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I wouldn't put anything electronic in an ultrasound cleaner. We never risked anything other than a quick spray with carb cleaner followed by a shake to get rid of any excess liquid then allowing them to air dry.

Righto, my plan was to dangle them so just the sensor part was in the liquid but I'll try spraying first.

Unfortunately, no joy. Haven't put the laptop on it but it has the same symptoms. Any other potential causes? Do I need to replace the sensors next?

I'm imagining it's not likely to be a mechanical issue, as it only happens in 1st?

Did you ever make a Boost/Fuel Pressure graph with the VCDS? It can record it im sure. Other than that, do you know if your DV's function properly? I imagine a high boost spike in 1st gear compared to all the others, so perhaps thats why it only cuts in 1st.

No, I'll look that up and see what it's doing. Thanks.

Are the DV valves just a spring or do they get a reference from after the throttle too? Regardless, If they are opening under throttle, I'd consider that a failure of the boost control system that needs fixing.

The DV's use a Spring being opened by vacuum pressure which is controlled by the N249 solenoid and this can get "sticky" with age - Here's a post I made a few year ago with part numbers etc - viewtopic.php?t=135004#p938611 - and it's £200+ to replace IIRC.

Item 32 - https://audi.7zap.com/en/rdw/audi+rs6+r ... 145010/#32

Which is shown here connected to the 2 DV's as Item 26 - https://audi.7zap.com/en/rdw/audi+rs6+r ... 133030/#26

Thanks Ian, what's the likelyhood that's causing the issue? I would have thought the DVs are only supposed to open when the throttle snaps shut, rather than being a method of boost control under load?

I need to get out in it this week and see what boost it's recording.

Yeap, if everything is working correctly the N249 should only open the DV's when the throttle is shut.

Maybe, and this is a pure guess, if your N249 was acting up under the "G-force" of initial acceleration (maybe a pipe being pulled etc), it'd open both DV's to dump all the boost from the intake causing a power cut - It's a lot of money to replace a sensor on a pure guess like that so I'd be tempted to keep looking for pipe splits etc before I looking for a cheap Sensor from a scrap dealer/ebay etc to try out, or maybe even a fellow nearby RS246'er could lend you theirs (it's a 10min swap)?

A boost log (demand vs actual) would be a great help, alongside a log of Fuel rail pressures too incase it's fuel related.

Cool, thanks. The only two codes were the overboost on both sensors in the charge pipes. It's definitely not a boost leak, you can hear the ignition cutting.

I'll try get it out for a logging session tomorrow.

Ta

Okay, did two runs, both triggered boost cut in first. Log attached. Anyone able to make any sense of it?

Forum won't allow CSV attachments so it's .txt

Ta
Cam

It looks like it boost cut twice in the first half of the log and, to my old eyes, it looks like both boost cuts are when the Actual Boost hits just over 2bar vs a Demanded Boost of 1.9Bar with both happening first at about 4350rpm-ish and then again at about 5650rpm-ish (I made the lines red in the image below), which are shown on lines 21 and 23 on the image below (ignore line 25, I think it's the boost spike on gear change as the DV's open looking at Demand vs Actual) so I wonder if 2Bar is a set hard limit somewhere and might be the cause?

If it is the issue, then it's the sort of thing that only a map change would actually fix by bringing the Demanded Boost down to 1.85Bar to allow the Actual Boost spike to only reach 1.95Bar.

For those who also want to understand the Excel file image (its at 4k resolution so click on it for the big version), as best as I can describe it -

Group 1 shows the Engine RPM.
Group 2 shows the Boost Pressure inside the intake manifold as detected by the G71 sensor.
Group 3 is a repeat of Group 2.
Group 115 shows both the Demanded (or "specified") Boost from ECU which is controlled by the N75/N274 sensors on each turbo and it also shows the Actual Boost as well.
Group 117 shows a repeat of the Demanded Boost.
Group 118 & 119 shows the Actual Boost from before the Throttle Bodies detected by the G31 and G447 sensors.

Thanks for the analysis. I figured some might be duplicates but I just ticked everything related to boost.

Any idea why this would have only started a couple years after getting the car and only in first? It also seems both sides are overboosting? Difficult to imagine both N75 valves going wonky simultaneously? Do the values for the N75s make sense? Lastly, i'm guessing pressure values are absolute i.e. 2 bar means 1 bar boost?

The difference between demanded vs actual pressure at the boost-cut is extremely small, like 1.5psi difference and wouldn't normally be an issue in anyway, I think its the sensor reading hitting 2bar which seems to activate a safety boost cut, although I did notice that your fuel rail pressure also drops 30psi (140 down to 110psi) at the same time (4300rpm) so I'm guessing your ECU might be reducing fuel pressure (maybe as part of pulling timing?) as well as boost as part of the safety stuff.

However, it's all just guesswork from myself without knowing more about how the ECU deals with issues.

Absolute - Yeap, these are absolute pressures so 2bar reading = 1bar atmosphere + 1bar boost etc.

Cool, thanks for that. I'll have to mull it over.

Been busy but came back to this. Did what I try not to do and just threw some parts at it. Changed all 3 map sensors with OE/OEM Bosch units bit still have the issue. It's only in 1st. Above that seems fine.

Are there any boost related adaptations I can run or reset in VCDS?