1st Gear Power Cut

[Jim Haseltine]

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.

[cammmy]

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

[cammmy]

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?

[Pajo]

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.

[cammmy]

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.

[IanH755]

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

[cammmy]

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.

[IanH755]

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.

[cammmy]

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

[cammmy]

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