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Old 09-16-2018, 08:10 AM   #1
Tflgen2
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APR Stage 2 TSI boost fluctuating

As the title says, I have a boost fluctuating problem where it feels like a leak that opens up and closes. Power pulses under hard load. I have a relatively new stage 2 South bend clutch that is definitely not slipping.

I was not sure and replaced the N75 valve with no change.

I just installed a boost gauge (newsouth mechanical) and was very surprised by the results.

In 2nd and 3rd gear boost will build up to 15psi and immediate fall to 10 and boost back up to 15. It oscillates like this basically until I'm above 4500 rpm.

Sounds like a boost leak right?

Then I did a pull in 4th. Boost builds strong and hard to 20psi and holds.... I'm now at a loss.

APR tune adapting wrong? No obvious other issues.

See video: https://youtu.be/6sqWX-SZbuc
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Old 09-16-2018, 01:09 PM   #2
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What about the DV?
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Old 09-16-2018, 01:26 PM   #3
Tflgen2
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Replaced with rev D probably 30k ago
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Old 09-16-2018, 02:24 PM   #4
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If you have Vcds scan and run logs, also switch back to stock mode and see if it improves or not and Scan and also run logs.
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Old 09-16-2018, 06:22 PM   #5
Tflgen2
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Do have vcds, just had desired boost not met code come up.
Won't be able to log tonight. Will try switching back to stock to see what happens.

With more testing it also happens in 4th gear when starting from higher rpms. (Harder to test b/c moving speed).
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Old 09-17-2018, 11:46 AM   #6
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So it doesn't appear to happen with stock although there is some slight hiccup when getting up to full (read 9psi) boost.

With VCDS, what should I focus on? Since my adapter doesn't support turbo mode, what are the minimum points to log? I'm not really able to do a full 4th gear pull, but I can capture the problem area.
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Old 09-17-2018, 11:56 AM   #7
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The boost target is lower in stock mode so the turbo can compensate by spinning faster but you probably have a leak. Check all pipes connections and do a smoke test.
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Old 09-17-2018, 01:17 PM   #8
Tflgen2
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Ok, will see what I can do. If it does have a boost leak, can you explain how it can hold 20psi in the video though?
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Old 09-17-2018, 01:21 PM   #9
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I'd check that DV again. With it sometimes holding 20psi makes me feel like that's your issue.
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Old 09-17-2018, 02:25 PM   #10
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Quote:
Originally Posted by Tflgen2 View Post
can you explain how it can hold 20psi in the video though?
That's also why I would have said the DV but a reason I see (not sure if it's actually a valid theory) can be that there is more exhaust flow in 4th (more engine load, hotter gases) so that the turbo spins fast enough to reach and hold that "spot", if you look closely you will also see that there is some hesitation until it reaches it. A way to test that theory would be to go full throttle uphill in 3rd and see if it reaches 20 psi.

Last edited by vwengineer; 09-17-2018 at 02:46 PM.
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Old 09-17-2018, 05:23 PM   #11
Tflgen2
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Quote:
Originally Posted by vwengineer View Post
That's also why I would have said the DV but a reason I see (not sure if it's actually a valid theory) can be that there is more exhaust flow in 4th (more engine load, hotter gases) so that the turbo spins fast enough to reach and hold that "spot", if you look closely you will also see that there is some hesitation until it reaches it. A way to test that theory would be to go full throttle uphill in 3rd and see if it reaches 20 psi.

Did the low rpm high load 3rd gear test and as predicted, 20psi. What does this mean? Bad DV?
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Old 09-17-2018, 05:41 PM   #12
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Just that you probably have a small leak that prevent the building of boost. The best would be to do a smoke test and if you cannot find a leak then it's probably the DV.

Usually if the DV cannot hold the boost, it will open/close continuously which makes a bit what you see, however it seems stable at 20psi so I don't think it's that but it can leak, check if there is oil in the connector.
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Old Yesterday, 09:46 AM   #13
5aprilc
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I was reading something about the Revision D sometimes failing, and that some people have had luck with Revision G.
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Old Yesterday, 10:38 AM   #14
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I also read that the revision D is more robust but leaks some boost by design while revision G seals better but is less durable. I also think revision D is more intended for K04 cars because while they are interchangeables VW still makes both and ETKA gives revision G as the latest reference (for my car at least) while the revision D is the latest given for the Audi S3. That said a lot of people are using revision D without issues and both are compatible with the Golf GTI.

https://www.audi-sport.net/xf/thread...-valve.184392/

Last edited by vwengineer; Yesterday at 11:41 AM.
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Old Yesterday, 11:14 AM   #15
5aprilc
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I've put about 20K miles on my Revision D Diverter Valve, so far so good, but I also don't have my boost gauge hooked up so I could be leaking some boost pressure and not even know it.
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