Thought I would give the latest update, slowly knocking down the issues
Regarding the knock, I checked all the suspension linkages out and whilst they were torqued up correctly on assembly, the upper control arm (left) pinch bolt just nipped up a little more when I re-torqued it maybe 1/4 - 1/2 a turn max. To be honest I wasn’t totally comfortable that the bolts that came with the Mearle control arms were up to spec, so I purchased replacements from Audi, fitted and torqued to spec and that seems to have resolved the clunk. I think the parts just settled and needed a re-torque or the bolts relaxed, as the clunks started maybe 800 miles after the initial rebuild. I am surprised by this as having done suspension work before I haven’t had this issue, but glad it is resolved.
On the front end dropping, after doing some reading and positing on Audiworld, it seems the correct procedure to check the struts is to put the car in Jack mode (it stops the car from adjusting the ride height when parked, and eliminates the solenoid valve from what I understand) then measuring the drop as an accurate measure of the struts leaking. So I did this and the front was dropping 20-25mm in 24hrs, more so on the RHS which was the older strut (LHS just replaced). So I disconnected the sway bar to ensure the front drop is independent of each side, re set the car and the RHS front was dropping over 30-40mm in 24hrs.
Purchased a remanufactured Arnott for the RHS front, fitted it and left the car in Jack mode for 10 days and the car dropped 2-5mm across all corners, bearing in mind my measuring wasn’t totally scientific (tape measure by eye from the floor) and that the temp dropped around 20 degrees over that time I felt that was fine and acceptable. So based on this I really don’t think I have a leaking strut issue anymore. So all seemed fixed……….
Onto the G291 code, this code relates to a sensor in the valve block, some posts seem to link this code to a weak compressor. I have checked the lines to the compressor, valve block and struts and there are no visible leaks with the bubble test. And based on the above I’m confident my struts are good. On the compressor side as noted in previous posts the previous owner supplied a replacement one that was fitted by Audi last year, and I noted that after fitting the new RHS strut when I restarted the car it pumped the system up quickly and the compressor doesn’t run very long at all, mostly the car seems to be able to pump itself up from the accumulator. Based on those data points I feel the compressor is ok.
BUT, my problem is that I am still getting the G291 code, despite clearing it repeatedly, I was to the point that the car seemed fine and I was going to ignore it, until………….
Last night after parking the car a few hrs later the front right had dropped again ARRRRRRGGHHH, opening the drivers door and you can hear the valve block cycling and the car pumps itself back up again from the accumulator, no compressor running. Checked again this morning and the front right has dropped and the G291 is pretty much showing every time I drive the car. So I’m to the point where I am pretty sure my valve block is failing of has a sticking valve as the drop is random, and when it does drop it is severe. With the new struts I’m confident they are good, I do think I had a strut issue as in Jack mode the car was dropping.
I have an Audi used part specialist close to me and they have a used block for $139 and the guarantee the parts are tested, I’m going to get that and see if I can resolve this G291 code first, then check whether this random dropping is resolved. Looking on the bright side by the time I have finished this car will have a fully rebuilt suspension system, thank god I’m not paying a garage for labor.
