for the inner fenderwell right in front of the upper suspension bushing. Follow the wire from the lower control over the swaybar, and forward behind the fenderwell. Remove the plastic bracket that holds the electrical connectors you see behind the wheelwell under the frame rail by popping the round "rivet" out of the frame and dropping the bracket. The loose inner fenderwell helps let you get your hands in there - it's tight.

Remove the male end of the plug on the wire from the strut and then slide the female end of the plug from the bracket. Undo the 3 torx headed bolt/nuts holding the upper ball joint to the uper control arm. Pull ball joint free from the upper control arm (it just slides out) but keep hold of it so you don't overstress the wires and brake line. At this point the strut is ready to pull out so remove the last nut at the top of the strut, compress the strut and lift it off of the lower control arm and swing it to the rear. Drop the strut down and out of the wheelwell.

Assembly is reverse order though I did have to use a pry bar to push down on the lower control arms to let the lower end of the strut clear the arm and go into position. Check your upper ball joint for wear while you have it out. It should be a bit stiff to move. Mine needs replacement (it's kinda floppy) but that's a job that can wait. The only caution is that you NEED TO USE LOCKTIGHT ON THE UPPER CONTROL ARM TORX BOLTS.

So, all of you who are putting off this horrible, awful, painful, and expensive job - don't. My strut from RMT was $375 plus core deposit. Free return shipping too. That and 1 1/2 hours of not very physical labor with common garage hand tools and my 320 is happy.

Once it was together it stood right up and leveled itself. Next month is the left front strut's turn.