aebarto11

I just wrapped up on a multi-part suspension overhaul on an 07 4.2 (sport suspension). Everything went like clockwork until calibration and the test drive. I had been having minor issues over the last 3 months which I'll spare the long details and fast forward to the issue.

Items replaced:
- FR strut (Arnott - new) - replaced in July
- Air Compressor (Wabco - new) - just replaced
- Valve Block - just replaced
- Intake Filter - just replaced

Sorry for the novel, but important details....

No leaks from struts, valve block, or compressor. I went through calibration fine, except the RR always seemed to stay about 10-12mm lower than the LR. My height setting is 11 so I'm running at 20mm lower front and rear. I ran the calibration about 15 times, entering the true values from the measurements. Each time - I entered the measured value for the RR (telling VCDS that it was low) which it accepted and let me save. The system would make adjustments and I would exit out and re-measure. Every time - the result was the same. The RR kept measuring out 10-12mm lower on the tape. One thing that was strange: when I bled the system all the way down to the ground, the RR sat on the ground a little lower than the LR. All the BAR levels showed flat, and the floor is level. I inspected all RR suspension components which turned out fine. After each bleed down - I would air everything all the way up with VCDS, then drop back to normal and re-run calibration - same result: successful calibration, but RR still 10-12mm lower than LR. I went to the measuring blocks and the RR was showing to be 10-12mm lower than the LR on four different occasions so the car knew that the RR was low the whole time. I would think that the system would have leveled itself out, but it didn't. I calibrated one last time and then went for a drive to see if anything would change.

During the test drive - I heard the compressor kick on/off every 15 or 20 seconds. Each time for just a few seconds. This got me thinking about the RR level sensor - could it be bad? I was under the impression that they either work or they don't? I thought about the RR level sensor always reading low - maybe it kept asking for air which is why the compressor kept kicking on? But the car always knew the RR was low because the measuring blocks showed it each time, but it always accepted the value and saved during calibration? Why wasn't the system adjusting after the calibration? On two different calibrations: the first one - I told the car that the RR was low, then on the second - I told the car that the LR was high. Neither method seemed to level out the rear - just the same result of the RR always being lower than the LR. I unplugged each sensor at all four corners to inspect for water / pin damage and the insides were all clean and dry, so no water penetration. I even unbolted both rear sensor arms and worked them around a few times and re-attached, but still got the same result in the end.

So - new compressor, new valve block, no leaks, and successful calibration. Only thing left is the level sensor, (maybe acceleration sensor?), or strut relief valve? I guess the RR strut could be bad? Strut relief valves are cheap, but I hate to throw a $150 level sensor or $700 strut at it on a whim! What am I missing??

ltooz_a6_a8_q7

Someone here replaced the rear inlet valves to fix his rear suspension problem a few weeks ago, search for it.
The pump should not be on while driving. There must be a leak at or after the valve block.
Reset the suspension to factory settings since you messed with VCDS, let the "sophisticated system" do its work. Most of savvy VCDS users seem to have weird problems...coincidences?
https://www.audiworld.com/forums/sho...8#post25219028
Cheers,
Louis

dvs_dave

aebarto11

After about three calibrations - I set everything back to factory height settings and ran back through it again thinking the same thing. Unfortunately - I had the same results (RR too low). When I ran out of the house this morning (8 hours sitting since I drove it last night) the level seemed to have held, but when I got home about 4:00, I could definitely see the car slightly leaning to the right. I put a tape on it and the RF had dropped to the same height as the RR so the whole right side is sitting about 1/2" lower than the left. My first guess would be a slight leak somewhere, but I'm also wondering if maybe the RF had just compensated for the low RR? I'm not convinced a minor leak like this would be the culprit here. When my RF strut went bad and started leaking from the bag (RF would be on the ground in 3-4 hours sitting) the compressor never engaged as much as it did while driving like it did last night (constantly kicking on the entire time). This is why the bad level sensor kept popping in my head - kinda makes sense if the car knows the RR is low - it would keep trying to air it up. There may be a slight leak which can be found and remedied, but the real mystery is why I can't get the car level (or think it's level) during calibration. I'm beginning to think these might be separate issues...

aebarto11

Nope - standing outside with laptop on roof. (I can neither confirm or deny that I may have done that back in the day when I first got VCDS though....!)

dvs_dave

abcspecialist

Compressor should stay off most of the time during driving.
Sounds like that the sensor or shock is wrong.
Note that there exist 2 types of struts, normal suspension and sport suspension. Note sure if ther difference is only stiffness or also ride height.

dvs_dave

aTOMic

Specifically, the pump should only come on at speeds >~25 MPH, IIRC.

aebarto11

I've been itching to try this but wasn't sure if they were interchangeable. I was concerned that they would be specific to a corner - kinda like a TPS in a tire. Since they're interchangeable - I'm thinking about biting the bullet and just ordering a new one. If it doesn't fix the problem - I'll have a spare on the shelf.

The RR strut is factory - only the FR has been replaced with an Arnott. I