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Boost fluctuations and hesitation: APR Stage 1

thatspsychotic

thatspsychotic

Ready to race!
I've been experiencing this gradually getting worse since flashing APR Stage 1 V2.1:



Boost fluctuations around the boost threshold along with hesitation at the same time. Consistently does this (or sounds more like compressor surge when its warmer out) in this situation.

Anyone else seen this? Maybe N75 valve problem? Tune too aggressive with using DV to control boost?
 
F

FriggenT1

Banned
I don't really think one can hear compressor surge, I think that's the most commonly confused issue with WG flutter, etc.
 
thatspsychotic

thatspsychotic

Ready to race!
FriggenT said:
I don't really think one can hear compressor surge, I think that's the most commonly confused issue with WG flutter, etc.
Click to expand...

One can definitely hear compressor surge, and I'm not sure that one can actually hear "WG flutter"




However, my video and issue I'm not suggesting that it is compressor surge, but some kind of boost control issue, like bad N75 valve, etc.
 
F

FriggenT1

Banned
Hmmm, have you done a boost leak test? Like it's trying to build and it hits that point where it starts to leak, but maybe it just seals itself. Checked the TOP connection? It bounces so fast that it looks more like a possible software issue imo.
 
F

FriggenT1

Banned
Ohhh wait, you said DV, I just saw the DV+ that doesn't always do well with some software. I'd take it off and try that first.
 
thatspsychotic

thatspsychotic

Ready to race!
FriggenT said:
Ohhh wait, you said DV, I just saw the DV+ that doesn't always do well with some software. I'd take it off and try that first.
Click to expand...

Yeah that was one of my fears, the extra mass of the DV+ causing it to vent too much boost. Still seems like a backwards way of controlling boost rather than N75. Will have to pick up a rev D DV to test.
 
thatspsychotic

thatspsychotic

Ready to race!
snobrdrdan said:
I have one laying around...used it for a quick test & then took it off.
Click to expand...

What were you testing? Whether your rev G was leaking boost?

FriggenT said:
Just put your old one back together?
Click to expand...

I have rev G, I'm fairly sure it was leaking boost even with the V1.2 tune ages ago, thats why I went DV+ in the first place.

I would like to test rev D, but I'm not convinced that its the DV at all. The boost fluctuation is almost sinusoidal and is only a few PSI in magnitude, as if the car is hunting for the correct boost level. That is what made me think of the N75 valve first. If it is the N75, that could also make the ECU lean on the DV more to control overshoot, barely cracking the DV to modulate the pressure. Even that doesn't make a whole lot of sense, because the boost is fluctuating before it even gets to the peak boost level once things settle at >3500 RPM

I have autocross tomorrow so I can't test anything out, but I also want to rule out the low hanging fruit like cleaning the MAF, even changing out my air filter, etc. to make sure it's not something caused by wonky MAF readings. This isn't a problem in autocross because most of the time is spent over 3500 RPM in 2nd gear anyways, and the car has too much power to put to the ground well with my worn tires and stock suspension.
 
snobrdrdan

snobrdrdan

former GTI owner
thatspsychotic said:
What were you testing? Whether your rev G was leaking boost?
Click to expand...

Yeah. It ended up being the tune though after I logged it and found out it wasn't leaking boost at all. It just wasn't meeting the requested PSI it was supposed to and needed some tweaking in the software
 
damagi123

damagi123

Go Kart Champion
im having the same problem WOT on 3rd or 4th from 2500 - 3500 RPM
im on stg2 2.3b and it wasnt happening at first only after a couple weeks.

im also going to test boost leak and n75 but also what about pcv?
 
thatspsychotic

thatspsychotic

Ready to race!
damagi123 said:
im having the same problem WOT on 3rd or 4th from 2500 - 3500 RPM
im on stg2 2.3b and it wasnt happening at first only after a couple weeks.

im also going to test boost leak and n75 but also what about pcv?
Click to expand...

I replaced my PCV plate after going V2.1, and it didn't really seem to help the issue.

I've found that in really hot weather I get much more of a compressor surge sound, but in cooler weather it is much more boost fluctuation.

To me, this has to be either N75, or the tune. I really don't trust how the APR tune adapts. It seems to be it feels great when first flashed, but it develops maladaptations over time. It seems like it almost gets tired of using the N75 for boost control and starts using the DV and throttle plate instead. Pretty strange strategy.

Any non-APR folks have issues similar to this?
 
Blaznjoe

Blaznjoe

Drag Race Newbie
thatspsychotic said:
I replaced my PCV plate after going V2.1, and it didn't really seem to help the issue.

I've found that in really hot weather I get much more of a compressor surge sound, but in cooler weather it is much more boost fluctuation.

To me, this has to be either N75, or the tune. I really don't trust how the APR tune adapts. It seems to be it feels great when first flashed, but it develops maladaptations over time. It seems like it almost gets tired of using the N75 for boost control and starts using the DV and throttle plate instead. Pretty strange strategy.

Any non-APR folks have issues similar to this?
Click to expand...

I'm GIAC Stage 2 tuned and started getting Boost fluctuations after a hard track day (road course) this past August. I chased for boost leaks and found nothing. Bought a new OEM n75 valve and replaced it two days ago with no other changes. Problem solved for me. No more fluctuations or hesitations. :thumbup:
I will say that replacing this little valve was a royal PITA :mad0259: Very little space around it. I highly recommend very long needle nose pliers. Maybe even long angled needle nose pliers. Also, upgrading to the USP turbo delete could make the job easier as well. (I kinda wish I did this.) I had to remove my turbo muffler in order to get my hands in there.

Other statistics:
53k miles
Chipped/Tuned for 40k+
Pump (91oct) and Race file did not change hesitation issue
Still on original PCV
ECS CatchCan for about 10k miles
old n75 had oil in it. (Similar to DV)
no check engine light or error codes (I have VAG-COM)
 
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