First air suspension issue

[M-A8]

Originally Posted by mannyo

I timed the raise from Dynamic to full lift this morning for you.

From Dynamic to full Lift took just under 30 seconds, all done smoothly in four stages, back, front, back, front.

Before the repair it took a Looooong time.

Cheers Manny
But as always I've got few questions:
30sec, is that till the white arrow up disappears or until car stops lifting??
Was that during the drive or on the driveway before you went to work this morning??

1.22sec feels like a long time in my example but even if car stopped lifting (got to the Lift mode) the arrow stayed white for good 20sec +
This could be with car being on a slight slope and control unit was just trying to get it as level as possible???

Waiting for your pressure update later on

Cheers Manny

[M-A8]

Just a quick update to what I just find out.

I spoke to best Master Technician I know from Audi and what this fella says about the pressure in that video seems to be a bit of b@l@x and is misleading.

16 bar he says=220PSI
Front tyre with max load=41PSI

That is a 5,5 times higher pressure than in a tyre !!!!!

Have you seen the air hoses on the the compressor side, even he said this would be unreal cos even on a new compressor you would be able to hold the pressure with your finger if you unclip the hose because what he says that there is an operating pressure of around 6bar when no leaks !!!!!

6bar seems to be more real than 16bar, but I couldn't really talk to him for long so I didn't asked all the questions and we didnt managed to check the pressure against any document which would give me something to compare my readings to.

Interesting

Manny's and Delboy's pressure readings should make it more clear, especially Manny's after recent fix.

Cheers boys

[HPsauce]

Those figures around 3 or 4 bar shown on screen seem entirely plausible.
You could do some "ball-park" calculations based on the size of the units and weight of the car as a cross-check.

e.g. 3 bar is 3*10**5 N/m**2 (30 Newtons per square cm)
A 2 tonne car on Earths surface will apply a force of about 5000 N on each corner, which at 3 bar needs about 156 sq cm.
If that was a disc it would be about 7cm radius, or 5.5" diameter. How does that match the lifting struts?

[M-A8]

Thats funny, just found this info in SSP292:

but this I understand is pressure value inside the springs, can you measure pressure on each spring??? I switched through all the channels yesterday and there was no group for individual springs

''Each suspension strut features residual pressure retaining valves directly at the air connection.
This ensures that a minimum pressure of approx. 3.5 bar is maintained in the pneumatic
springs. This practically eliminates the risk of damage during storage and assembly to the
greatest possible extent.''


Another interesting thing about the accumulator pressure of 16bars not the compressor pressure:

''Accumulator
The accumulator is situated between the
floor of the boot and the rear silencer on the
left-hand side of the vehicle.
Construction:
The accumulator is made of aluminium.
It has a volume of 5.8l and a max. operating
pressure of 16 bar.
Function:
The objective in designing this system was to
reliably satisfy functional requirements
whilst keeping energy consumption to a minimum
(so that the compressor is on as little
as possible). In order to enable controlled
pressure build-up to be effected solely with
the accumulator, there must be a minimum
difference in pressure of 3 bar between the
accumulator and the pneumatic springs''

>>>>>>
Final control diagnosis
Final control diagnosis checks the function of
the compressor, the solenoid valves and the
struts/shock absorbers.
Diagnosis is executed automatically in three
steps.
1. Test of each individual strut by lowering it
20 mm below its current level for a period
of 30 seconds
2. Charge and empty the accumulator
3. Variation of electrical currents to actuate
the shock absorbers
Final control diagnosis is implemented when
the vehicle is stationary and the ignition is on.
The engine may be running. During final control
diagnosis, the yellow warning lamp in the
dash panel insert flashes.

[ainarssems]

Have not seen the air pipes on D3 but brake pipes and hoses(any car) do not look too impressive however they can handle 150-200 Bar.

[mannyo]

I'll see what I can do this evening, the compressor outputs 16bar and that fills up the pressure resevoir, in turn that supplies the valve block, which feeds all four struts. So the 16 bar is used to maintain all four struts, thats only 4 bar each. The actual air needed will be less otherwise the compressor will be running pretty much all the time. I would expect to see close to 16bar at the G291 sensor, but maybe I'll be proved wrong.

[mannyo]

Right I did some testing in the office carpark before driving home.

Starting point, car has been parked all day and compressor has not yet run.

Reading


Down to Dynamic

Reading


Up to Lift

In Motion, compressor on.

Fully Lifted


If you view the attached VCDS log which I did driving home from work, you can see that the sensor does ramp up to in excess of 10 bar.

[Delboy]

Hi Mannyo,

Pressure in the Accumulator is available to any / all the struts, its not divided by 4.

Each Strut has a solenoid valve dedicated to it that opens in conjunction with the valve that isolates the accumulator.

I went out just now and tested mine, and using measuring bocks in VCDS I could see between 3 - 9 bar depending on if i was going up or down.

I did my first set of tests using the mmi to raise and lower the car with the engine off, the compressor would not run and after 4/5 up down sequences the accumulator emptied and lift was greyed out on the mmi.

Once started the compressor ran and charged back up.

All that said I found there is a better way to test and that's to go to output tests in the level control module and run them, it will go through many tests but the one that we should pay particular attention to is Accumulator test.

Unfortunately I didn't let mine run long enough and it didn't charge high enough to satisfy the test.

I will do another test tomorrow as the compressor was up to around 60 degrees after all my dicking around.

[mannyo]

Del,

I have just attached an excel spreadsheet to post 53, which is a log of the suspension activity on my drive home.